diff --git a/CMakeLists.txt b/CMakeLists.txt
index 753cda2f..103d4b7a 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -11,6 +11,8 @@ if (POLICY CMP0135)
     cmake_policy(SET CMP0135 NEW)
 endif ()
 
+set(CMAKE_POLICY_DEFAULT_CMP0077 NEW)
+
 project(dxFeedGraalCxxApi)
 
 set(DXFCXX_VERSION "0.1.3" CACHE STRING "The dxFeed Graal CXX API package version")
@@ -89,6 +91,9 @@ FetchContent_MakeAvailable(DxFeedGraalNativeSdk)
 add_subdirectory(third_party/utfcpp-3.2.3)
 set(FMT_INSTALL OFF)
 add_subdirectory(third_party/fmt-10.0.0)
+set(BUILD_TZ_LIB ON)
+set(USE_SYSTEM_TZ_DB ON)
+add_subdirectory(third_party/date-3.0.1)
 
 # find_package(utf8cpp)
 # find_package(fmt)
@@ -300,8 +305,8 @@ if (DXFCXX_USE_PRECOMPILED_HEADERS)
     target_precompile_headers(${PROJECT_NAME}_static PRIVATE include/dxfeed_graal_cpp_api/internal/PrecompiledHeaders.hpp)
 endif ()
 
-target_link_libraries(${PROJECT_NAME}_static PUBLIC DxFeedGraalNativeSdk utf8cpp fmt::fmt-header-only)
-target_link_libraries(${PROJECT_NAME} PUBLIC DxFeedGraalNativeSdk utf8cpp fmt::fmt-header-only)
+target_link_libraries(${PROJECT_NAME}_static PUBLIC DxFeedGraalNativeSdk utf8cpp fmt::fmt-header-only date::date)
+target_link_libraries(${PROJECT_NAME} PUBLIC DxFeedGraalNativeSdk utf8cpp fmt::fmt-header-only date::date)
 
 if (DXFCXX_ENABLE_ASAN_UBSAN)
     target_compile_options(${PROJECT_NAME} PRIVATE "-fsanitize=address" "-fsanitize=undefined")
diff --git a/DEPENDENCIES.md b/DEPENDENCIES.md
index 47e614b1..0bcad066 100644
--- a/DEPENDENCIES.md
+++ b/DEPENDENCIES.md
@@ -6,7 +6,8 @@
 - [utfcpp](https://github.com/nemtrif/utfcpp) v3.2.3
 - [fmt](https://github.com/fmtlib/fmt) v10.0.0
 - [doctest](https://github.com/doctest/doctest) v2.4.11 (Tests)
-- [range-v3](https://github.com/ericniebler/range-v3) v0.12 (Code & Samples)
+- [range-v3](https://github.com/ericniebler/range-v3) v0.12
+- [date] (https://github.com/HowardHinnant/date) v3.0.1
 
 ## Run-time
 
diff --git a/THIRD_PARTY_LICENSES.md b/THIRD_PARTY_LICENSES.md
index 9feb3988..8103b81d 100644
--- a/THIRD_PARTY_LICENSES.md
+++ b/THIRD_PARTY_LICENSES.md
@@ -7,4 +7,7 @@
 3. doctest - https://github.com/doctest/doctest/blob/master/LICENSE.txt  
    SPDX-License-Identifier: MIT
 4. range-v3 - https://github.com/ericniebler/range-v3/blob/master/LICENSE.txt
-   SPDX-License-Identifier: BSL-1.0
\ No newline at end of file
+   SPDX-License-Identifier: BSL-1.0
+5. date - https://github.com/HowardHinnant/date/blob/master/LICENSE.txt
+   SPDX-License-Identifier: MIT
+   
\ No newline at end of file
diff --git a/samples/cpp/DxFeedConnect/CMakeLists.txt b/samples/cpp/DxFeedConnect/CMakeLists.txt
index 69c7a0ef..d35b042a 100644
--- a/samples/cpp/DxFeedConnect/CMakeLists.txt
+++ b/samples/cpp/DxFeedConnect/CMakeLists.txt
@@ -49,7 +49,7 @@ if (DXFCXX_ENABLE_VS_ASAN)
 endif ()
 
 if (DXFCXX_ENABLE_ASAN_UBSAN)
-    target_link_libraries(${PROJECT_NAME} PRIVATE dxfcxx)
+    target_link_libraries(${PROJECT_NAME} PRIVATE dxfcxx date::date date::date-tz)
     target_compile_definitions(${PROJECT_NAME} PRIVATE DXFCPP_USE_DLLS)
     add_custom_command(TARGET ${PROJECT_NAME} POST_BUILD COMMAND ${CMAKE_COMMAND} -E copy_if_different
             $<TARGET_FILE:dxfcxx::graal>
@@ -59,7 +59,7 @@ if (DXFCXX_ENABLE_ASAN_UBSAN)
     target_compile_options(${PROJECT_NAME} PRIVATE "-fsanitize=address" "-fsanitize=undefined")
     target_link_options(${PROJECT_NAME} PRIVATE "-fsanitize=address" "-fsanitize=undefined")
 else ()
-    target_link_libraries(${PROJECT_NAME} PRIVATE dxfcxx)
+    target_link_libraries(${PROJECT_NAME} PRIVATE dxfcxx date::date date::date-tz)
     target_compile_definitions(${PROJECT_NAME} PRIVATE DXFCPP_USE_DLLS)
     add_custom_command(TARGET ${PROJECT_NAME} POST_BUILD COMMAND ${CMAKE_COMMAND} -E copy_if_different
             $<TARGET_FILE:dxfcxx::graal>
diff --git a/samples/cpp/DxFeedConnect/src/main.cpp b/samples/cpp/DxFeedConnect/src/main.cpp
index 2d1530f9..149905b3 100644
--- a/samples/cpp/DxFeedConnect/src/main.cpp
+++ b/samples/cpp/DxFeedConnect/src/main.cpp
@@ -5,7 +5,8 @@
 
 #include <atomic>
 #include <mutex>
-#include <chrono>
+#include <date/date.h>
+#include <date/tz.h>
 
 using namespace dxfcpp;
 using namespace dxfcpp::literals;
@@ -43,9 +44,7 @@ DxFeedConnect <address> <types> <symbols> [<time>]
 }
 
 int main(int argc, char *argv[]) {
-    const std::chrono::zoned_time cur_time{ std::chrono::current_zone(),
-                                           std::chrono::system_clock::now() };
-    std::cout << cur_time << '\n';
+    //std::cout << date::current_zone()->name() << std::endl;
 
     return 0;
 
diff --git a/third_party/date-3.0.1/.gitignore b/third_party/date-3.0.1/.gitignore
new file mode 100644
index 00000000..e88e3be3
--- /dev/null
+++ b/third_party/date-3.0.1/.gitignore
@@ -0,0 +1,194 @@
+#ignore thumbnails created by windows
+Thumbs.db
+#Ignore files build by Visual Studio
+*.obj
+*.exe
+*.pdb
+*.user
+*.aps
+*.pch
+*.vspscc
+*_i.c
+*_p.c
+*.ncb
+*.suo
+*.tlb
+*.tlh
+*.bak
+*.cache
+*.ilk
+*.log
+[Bb]in
+[Dd]ebug*/
+*.lib
+*.sbr
+obj/
+[Rr]elease*/
+_ReSharper*/
+[Tt]est[Rr]esult*
+.idea/
+*.opensdf
+## Ignore Visual Studio temporary files, build results, and
+## files generated by popular Visual Studio add-ons.
+# User-specific files
+*.suo
+*.user
+*.userosscache
+*.sln.docstates
+# User-specific folders
+*.sln.ide/
+# Build results
+[Dd]ebug/
+[Dd]ebugPublic/
+[Rr]elease/
+[Rr]eleases/
+x64/
+x86/
+build/
+bld/
+[Bb]in/
+[Oo]bj/
+# Roslyn cache directories
+*.ide/
+# MSTest test Results
+[Tt]est[Rr]esult*/
+[Bb]uild[Ll]og.*
+#NUNIT
+*.VisualState.xml
+TestResult.xml
+# Build Results of an ATL Project
+[Dd]ebugPS/
+[Rr]eleasePS/
+dlldata.c
+*_i.c
+*_p.c
+*_i.h
+*.ilk
+*.meta
+*.obj
+*.pch
+*.pdb
+*.pgc
+*.pgd
+*.rsp
+*.sbr
+*.tlb
+*.tli
+*.tlh
+*.tmp
+*.tmp_proj
+*.log
+*.vspscc
+*.vssscc
+.builds
+*.pidb
+*.svclog
+*.scc
+# Chutzpah Test files
+_Chutzpah*
+# Visual C++ cache files
+ipch/
+*.aps
+*.ncb
+*.opensdf
+*.sdf
+*.cachefile
+# Visual Studio profiler
+*.psess
+*.vsp
+*.vspx
+# TFS 2012 Local Workspace
+$tf/
+# Guidance Automation Toolkit
+*.gpState
+# ReSharper is a .NET coding add-in
+_ReSharper*/
+*.[Rr]e[Ss]harper
+*.DotSettings.user
+# JustCode is a .NET coding addin-in
+.JustCode
+# TeamCity is a build add-in
+_TeamCity*
+# DotCover is a Code Coverage Tool
+*.dotCover
+# NCrunch
+_NCrunch_*
+.*crunch*.local.xml
+# MightyMoose
+*.mm.*
+AutoTest.Net/
+# Web workbench (sass)
+.sass-cache/
+# Installshield output folder
+[Ee]xpress/
+# DocProject is a documentation generator add-in
+DocProject/buildhelp/
+DocProject/Help/*.HxT
+DocProject/Help/*.HxC
+DocProject/Help/*.hhc
+DocProject/Help/*.hhk
+DocProject/Help/*.hhp
+DocProject/Help/Html2
+DocProject/Help/html
+# Click-Once directory
+publish/
+# Publish Web Output
+*.[Pp]ublish.xml
+*.azurePubxml
+# TODO: Comment the next line if you want to checkin your web deploy settings 
+# but database connection strings (with potential passwords) will be unencrypted
+*.pubxml
+*.publishproj
+# NuGet Packages
+*.nupkg
+# The packages folder can be ignored because of Package Restore
+**/packages/*
+# except build/, which is used as an MSBuild target.
+!**/packages/build/
+# If using the old MSBuild-Integrated Package Restore, uncomment this:
+#!**/packages/repositories.config
+# Windows Azure Build Output
+csx/
+*.build.csdef
+# Windows Store app package directory
+AppPackages/
+# Others
+sql/
+*.Cache
+ClientBin/
+[Ss]tyle[Cc]op.*
+~$*
+*~
+*.dbmdl
+*.dbproj.schemaview
+*.pfx
+*.publishsettings
+node_modules/
+bower_components/
+# RIA/Silverlight projects
+Generated_Code/
+# Backup & report files from converting an old project file
+# to a newer Visual Studio version. Backup files are not needed,
+# because we have git ;-)
+_UpgradeReport_Files/
+Backup*/
+UpgradeLog*.XML
+UpgradeLog*.htm
+# SQL Server files
+*.mdf
+*.ldf
+# Business Intelligence projects
+*.rdl.data
+*.bim.layout
+*.bim_*.settings
+# Microsoft Fakes
+FakesAssemblies/
+*.suo
+*.vcxproj.filters
+*.npp
+CMakeFiles/*
+nbproject/*
+*.cd
+*.cd
+a.out
+cmake-build-debug/*
diff --git a/third_party/date-3.0.1/.travis.yml b/third_party/date-3.0.1/.travis.yml
new file mode 100644
index 00000000..ca8991a8
--- /dev/null
+++ b/third_party/date-3.0.1/.travis.yml
@@ -0,0 +1,147 @@
+language: cpp
+
+env:
+  global:
+    - CMAKE_EXTRA_CONF="-DCOMPILE_WITH_C_LOCALE=ON"
+    - CTEST_OUTPUT_ON_FAILURE=1
+
+matrix:
+  include:
+
+    - name: "Ubuntu 16.04 LTS (Xenial Xerus) GCC 7"
+      os: linux
+      dist: xenial
+      addons:
+        apt:
+          sources:
+            - ubuntu-toolchain-r-test
+          packages:
+            - g++-7
+      env:
+        - MATRIX_EVAL="CC=gcc-7 && CXX=g++-7"
+
+    - name: "Ubuntu 16.04 LTS (Xenial Xerus) GCC 8"
+      os: linux
+      dist: xenial
+      addons:
+        apt:
+          sources:
+            - ubuntu-toolchain-r-test
+          packages:
+            - g++-8
+      env:
+        - MATRIX_EVAL="CC=gcc-8 && CXX=g++-8"
+
+    - name: "Ubuntu 16.04 LTS (Xenial Xerus) GCC 9"
+      os: linux
+      dist: xenial
+      addons:
+        apt:
+          sources:
+            - ubuntu-toolchain-r-test
+          packages:
+            - g++-9
+      env:
+        - MATRIX_EVAL="CC=gcc-9 && CXX=g++-9"
+
+    - name: "Ubuntu 18.04 LTS (Bionic Beaver) GCC 7"
+      os: linux
+      dist: bionic
+      addons:
+        apt:
+          sources:
+            - ubuntu-toolchain-r-test
+          packages:
+            - g++-7
+      env:
+        - MATRIX_EVAL="CC=gcc-7 && CXX=g++-7"
+
+    - name: "Ubuntu 18.04 LTS (Bionic Beaver) GCC 8"
+      os: linux
+      dist: bionic
+      addons:
+        apt:
+          sources:
+            - ubuntu-toolchain-r-test
+          packages:
+            - g++-8
+      env:
+        - MATRIX_EVAL="CC=gcc-8 && CXX=g++-8"
+
+    - name: "Ubuntu 18.04 LTS (Bionic Beaver) Clang 6"
+      os: linux
+      dist: bionic
+      addons:
+        apt:
+          sources:
+            - llvm-toolchain-bionic-6.0
+          packages:
+            - clang-6.0
+      env:
+        - MATRIX_EVAL="CC=clang-6.0 && CXX=clang++-6.0"
+
+    - name: "Ubuntu 18.04 LTS (Bionic Beaver) Clang 7"
+      os: linux
+      dist: bionic
+      addons:
+        apt:
+          sources:
+            - llvm-toolchain-bionic-7
+          packages:
+            - clang-7
+      env:
+        - MATRIX_EVAL="CC=clang-7 && CXX=clang++-7"
+
+    - name: "Ubuntu 18.04 LTS (Bionic Beaver) Clang 8"
+      os: linux
+      dist: bionic
+      addons:
+        apt:
+          sources:
+            - llvm-toolchain-bionic-8
+          packages:
+            - clang-8
+      env:
+        - MATRIX_EVAL="CC=clang-8 && CXX=clang++-8"
+
+    - &macos
+      name: xcode10
+      os: osx
+      osx_image: xcode10.2
+      env:
+        - CMAKE_EXTRA_CONF=""
+      addons:
+        homebrew:
+          packages:
+            - bash
+            - ninja
+
+    - <<: *macos
+      name: xcode9
+      # xcode 9 only works if we tell it to use c++14 explicitly
+      env:
+        - CMAKE_EXTRA_CONF="-DCMAKE_CXX_STANDARD=14"
+      osx_image: xcode9.4
+
+    - <<: *macos
+      osx_image: xcode11
+      name: xcode11
+
+before_install:
+  - eval "${MATRIX_EVAL}"
+  - ci/install_cmake.sh 3.15.2
+  - export OPENSSL_ROOT=$(brew --prefix openssl@1.1)
+  - if [ "$(uname)" = "Darwin" ] ; then export PATH="$HOME/cmake/CMake.app/Contents/bin:${PATH}"; fi
+  - if [ "$(uname)" = "Linux" ] ; then export PATH="$HOME/cmake/bin:${PATH}"; fi
+
+cache:
+  directories:
+    - $HOME/cmake
+
+script:
+  - mkdir -p build
+  - cd build
+  - eval cmake -DENABLE_DATE_TESTING=ON -DBUILD_SHARED_LIBS=ON ${CMAKE_EXTRA_CONF} ..
+  - cmake --build . --parallel
+  - cmake --build . --parallel --target testit
+
diff --git a/third_party/date-3.0.1/CMakeLists.txt b/third_party/date-3.0.1/CMakeLists.txt
new file mode 100644
index 00000000..012512ae
--- /dev/null
+++ b/third_party/date-3.0.1/CMakeLists.txt
@@ -0,0 +1,277 @@
+#[===================================================================[
+   date library by Howard Hinnant
+
+   CMake projects that wish to use this library should consider
+   something like the following :
+
+     include( FetchContent )
+     FetchContent_Declare( date_src
+       GIT_REPOSITORY https://github.com/HowardHinnant/date.git
+       GIT_TAG        v3.0.0  # adjust tag/branch/commit as needed
+     )
+     FetchContent_MakeAvailable(date_src)
+     ...
+     target_link_libraries (my_target PRIVATE date::date)
+
+#]===================================================================]
+
+cmake_minimum_required( VERSION 3.7 )
+
+project( date VERSION 3.0.0 )
+set(ABI_VERSION 3) # used as SOVERSION, increment when ABI changes
+
+include( GNUInstallDirs )
+
+get_directory_property( has_parent PARENT_DIRECTORY )
+
+# Override by setting on CMake command line.
+set( CMAKE_CXX_STANDARD 17 CACHE STRING "The C++ standard whose features are requested." )
+
+option( USE_SYSTEM_TZ_DB "Use the operating system's timezone database" OFF )
+option( MANUAL_TZ_DB "User will set TZ DB manually by invoking set_install in their code" OFF )
+option( USE_TZ_DB_IN_DOT "Save the timezone database in the current folder" OFF )
+option( BUILD_SHARED_LIBS  "Build a shared version of library" OFF )
+option( ENABLE_DATE_TESTING "Enable unit tests" OFF )
+option( DISABLE_STRING_VIEW "Disable string view" OFF )
+option( COMPILE_WITH_C_LOCALE "define ONLY_C_LOCALE=1" OFF )
+option( BUILD_TZ_LIB "build/install of TZ library" OFF )
+
+if( ENABLE_DATE_TESTING AND NOT BUILD_TZ_LIB )
+    message(WARNING "Testing requested, bug BUILD_TZ_LIB not ON - forcing the latter")
+    set (BUILD_TZ_LIB ON CACHE BOOL "required for testing" FORCE)
+endif( )
+
+function( print_option OPT )
+    if ( NOT DEFINED PRINT_OPTION_CURR_${OPT} OR ( NOT PRINT_OPTION_CURR_${OPT} STREQUAL ${OPT} ) )
+        set( PRINT_OPTION_CURR_${OPT} ${${OPT}} CACHE BOOL "" )
+        mark_as_advanced(PRINT_OPTION_CURR_${OPT})
+        message( "# date: ${OPT} ${${OPT}}" )
+    endif( )
+endfunction( )
+
+print_option( USE_SYSTEM_TZ_DB )
+print_option( MANUAL_TZ_DB )
+print_option( USE_TZ_DB_IN_DOT )
+print_option( BUILD_SHARED_LIBS  )
+print_option( ENABLE_DATE_TESTING )
+print_option( DISABLE_STRING_VIEW )
+
+#[===================================================================[
+   date (header only) library
+#]===================================================================]
+add_library( date INTERFACE )
+add_library( date::date ALIAS date )
+target_include_directories( date INTERFACE
+    $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
+    $<INSTALL_INTERFACE:include> )
+# adding header sources just helps IDEs
+target_sources( date INTERFACE
+    $<BUILD_INTERFACE:${CMAKE_CURRENT_LIST_DIR}/include>$<INSTALL_INTERFACE:include>/date/date.h
+    # the rest of these are not currently part of the public interface of the library:
+    $<BUILD_INTERFACE:${CMAKE_CURRENT_LIST_DIR}/include/date/solar_hijri.h>
+    $<BUILD_INTERFACE:${CMAKE_CURRENT_LIST_DIR}/include/date/islamic.h>
+    $<BUILD_INTERFACE:${CMAKE_CURRENT_LIST_DIR}/include/date/iso_week.h>
+    $<BUILD_INTERFACE:${CMAKE_CURRENT_LIST_DIR}/include/date/julian.h>
+)
+if (CMAKE_VERSION VERSION_GREATER_EQUAL 3.15)
+    # public headers will get installed:
+    set_target_properties( date PROPERTIES PUBLIC_HEADER include/date/date.h )
+endif ()
+
+# These used to be set with generator expressions,
+#
+#   ONLY_C_LOCALE=$<IF:$<BOOL:${COMPILE_WITH_C_LOCALE}>,1,0>
+#
+# which expand in the output target file to, e.g.
+#
+#   ONLY_C_LOCALE=$<IF:$<BOOL:FALSE>,1,0>
+#
+# This string is then (somtimes?) not correctly interpreted.
+if ( COMPILE_WITH_C_LOCALE )
+  # To workaround libstdc++ issue https://github.com/HowardHinnant/date/issues/388
+  target_compile_definitions( date INTERFACE ONLY_C_LOCALE=1 )
+else()
+  target_compile_definitions( date INTERFACE ONLY_C_LOCALE=0 )
+endif()
+if ( DISABLE_STRING_VIEW )
+  target_compile_definitions( date INTERFACE HAS_STRING_VIEW=0 -DHAS_DEDUCTION_GUIDES=0 )
+endif()
+
+#[===================================================================[
+   tz (compiled) library
+#]===================================================================]
+if( BUILD_TZ_LIB )
+    add_library( date-tz )
+    target_sources( date-tz
+      PUBLIC
+        $<BUILD_INTERFACE:${CMAKE_CURRENT_LIST_DIR}/include>$<INSTALL_INTERFACE:include>/date/tz.h
+      PRIVATE
+        include/date/tz_private.h
+        src/tz.cpp )
+    if ( IOS )
+      target_sources( date-tz
+        PUBLIC
+          $<BUILD_INTERFACE:${CMAKE_CURRENT_LIST_DIR}/include>$<INSTALL_INTERFACE:include>/date/ios.h
+        PRIVATE
+          src/ios.mm )
+    endif()
+    add_library( date::date-tz ALIAS date-tz )
+    target_link_libraries( date-tz PUBLIC date )
+    target_include_directories( date-tz PUBLIC
+        $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
+        $<INSTALL_INTERFACE:include> )
+
+    if ( USE_SYSTEM_TZ_DB OR MANUAL_TZ_DB )
+      target_compile_definitions( date-tz PRIVATE AUTO_DOWNLOAD=0 HAS_REMOTE_API=0 )
+    else()
+      target_compile_definitions( date-tz PRIVATE AUTO_DOWNLOAD=1 HAS_REMOTE_API=1 )
+    endif()
+
+    if ( USE_SYSTEM_TZ_DB AND NOT WIN32 AND NOT MANUAL_TZ_DB )
+      target_compile_definitions( date-tz PRIVATE INSTALL=. PUBLIC USE_OS_TZDB=1 )
+    else()
+      target_compile_definitions( date-tz PUBLIC USE_OS_TZDB=0 )
+    endif()
+
+    if ( WIN32 AND BUILD_SHARED_LIBS )
+      target_compile_definitions( date-tz PUBLIC DATE_BUILD_DLL=1 )
+    endif()
+
+    set(TZ_HEADERS include/date/tz.h)
+
+    if( IOS )
+        list(APPEND TZ_HEADERS include/date/ios.h)
+    endif( )
+    set_target_properties( date-tz PROPERTIES
+        POSITION_INDEPENDENT_CODE ON
+        PUBLIC_HEADER "${TZ_HEADERS}"
+        VERSION "${PROJECT_VERSION}"
+        SOVERSION "${ABI_VERSION}" )
+    if( NOT MSVC )
+        find_package( Threads )
+        target_link_libraries( date-tz PUBLIC Threads::Threads )
+    endif( )
+    if( NOT USE_SYSTEM_TZ_DB AND NOT MANUAL_TZ_DB )
+        find_package( CURL REQUIRED )
+        target_include_directories( date-tz SYSTEM PRIVATE ${CURL_INCLUDE_DIRS} )
+        target_link_libraries( date-tz PRIVATE ${CURL_LIBRARIES} )
+    endif( )
+endif( )
+
+#[===================================================================[
+   installation
+#]===================================================================]
+set( version_config "${CMAKE_CURRENT_BINARY_DIR}/dateConfigVersion.cmake" )
+
+include( CMakePackageConfigHelpers )
+write_basic_package_version_file( "${version_config}"
+    VERSION ${PROJECT_VERSION}
+    COMPATIBILITY SameMajorVersion )
+
+install( TARGETS date
+    EXPORT dateConfig
+    PUBLIC_HEADER DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}/date )
+export( TARGETS date NAMESPACE date:: FILE dateTargets.cmake )
+if (CMAKE_VERSION VERSION_LESS 3.15)
+    install(
+        FILES include/date/date.h
+        DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}/date )
+endif ()
+
+if( BUILD_TZ_LIB )
+    install( TARGETS date-tz
+        EXPORT dateConfig
+        PUBLIC_HEADER DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}/date
+        ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR}
+        LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
+        RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR} )  # This is for Windows
+    export( TARGETS date-tz NAMESPACE date:: APPEND FILE dateTargets.cmake )
+endif( )
+
+if( WIN32 AND NOT CYGWIN)
+    set( CONFIG_LOC CMake )
+else( )
+    set( CONFIG_LOC "${CMAKE_INSTALL_LIBDIR}/cmake/date" )
+endif( )
+install( EXPORT dateConfig
+  FILE dateTargets.cmake
+  NAMESPACE date::
+  DESTINATION ${CONFIG_LOC} )
+install (
+  FILES cmake/dateConfig.cmake "${version_config}"
+  DESTINATION ${CONFIG_LOC})
+
+#[===================================================================[
+   testing
+#]===================================================================]
+if( ENABLE_DATE_TESTING )
+    enable_testing( )
+
+    add_custom_target( testit COMMAND ${CMAKE_CTEST_COMMAND} )
+    add_dependencies( testit date-tz )
+
+    function( add_pass_tests TEST_GLOB TEST_PREFIX )
+        file( GLOB_RECURSE FILENAMES ${TEST_GLOB} )
+
+        foreach( TEST_FILE ${FILENAMES} )
+            get_filename_component( TEST_NAME ${TEST_FILE} NAME_WE )
+            get_filename_component( TEST_EXT ${TEST_FILE} EXT )
+            if( NOT ${TEST_EXT} STREQUAL ".fail.cpp" )
+                set( PREFIX "${TEST_PREFIX}_pass_${TEST_NAME}" )
+                set( BIN_NAME ${PREFIX}_bin )
+                set( TST_NAME ${PREFIX}_test )
+                add_executable( ${BIN_NAME} EXCLUDE_FROM_ALL ${TEST_FILE} )
+                add_test( ${TST_NAME} ${BIN_NAME} )
+                target_link_libraries( ${BIN_NAME} date-tz )
+                # HACK: because the test files don't use FQ includes:
+                target_include_directories( ${BIN_NAME} PRIVATE include/date )
+                add_dependencies( testit ${BIN_NAME} )
+            endif( )
+        endforeach( )
+    endfunction( )
+
+    function( add_fail_tests TEST_GLOB TEST_PREFIX )
+        file( GLOB_RECURSE FILENAMES ${TEST_GLOB} )
+
+        foreach( TEST_FILE ${FILENAMES} )
+            get_filename_component( TEST_NAME ${TEST_FILE} NAME_WE )
+            get_filename_component( TEST_EXT ${TEST_FILE} EXT )
+
+            set( TEST_TYPE "_fail" )
+
+            set( PREFIX "${TEST_PREFIX}_fail_${TEST_NAME}" )
+            set( BIN_NAME ${PREFIX}_bin )
+            set( TST_NAME ${PREFIX}_test )
+
+            set( TEST_BIN_NAME ${CMAKE_BINARY_DIR}/${BIN_NAME} )
+            add_custom_target( ${BIN_NAME}
+                COMMAND
+                    ${PROJECT_SOURCE_DIR}/compile_fail.sh
+                    ${TEST_BIN_NAME}
+                    ${CMAKE_CXX_COMPILER}
+                    -std=c++14
+                    -L${CMAKE_BINARY_DIR}/
+                    -ldate-tz
+                    -I${PROJECT_SOURCE_DIR}/include
+                    -I${PROJECT_SOURCE_DIR}/include/date
+                    -o ${BIN_NAME}
+                    ${TEST_FILE}
+                WORKING_DIRECTORY ${CMAKE_BINARY_DIR}
+                COMMENT ${TST_NAME} )
+            add_test( ${TST_NAME} "${PROJECT_SOURCE_DIR}/test_fail.sh" ${CMAKE_BINARY_DIR}/${BIN_NAME} WORKING_DIRECTORY "${PROJECT_SOURCE_DIR}/" )
+            #set_tests_properties( ${TST_NAME} PROPERTIES WILL_FAIL TRUE)
+            add_dependencies( testit ${BIN_NAME} )
+        endforeach( )
+    endfunction( )
+
+    file( GLOB children RELATIVE "${PROJECT_SOURCE_DIR}/test" "${PROJECT_SOURCE_DIR}/test/*" )
+    foreach( child ${children} )
+        if( IS_DIRECTORY "${PROJECT_SOURCE_DIR}/test/${child}" )
+            set( CUR_FOLDER "${PROJECT_SOURCE_DIR}/test/${child}" )
+            add_pass_tests( "${CUR_FOLDER}/*.cpp" ${child} )
+            if( NOT WIN32 )
+                add_fail_tests( "${CUR_FOLDER}/*.fail.cpp" ${child} )
+            endif( )
+        endif( )
+    endforeach( )
+endif( )
diff --git a/third_party/date-3.0.1/LICENSE.txt b/third_party/date-3.0.1/LICENSE.txt
new file mode 100644
index 00000000..79ea0698
--- /dev/null
+++ b/third_party/date-3.0.1/LICENSE.txt
@@ -0,0 +1,31 @@
+The source code in this project is released using the MIT License. There is no
+global license for the project because each file is licensed individually with
+different author names and/or dates.
+
+If you contribute to this project, please add your name to the license of each
+file you modify.  If you have already contributed to this project and forgot to
+add your name to the license, please feel free to submit a new P/R to add your
+name to the license in each file you modified.
+
+For convenience, here is a copy of the MIT license found in each file except
+without author names or dates:
+
+The MIT License (MIT)
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
diff --git a/third_party/date-3.0.1/README.md b/third_party/date-3.0.1/README.md
new file mode 100644
index 00000000..7ef280f1
--- /dev/null
+++ b/third_party/date-3.0.1/README.md
@@ -0,0 +1,84 @@
+# Date
+
+[![Build Status](https://travis-ci.org/HowardHinnant/date.svg?branch=master)](https://travis-ci.org/HowardHinnant/date)
+[![Join the chat at https://gitter.im/HowardHinnant/date](https://badges.gitter.im/HowardHinnant/date.svg)](https://gitter.im/HowardHinnant/date?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
+
+---
+
+**[Try it out on wandbox!](https://wandbox.org/permlink/oyXjibyF680HHoyS)**
+
+## Summary
+
+This is actually several separate C++11/C++14/C++17 libraries:
+
+1. `"date.h"` is a header-only library which builds upon `<chrono>`.  It adds some new `duration` types, and new `time_point` types.  It also adds "field" types such as `year_month_day` which is a struct `{year, month, day}`.  And it provides convenient means to convert between the "field" types and the `time_point` types.
+
+    * Documentation: http://howardhinnant.github.io/date/date.html
+    * Video: https://www.youtube.com/watch?v=tzyGjOm8AKo
+    * Slides: http://schd.ws/hosted_files/cppcon2015/43/hinnant_dates.pdf
+
+1. `"tz.h"` / `"tz.cpp"`  are a timezone library built on top of the `"date.h"` library.  This timezone library is a complete parser of the IANA timezone database.  It provides for an easy way to access all of the data in this database, using the types from `"date.h"` and `<chrono>`.  The IANA database also includes data on leap seconds, and this library provides utilities to compute with that information as well.
+
+    * Documentation: http://howardhinnant.github.io/date/tz.html
+    * Video: https://www.youtube.com/watch?v=Vwd3pduVGKY
+    * Slides: http://schd.ws/hosted_files/cppcon2016/0f/Welcome%20To%20The%20Time%20Zone%20-%20Howard%20Hinnant%20-%20CppCon%202016.pdf
+
+1. `"iso_week.h"` is a header-only library built on top of the `"date.h"` library which implements the ISO week date calendar.
+
+    * Documentation: http://howardhinnant.github.io/date/iso_week.html
+
+1. `"julian.h"` is a header-only library built on top of the `"date.h"` library which implements a proleptic Julian calendar which is fully interoperable with everything above.
+
+    * Documentation: http://howardhinnant.github.io/date/julian.html
+
+1. `"islamic.h"` is a header-only library built on top of the `"date.h"` library which implements a proleptic Islamic calendar which is fully interoperable with everything above.
+
+    * Documentation: http://howardhinnant.github.io/date/islamic.html
+
+## Standardization
+
+Slightly modified versions of `"date.h"` and `"tz.h"` were voted into the C++20 working draft at the Jacksonville FL meeting on 2018-03-17:
+
+* http://howardhinnant.github.io/date/d0355r7.html
+
+## Build & Test
+
+The recommended way to use any of these libraries besides `"tz.h"` is to just include it.  These are header-only libraries (except `"tz.h"`).
+
+To use `"tz.h"`, there is a single source file (`src/tz.cpp`) that needs to be compiled. Here are the recommended directions:  https://howardhinnant.github.io/date/tz.html#Installation.
+
+One can run tests by cd'ing into the `test` subdirectory and running `testit`.  There are known failures on all platforms except for macOS.  And even on macOS if C++11 is used.  If any of these failures present problems for you, there exist workarounds.
+
+Additionally there is _unsupported_ support for [vcpkg](https://github.com/Microsoft/vcpkg) and [CMake](https://cmake.org/).  I don't personally use or maintain these systems as for me they cause more problems than they solve (for this small project).  If you would like to contribute to these build systems please feel free to file a PR.
+
+You can download and install Date using the [vcpkg](https://github.com/Microsoft/vcpkg) dependency manager:
+
+    git clone https://github.com/Microsoft/vcpkg.git
+    cd vcpkg
+    ./bootstrap-vcpkg.sh
+    ./vcpkg integrate install
+    vcpkg install date
+
+The Date port in vcpkg is updated by Microsoft team members and community contributors. If the version falls behind, please [create an issue or pull request](https://github.com/Microsoft/vcpkg) on the vcpkg repository.
+
+You can optionally build using [CMake](https://cmake.org/). Here is a guide of how to build and test using the CMake Makefile generator.
+
+```bash
+mkdir build
+cd build
+cmake -DENABLE_DATE_TESTING=ON -DBUILD_TZ_LIB=ON ../
+cmake --build . --target testit # Consider '-- -j4' for multithreading
+```
+## Projects using this library
+
+* www.safe.com
+* www.webtoolkit.eu/wt
+* https://github.com/ViewTouch/viewtouch
+* https://routinghub.com
+* https://github.com/valhalla
+* https://github.com/siodb/siodb
+* https://github.com/KomodoPlatform/atomicDEX-Pro
+* https://github.com/Kotlin/kotlinx-datetime
+* https://github.com/royalbee/jewish_date
+
+If you would like your project (or product) on this list, just let me know.
diff --git a/third_party/date-3.0.1/ci/install_cmake.sh b/third_party/date-3.0.1/ci/install_cmake.sh
new file mode 100644
index 00000000..2c9fa10d
--- /dev/null
+++ b/third_party/date-3.0.1/ci/install_cmake.sh
@@ -0,0 +1,34 @@
+#!/usr/bin/env bash
+set -e
+
+IFS=. read cm_maj cm_min cm_rel <<<"$1"
+: ${cm_rel:-0}
+CMAKE_ROOT=${2:-"${HOME}/cmake"}
+
+function cmake_version ()
+{
+    if [[ -d ${CMAKE_ROOT} ]] ; then
+        local perms=$(test $(uname) = "Linux" && echo "/111" || echo "+111")
+        local installed=$(find ${CMAKE_ROOT} -perm ${perms} -type f -name cmake)
+        if [[ "${installed}" != "" ]] ; then
+            echo "$(${installed} --version | head -1)"
+        fi
+    fi
+}
+
+installed=$(cmake_version)
+if [[ "${installed}" != "" && ${installed} =~ ${cm_maj}.${cm_min}.${cm_rel} ]] ; then
+    echo "cmake already installed: ${installed}"
+    exit
+fi
+
+pkgname="cmake-${cm_maj}.${cm_min}.${cm_rel}-$(uname)-x86_64.tar.gz"
+tmppkg="/tmp/cmake.tar.gz"
+wget --quiet https://cmake.org/files/v${cm_maj}.${cm_min}/${pkgname} -O ${tmppkg}
+mkdir -p ${CMAKE_ROOT}
+cd ${CMAKE_ROOT}
+tar --strip-components 1 -xf ${tmppkg}
+rm -f ${tmppkg}
+echo "installed: $(cmake_version)"
+
+
diff --git a/third_party/date-3.0.1/cmake/dateConfig.cmake b/third_party/date-3.0.1/cmake/dateConfig.cmake
new file mode 100644
index 00000000..2198ad1a
--- /dev/null
+++ b/third_party/date-3.0.1/cmake/dateConfig.cmake
@@ -0,0 +1,11 @@
+include( CMakeFindDependencyMacro )
+include( "${CMAKE_CURRENT_LIST_DIR}/dateTargets.cmake" )
+if( NOT MSVC AND TARGET date::date-tz )
+    find_dependency( Threads REQUIRED)
+    get_target_property( _tzill date::date-tz  INTERFACE_LINK_LIBRARIES )
+    if( _tzill AND "${_tzill}" MATCHES "libcurl" )
+        find_dependency( CURL )
+    endif( )
+endif( )
+
+
diff --git a/third_party/date-3.0.1/compile_fail.sh b/third_party/date-3.0.1/compile_fail.sh
new file mode 100644
index 00000000..60cf6b99
--- /dev/null
+++ b/third_party/date-3.0.1/compile_fail.sh
@@ -0,0 +1,16 @@
+#!/bin/bash
+export TEST_BIN_NAME=$1
+#echo "Building ${TEST_BIN_NAME}"
+shift 1
+export BUILD_COMMAND=$@
+#echo "Build command: ${BUILD_COMMAND}"
+eval ${BUILD_COMMAND} >/dev/null 2>/dev/null
+
+if [ $? -eq 0 ]; then
+	echo -ne "#!/bin/bash\nexit 1;" > ${TEST_BIN_NAME}
+else
+	echo -ne "#!/bin/bash\nexit 0;" > ${TEST_BIN_NAME}
+fi
+chmod u+x ${TEST_BIN_NAME}
+exit 0;
+
diff --git a/third_party/date-3.0.1/include/date/chrono_io.h b/third_party/date-3.0.1/include/date/chrono_io.h
new file mode 100644
index 00000000..21be4040
--- /dev/null
+++ b/third_party/date-3.0.1/include/date/chrono_io.h
@@ -0,0 +1,34 @@
+#ifndef CHRONO_IO_H
+#define CHRONO_IO_H
+
+// The MIT License (MIT)
+//
+// Copyright (c) 2016, 2017 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+//
+// Our apologies.  When the previous paragraph was written, lowercase had not yet
+// been invented (that would involve another several millennia of evolution).
+// We did not mean to shout.
+
+// This functionality has moved to "date.h"
+
+#include "date.h"
+
+#endif  // CHRONO_IO_H
diff --git a/third_party/date-3.0.1/include/date/date.h b/third_party/date-3.0.1/include/date/date.h
new file mode 100644
index 00000000..7b6b4e4c
--- /dev/null
+++ b/third_party/date-3.0.1/include/date/date.h
@@ -0,0 +1,8200 @@
+#ifndef DATE_H
+#define DATE_H
+
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016, 2017 Howard Hinnant
+// Copyright (c) 2016 Adrian Colomitchi
+// Copyright (c) 2017 Florian Dang
+// Copyright (c) 2017 Paul Thompson
+// Copyright (c) 2018, 2019 Tomasz Kamiński
+// Copyright (c) 2019 Jiangang Zhuang
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+//
+// Our apologies.  When the previous paragraph was written, lowercase had not yet
+// been invented (that would involve another several millennia of evolution).
+// We did not mean to shout.
+
+#ifndef HAS_STRING_VIEW
+#  if __cplusplus >= 201703 || (defined(_MSVC_LANG) && _MSVC_LANG >= 201703L)
+#    define HAS_STRING_VIEW 1
+#  else
+#    define HAS_STRING_VIEW 0
+#  endif
+#endif  // HAS_STRING_VIEW
+
+#include <cassert>
+#include <algorithm>
+#include <cctype>
+#include <chrono>
+#include <climits>
+#include <cmath>
+#include <cstddef>
+#include <cstdint>
+#include <cstdlib>
+#include <ctime>
+#include <ios>
+#include <istream>
+#include <iterator>
+#include <limits>
+#include <locale>
+#include <memory>
+#include <ostream>
+#include <ratio>
+#include <sstream>
+#include <stdexcept>
+#include <string>
+#if HAS_STRING_VIEW
+# include <string_view>
+#endif
+#include <utility>
+#include <type_traits>
+
+#ifdef __GNUC__
+# pragma GCC diagnostic push
+# if __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ > 7)
+#  pragma GCC diagnostic ignored "-Wpedantic"
+# endif
+# if __GNUC__ < 5
+   // GCC 4.9 Bug 61489 Wrong warning with -Wmissing-field-initializers
+#  pragma GCC diagnostic ignored "-Wmissing-field-initializers"
+# endif
+#endif
+
+#ifdef _MSC_VER
+#   pragma warning(push)
+// warning C4127: conditional expression is constant
+#   pragma warning(disable : 4127)
+#endif
+
+namespace date
+{
+
+//---------------+
+// Configuration |
+//---------------+
+
+#ifndef ONLY_C_LOCALE
+#  define ONLY_C_LOCALE 0
+#endif
+
+#if defined(_MSC_VER) && (!defined(__clang__) || (_MSC_VER < 1910))
+// MSVC
+#  ifndef _SILENCE_CXX17_UNCAUGHT_EXCEPTION_DEPRECATION_WARNING
+#    define _SILENCE_CXX17_UNCAUGHT_EXCEPTION_DEPRECATION_WARNING
+#  endif
+#  if _MSC_VER < 1910
+//   before VS2017
+#    define CONSTDATA const
+#    define CONSTCD11
+#    define CONSTCD14
+#    define NOEXCEPT _NOEXCEPT
+#  else
+//   VS2017 and later
+#    define CONSTDATA constexpr const
+#    define CONSTCD11 constexpr
+#    define CONSTCD14 constexpr
+#    define NOEXCEPT noexcept
+#  endif
+
+#elif defined(__SUNPRO_CC) && __SUNPRO_CC <= 0x5150
+// Oracle Developer Studio 12.6 and earlier
+#  define CONSTDATA constexpr const
+#  define CONSTCD11 constexpr
+#  define CONSTCD14
+#  define NOEXCEPT noexcept
+
+#elif __cplusplus >= 201402
+// C++14
+#  define CONSTDATA constexpr const
+#  define CONSTCD11 constexpr
+#  define CONSTCD14 constexpr
+#  define NOEXCEPT noexcept
+#else
+// C++11
+#  define CONSTDATA constexpr const
+#  define CONSTCD11 constexpr
+#  define CONSTCD14
+#  define NOEXCEPT noexcept
+#endif
+
+#ifndef HAS_UNCAUGHT_EXCEPTIONS
+#  if __cplusplus >= 201703 || (defined(_MSVC_LANG) && _MSVC_LANG >= 201703L)
+#    define HAS_UNCAUGHT_EXCEPTIONS 1
+#  else
+#    define HAS_UNCAUGHT_EXCEPTIONS 0
+#  endif
+#endif  // HAS_UNCAUGHT_EXCEPTIONS
+
+#ifndef HAS_VOID_T
+#  if __cplusplus >= 201703 || (defined(_MSVC_LANG) && _MSVC_LANG >= 201703L)
+#    define HAS_VOID_T 1
+#  else
+#    define HAS_VOID_T 0
+#  endif
+#endif  // HAS_VOID_T
+
+// Protect from Oracle sun macro
+#ifdef sun
+#  undef sun
+#endif
+
+// Work around for a NVCC compiler bug which causes it to fail
+// to compile std::ratio_{multiply,divide} when used directly
+// in the std::chrono::duration template instantiations below
+namespace detail {
+template <typename R1, typename R2>
+using ratio_multiply = decltype(std::ratio_multiply<R1, R2>{});
+
+template <typename R1, typename R2>
+using ratio_divide = decltype(std::ratio_divide<R1, R2>{});
+}  // namespace detail
+
+//-----------+
+// Interface |
+//-----------+
+
+// durations
+
+using days = std::chrono::duration
+    <int, detail::ratio_multiply<std::ratio<24>, std::chrono::hours::period>>;
+
+using weeks = std::chrono::duration
+    <int, detail::ratio_multiply<std::ratio<7>, days::period>>;
+
+using years = std::chrono::duration
+    <int, detail::ratio_multiply<std::ratio<146097, 400>, days::period>>;
+
+using months = std::chrono::duration
+    <int, detail::ratio_divide<years::period, std::ratio<12>>>;
+
+// time_point
+
+template <class Duration>
+    using sys_time = std::chrono::time_point<std::chrono::system_clock, Duration>;
+
+using sys_days    = sys_time<days>;
+using sys_seconds = sys_time<std::chrono::seconds>;
+
+struct local_t {};
+
+template <class Duration>
+    using local_time = std::chrono::time_point<local_t, Duration>;
+
+using local_seconds = local_time<std::chrono::seconds>;
+using local_days    = local_time<days>;
+
+// types
+
+struct last_spec
+{
+    explicit last_spec() = default;
+};
+
+class day;
+class month;
+class year;
+
+class weekday;
+class weekday_indexed;
+class weekday_last;
+
+class month_day;
+class month_day_last;
+class month_weekday;
+class month_weekday_last;
+
+class year_month;
+
+class year_month_day;
+class year_month_day_last;
+class year_month_weekday;
+class year_month_weekday_last;
+
+// date composition operators
+
+CONSTCD11 year_month operator/(const year& y, const month& m) NOEXCEPT;
+CONSTCD11 year_month operator/(const year& y, int          m) NOEXCEPT;
+
+CONSTCD11 month_day operator/(const day& d, const month& m) NOEXCEPT;
+CONSTCD11 month_day operator/(const day& d, int          m) NOEXCEPT;
+CONSTCD11 month_day operator/(const month& m, const day& d) NOEXCEPT;
+CONSTCD11 month_day operator/(const month& m, int        d) NOEXCEPT;
+CONSTCD11 month_day operator/(int          m, const day& d) NOEXCEPT;
+
+CONSTCD11 month_day_last operator/(const month& m, last_spec) NOEXCEPT;
+CONSTCD11 month_day_last operator/(int          m, last_spec) NOEXCEPT;
+CONSTCD11 month_day_last operator/(last_spec, const month& m) NOEXCEPT;
+CONSTCD11 month_day_last operator/(last_spec, int          m) NOEXCEPT;
+
+CONSTCD11 month_weekday operator/(const month& m, const weekday_indexed& wdi) NOEXCEPT;
+CONSTCD11 month_weekday operator/(int          m, const weekday_indexed& wdi) NOEXCEPT;
+CONSTCD11 month_weekday operator/(const weekday_indexed& wdi, const month& m) NOEXCEPT;
+CONSTCD11 month_weekday operator/(const weekday_indexed& wdi, int          m) NOEXCEPT;
+
+CONSTCD11 month_weekday_last operator/(const month& m, const weekday_last& wdl) NOEXCEPT;
+CONSTCD11 month_weekday_last operator/(int          m, const weekday_last& wdl) NOEXCEPT;
+CONSTCD11 month_weekday_last operator/(const weekday_last& wdl, const month& m) NOEXCEPT;
+CONSTCD11 month_weekday_last operator/(const weekday_last& wdl, int          m) NOEXCEPT;
+
+CONSTCD11 year_month_day operator/(const year_month& ym, const day& d) NOEXCEPT;
+CONSTCD11 year_month_day operator/(const year_month& ym, int        d) NOEXCEPT;
+CONSTCD11 year_month_day operator/(const year& y, const month_day& md) NOEXCEPT;
+CONSTCD11 year_month_day operator/(int         y, const month_day& md) NOEXCEPT;
+CONSTCD11 year_month_day operator/(const month_day& md, const year& y) NOEXCEPT;
+CONSTCD11 year_month_day operator/(const month_day& md, int         y) NOEXCEPT;
+
+CONSTCD11
+    year_month_day_last operator/(const year_month& ym,   last_spec) NOEXCEPT;
+CONSTCD11
+    year_month_day_last operator/(const year& y, const month_day_last& mdl) NOEXCEPT;
+CONSTCD11
+    year_month_day_last operator/(int         y, const month_day_last& mdl) NOEXCEPT;
+CONSTCD11
+    year_month_day_last operator/(const month_day_last& mdl, const year& y) NOEXCEPT;
+CONSTCD11
+    year_month_day_last operator/(const month_day_last& mdl, int         y) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday
+operator/(const year_month& ym, const weekday_indexed& wdi) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday
+operator/(const year&        y, const month_weekday&   mwd) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday
+operator/(int                y, const month_weekday&   mwd) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday
+operator/(const month_weekday& mwd, const year&          y) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday
+operator/(const month_weekday& mwd, int                  y) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday_last
+operator/(const year_month& ym, const weekday_last& wdl) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday_last
+operator/(const year& y, const month_weekday_last& mwdl) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday_last
+operator/(int         y, const month_weekday_last& mwdl) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday_last
+operator/(const month_weekday_last& mwdl, const year& y) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday_last
+operator/(const month_weekday_last& mwdl, int         y) NOEXCEPT;
+
+// Detailed interface
+
+// day
+
+class day
+{
+    unsigned char d_;
+
+public:
+    day() = default;
+    explicit CONSTCD11 day(unsigned d) NOEXCEPT;
+
+    CONSTCD14 day& operator++()    NOEXCEPT;
+    CONSTCD14 day  operator++(int) NOEXCEPT;
+    CONSTCD14 day& operator--()    NOEXCEPT;
+    CONSTCD14 day  operator--(int) NOEXCEPT;
+
+    CONSTCD14 day& operator+=(const days& d) NOEXCEPT;
+    CONSTCD14 day& operator-=(const days& d) NOEXCEPT;
+
+    CONSTCD11 explicit operator unsigned() const NOEXCEPT;
+    CONSTCD11 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const day& x, const day& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const day& x, const day& y) NOEXCEPT;
+CONSTCD11 bool operator< (const day& x, const day& y) NOEXCEPT;
+CONSTCD11 bool operator> (const day& x, const day& y) NOEXCEPT;
+CONSTCD11 bool operator<=(const day& x, const day& y) NOEXCEPT;
+CONSTCD11 bool operator>=(const day& x, const day& y) NOEXCEPT;
+
+CONSTCD11 day  operator+(const day&  x, const days& y) NOEXCEPT;
+CONSTCD11 day  operator+(const days& x, const day&  y) NOEXCEPT;
+CONSTCD11 day  operator-(const day&  x, const days& y) NOEXCEPT;
+CONSTCD11 days operator-(const day&  x, const day&  y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const day& d);
+
+// month
+
+class month
+{
+    unsigned char m_;
+
+public:
+    month() = default;
+    explicit CONSTCD11 month(unsigned m) NOEXCEPT;
+
+    CONSTCD14 month& operator++()    NOEXCEPT;
+    CONSTCD14 month  operator++(int) NOEXCEPT;
+    CONSTCD14 month& operator--()    NOEXCEPT;
+    CONSTCD14 month  operator--(int) NOEXCEPT;
+
+    CONSTCD14 month& operator+=(const months& m) NOEXCEPT;
+    CONSTCD14 month& operator-=(const months& m) NOEXCEPT;
+
+    CONSTCD11 explicit operator unsigned() const NOEXCEPT;
+    CONSTCD11 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const month& x, const month& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const month& x, const month& y) NOEXCEPT;
+CONSTCD11 bool operator< (const month& x, const month& y) NOEXCEPT;
+CONSTCD11 bool operator> (const month& x, const month& y) NOEXCEPT;
+CONSTCD11 bool operator<=(const month& x, const month& y) NOEXCEPT;
+CONSTCD11 bool operator>=(const month& x, const month& y) NOEXCEPT;
+
+CONSTCD14 month  operator+(const month&  x, const months& y) NOEXCEPT;
+CONSTCD14 month  operator+(const months& x,  const month& y) NOEXCEPT;
+CONSTCD14 month  operator-(const month&  x, const months& y) NOEXCEPT;
+CONSTCD14 months operator-(const month&  x,  const month& y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const month& m);
+
+// year
+
+class year
+{
+    short y_;
+
+public:
+    year() = default;
+    explicit CONSTCD11 year(int y) NOEXCEPT;
+
+    CONSTCD14 year& operator++()    NOEXCEPT;
+    CONSTCD14 year  operator++(int) NOEXCEPT;
+    CONSTCD14 year& operator--()    NOEXCEPT;
+    CONSTCD14 year  operator--(int) NOEXCEPT;
+
+    CONSTCD14 year& operator+=(const years& y) NOEXCEPT;
+    CONSTCD14 year& operator-=(const years& y) NOEXCEPT;
+
+    CONSTCD11 year operator-() const NOEXCEPT;
+    CONSTCD11 year operator+() const NOEXCEPT;
+
+    CONSTCD11 bool is_leap() const NOEXCEPT;
+
+    CONSTCD11 explicit operator int() const NOEXCEPT;
+    CONSTCD11 bool ok() const NOEXCEPT;
+
+    static CONSTCD11 year min() NOEXCEPT { return year{-32767}; }
+    static CONSTCD11 year max() NOEXCEPT { return year{32767}; }
+};
+
+CONSTCD11 bool operator==(const year& x, const year& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const year& x, const year& y) NOEXCEPT;
+CONSTCD11 bool operator< (const year& x, const year& y) NOEXCEPT;
+CONSTCD11 bool operator> (const year& x, const year& y) NOEXCEPT;
+CONSTCD11 bool operator<=(const year& x, const year& y) NOEXCEPT;
+CONSTCD11 bool operator>=(const year& x, const year& y) NOEXCEPT;
+
+CONSTCD11 year  operator+(const year&  x, const years& y) NOEXCEPT;
+CONSTCD11 year  operator+(const years& x, const year&  y) NOEXCEPT;
+CONSTCD11 year  operator-(const year&  x, const years& y) NOEXCEPT;
+CONSTCD11 years operator-(const year&  x, const year&  y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year& y);
+
+// weekday
+
+class weekday
+{
+    unsigned char wd_;
+public:
+    weekday() = default;
+    explicit CONSTCD11 weekday(unsigned wd) NOEXCEPT;
+    CONSTCD14 weekday(const sys_days& dp) NOEXCEPT;
+    CONSTCD14 explicit weekday(const local_days& dp) NOEXCEPT;
+
+    CONSTCD14 weekday& operator++()    NOEXCEPT;
+    CONSTCD14 weekday  operator++(int) NOEXCEPT;
+    CONSTCD14 weekday& operator--()    NOEXCEPT;
+    CONSTCD14 weekday  operator--(int) NOEXCEPT;
+
+    CONSTCD14 weekday& operator+=(const days& d) NOEXCEPT;
+    CONSTCD14 weekday& operator-=(const days& d) NOEXCEPT;
+
+    CONSTCD11 bool ok() const NOEXCEPT;
+
+    CONSTCD11 unsigned c_encoding() const NOEXCEPT;
+    CONSTCD11 unsigned iso_encoding() const NOEXCEPT;
+
+    CONSTCD11 weekday_indexed operator[](unsigned index) const NOEXCEPT;
+    CONSTCD11 weekday_last    operator[](last_spec)      const NOEXCEPT;
+
+private:
+    static CONSTCD14 unsigned char weekday_from_days(int z) NOEXCEPT;
+
+    friend CONSTCD11 bool operator==(const weekday& x, const weekday& y) NOEXCEPT;
+    friend CONSTCD14 days operator-(const weekday& x, const weekday& y) NOEXCEPT;
+    friend CONSTCD14 weekday operator+(const weekday& x, const days& y) NOEXCEPT;
+    template<class CharT, class Traits>
+        friend std::basic_ostream<CharT, Traits>&
+            operator<<(std::basic_ostream<CharT, Traits>& os, const weekday& wd);
+    friend class weekday_indexed;
+};
+
+CONSTCD11 bool operator==(const weekday& x, const weekday& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const weekday& x, const weekday& y) NOEXCEPT;
+
+CONSTCD14 weekday operator+(const weekday& x, const days&    y) NOEXCEPT;
+CONSTCD14 weekday operator+(const days&    x, const weekday& y) NOEXCEPT;
+CONSTCD14 weekday operator-(const weekday& x, const days&    y) NOEXCEPT;
+CONSTCD14 days    operator-(const weekday& x, const weekday& y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const weekday& wd);
+
+// weekday_indexed
+
+class weekday_indexed
+{
+    unsigned char wd_    : 4;
+    unsigned char index_ : 4;
+
+public:
+    weekday_indexed() = default;
+    CONSTCD11 weekday_indexed(const date::weekday& wd, unsigned index) NOEXCEPT;
+
+    CONSTCD11 date::weekday weekday() const NOEXCEPT;
+    CONSTCD11 unsigned index() const NOEXCEPT;
+    CONSTCD11 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const weekday_indexed& x, const weekday_indexed& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const weekday_indexed& x, const weekday_indexed& y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const weekday_indexed& wdi);
+
+// weekday_last
+
+class weekday_last
+{
+    date::weekday wd_;
+
+public:
+    explicit CONSTCD11 weekday_last(const date::weekday& wd) NOEXCEPT;
+
+    CONSTCD11 date::weekday weekday() const NOEXCEPT;
+    CONSTCD11 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const weekday_last& x, const weekday_last& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const weekday_last& x, const weekday_last& y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const weekday_last& wdl);
+
+namespace detail
+{
+
+struct unspecified_month_disambiguator {};
+
+}  // namespace detail
+
+// year_month
+
+class year_month
+{
+    date::year  y_;
+    date::month m_;
+
+public:
+    year_month() = default;
+    CONSTCD11 year_month(const date::year& y, const date::month& m) NOEXCEPT;
+
+    CONSTCD11 date::year  year()  const NOEXCEPT;
+    CONSTCD11 date::month month() const NOEXCEPT;
+
+    template<class = detail::unspecified_month_disambiguator>
+    CONSTCD14 year_month& operator+=(const months& dm) NOEXCEPT;
+    template<class = detail::unspecified_month_disambiguator>
+    CONSTCD14 year_month& operator-=(const months& dm) NOEXCEPT;
+    CONSTCD14 year_month& operator+=(const years& dy) NOEXCEPT;
+    CONSTCD14 year_month& operator-=(const years& dy) NOEXCEPT;
+
+    CONSTCD11 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const year_month& x, const year_month& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const year_month& x, const year_month& y) NOEXCEPT;
+CONSTCD11 bool operator< (const year_month& x, const year_month& y) NOEXCEPT;
+CONSTCD11 bool operator> (const year_month& x, const year_month& y) NOEXCEPT;
+CONSTCD11 bool operator<=(const year_month& x, const year_month& y) NOEXCEPT;
+CONSTCD11 bool operator>=(const year_month& x, const year_month& y) NOEXCEPT;
+
+template<class = detail::unspecified_month_disambiguator>
+CONSTCD14 year_month operator+(const year_month& ym, const months& dm) NOEXCEPT;
+template<class = detail::unspecified_month_disambiguator>
+CONSTCD14 year_month operator+(const months& dm, const year_month& ym) NOEXCEPT;
+template<class = detail::unspecified_month_disambiguator>
+CONSTCD14 year_month operator-(const year_month& ym, const months& dm) NOEXCEPT;
+
+CONSTCD11 months operator-(const year_month& x, const year_month& y) NOEXCEPT;
+CONSTCD11 year_month operator+(const year_month& ym, const years& dy) NOEXCEPT;
+CONSTCD11 year_month operator+(const years& dy, const year_month& ym) NOEXCEPT;
+CONSTCD11 year_month operator-(const year_month& ym, const years& dy) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_month& ym);
+
+// month_day
+
+class month_day
+{
+    date::month m_;
+    date::day   d_;
+
+public:
+    month_day() = default;
+    CONSTCD11 month_day(const date::month& m, const date::day& d) NOEXCEPT;
+
+    CONSTCD11 date::month month() const NOEXCEPT;
+    CONSTCD11 date::day   day() const NOEXCEPT;
+
+    CONSTCD14 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const month_day& x, const month_day& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const month_day& x, const month_day& y) NOEXCEPT;
+CONSTCD11 bool operator< (const month_day& x, const month_day& y) NOEXCEPT;
+CONSTCD11 bool operator> (const month_day& x, const month_day& y) NOEXCEPT;
+CONSTCD11 bool operator<=(const month_day& x, const month_day& y) NOEXCEPT;
+CONSTCD11 bool operator>=(const month_day& x, const month_day& y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const month_day& md);
+
+// month_day_last
+
+class month_day_last
+{
+    date::month m_;
+
+public:
+    CONSTCD11 explicit month_day_last(const date::month& m) NOEXCEPT;
+
+    CONSTCD11 date::month month() const NOEXCEPT;
+    CONSTCD11 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const month_day_last& x, const month_day_last& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const month_day_last& x, const month_day_last& y) NOEXCEPT;
+CONSTCD11 bool operator< (const month_day_last& x, const month_day_last& y) NOEXCEPT;
+CONSTCD11 bool operator> (const month_day_last& x, const month_day_last& y) NOEXCEPT;
+CONSTCD11 bool operator<=(const month_day_last& x, const month_day_last& y) NOEXCEPT;
+CONSTCD11 bool operator>=(const month_day_last& x, const month_day_last& y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const month_day_last& mdl);
+
+// month_weekday
+
+class month_weekday
+{
+    date::month           m_;
+    date::weekday_indexed wdi_;
+public:
+    CONSTCD11 month_weekday(const date::month& m,
+                            const date::weekday_indexed& wdi) NOEXCEPT;
+
+    CONSTCD11 date::month           month()           const NOEXCEPT;
+    CONSTCD11 date::weekday_indexed weekday_indexed() const NOEXCEPT;
+
+    CONSTCD11 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const month_weekday& x, const month_weekday& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const month_weekday& x, const month_weekday& y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const month_weekday& mwd);
+
+// month_weekday_last
+
+class month_weekday_last
+{
+    date::month        m_;
+    date::weekday_last wdl_;
+
+public:
+    CONSTCD11 month_weekday_last(const date::month& m,
+                                 const date::weekday_last& wd) NOEXCEPT;
+
+    CONSTCD11 date::month        month()        const NOEXCEPT;
+    CONSTCD11 date::weekday_last weekday_last() const NOEXCEPT;
+
+    CONSTCD11 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11
+    bool operator==(const month_weekday_last& x, const month_weekday_last& y) NOEXCEPT;
+CONSTCD11
+    bool operator!=(const month_weekday_last& x, const month_weekday_last& y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const month_weekday_last& mwdl);
+
+// class year_month_day
+
+class year_month_day
+{
+    date::year  y_;
+    date::month m_;
+    date::day   d_;
+
+public:
+    year_month_day() = default;
+    CONSTCD11 year_month_day(const date::year& y, const date::month& m,
+                             const date::day& d) NOEXCEPT;
+    CONSTCD14 year_month_day(const year_month_day_last& ymdl) NOEXCEPT;
+
+    CONSTCD14 year_month_day(sys_days dp) NOEXCEPT;
+    CONSTCD14 explicit year_month_day(local_days dp) NOEXCEPT;
+
+    template<class = detail::unspecified_month_disambiguator>
+    CONSTCD14 year_month_day& operator+=(const months& m) NOEXCEPT;
+    template<class = detail::unspecified_month_disambiguator>
+    CONSTCD14 year_month_day& operator-=(const months& m) NOEXCEPT;
+    CONSTCD14 year_month_day& operator+=(const years& y)  NOEXCEPT;
+    CONSTCD14 year_month_day& operator-=(const years& y)  NOEXCEPT;
+
+    CONSTCD11 date::year  year()  const NOEXCEPT;
+    CONSTCD11 date::month month() const NOEXCEPT;
+    CONSTCD11 date::day   day()   const NOEXCEPT;
+
+    CONSTCD14 operator sys_days() const NOEXCEPT;
+    CONSTCD14 explicit operator local_days() const NOEXCEPT;
+    CONSTCD14 bool ok() const NOEXCEPT;
+
+private:
+    static CONSTCD14 year_month_day from_days(days dp) NOEXCEPT;
+    CONSTCD14 days to_days() const NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const year_month_day& x, const year_month_day& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const year_month_day& x, const year_month_day& y) NOEXCEPT;
+CONSTCD11 bool operator< (const year_month_day& x, const year_month_day& y) NOEXCEPT;
+CONSTCD11 bool operator> (const year_month_day& x, const year_month_day& y) NOEXCEPT;
+CONSTCD11 bool operator<=(const year_month_day& x, const year_month_day& y) NOEXCEPT;
+CONSTCD11 bool operator>=(const year_month_day& x, const year_month_day& y) NOEXCEPT;
+
+template<class = detail::unspecified_month_disambiguator>
+CONSTCD14 year_month_day operator+(const year_month_day& ymd, const months& dm) NOEXCEPT;
+template<class = detail::unspecified_month_disambiguator>
+CONSTCD14 year_month_day operator+(const months& dm, const year_month_day& ymd) NOEXCEPT;
+template<class = detail::unspecified_month_disambiguator>
+CONSTCD14 year_month_day operator-(const year_month_day& ymd, const months& dm) NOEXCEPT;
+CONSTCD11 year_month_day operator+(const year_month_day& ymd, const years& dy)  NOEXCEPT;
+CONSTCD11 year_month_day operator+(const years& dy, const year_month_day& ymd)  NOEXCEPT;
+CONSTCD11 year_month_day operator-(const year_month_day& ymd, const years& dy)  NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_month_day& ymd);
+
+// year_month_day_last
+
+class year_month_day_last
+{
+    date::year           y_;
+    date::month_day_last mdl_;
+
+public:
+    CONSTCD11 year_month_day_last(const date::year& y,
+                                  const date::month_day_last& mdl) NOEXCEPT;
+
+    template<class = detail::unspecified_month_disambiguator>
+    CONSTCD14 year_month_day_last& operator+=(const months& m) NOEXCEPT;
+    template<class = detail::unspecified_month_disambiguator>
+    CONSTCD14 year_month_day_last& operator-=(const months& m) NOEXCEPT;
+    CONSTCD14 year_month_day_last& operator+=(const years& y)  NOEXCEPT;
+    CONSTCD14 year_month_day_last& operator-=(const years& y)  NOEXCEPT;
+
+    CONSTCD11 date::year           year()           const NOEXCEPT;
+    CONSTCD11 date::month          month()          const NOEXCEPT;
+    CONSTCD11 date::month_day_last month_day_last() const NOEXCEPT;
+    CONSTCD14 date::day            day()            const NOEXCEPT;
+
+    CONSTCD14 operator sys_days() const NOEXCEPT;
+    CONSTCD14 explicit operator local_days() const NOEXCEPT;
+    CONSTCD11 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11
+    bool operator==(const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT;
+CONSTCD11
+    bool operator!=(const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT;
+CONSTCD11
+    bool operator< (const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT;
+CONSTCD11
+    bool operator> (const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT;
+CONSTCD11
+    bool operator<=(const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT;
+CONSTCD11
+    bool operator>=(const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT;
+
+template<class = detail::unspecified_month_disambiguator>
+CONSTCD14
+year_month_day_last
+operator+(const year_month_day_last& ymdl, const months& dm) NOEXCEPT;
+
+template<class = detail::unspecified_month_disambiguator>
+CONSTCD14
+year_month_day_last
+operator+(const months& dm, const year_month_day_last& ymdl) NOEXCEPT;
+
+CONSTCD11
+year_month_day_last
+operator+(const year_month_day_last& ymdl, const years& dy) NOEXCEPT;
+
+CONSTCD11
+year_month_day_last
+operator+(const years& dy, const year_month_day_last& ymdl) NOEXCEPT;
+
+template<class = detail::unspecified_month_disambiguator>
+CONSTCD14
+year_month_day_last
+operator-(const year_month_day_last& ymdl, const months& dm) NOEXCEPT;
+
+CONSTCD11
+year_month_day_last
+operator-(const year_month_day_last& ymdl, const years& dy) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_month_day_last& ymdl);
+
+// year_month_weekday
+
+class year_month_weekday
+{
+    date::year            y_;
+    date::month           m_;
+    date::weekday_indexed wdi_;
+
+public:
+    year_month_weekday() = default;
+    CONSTCD11 year_month_weekday(const date::year& y, const date::month& m,
+                                   const date::weekday_indexed& wdi) NOEXCEPT;
+    CONSTCD14 year_month_weekday(const sys_days& dp) NOEXCEPT;
+    CONSTCD14 explicit year_month_weekday(const local_days& dp) NOEXCEPT;
+
+    template<class = detail::unspecified_month_disambiguator>
+    CONSTCD14 year_month_weekday& operator+=(const months& m) NOEXCEPT;
+    template<class = detail::unspecified_month_disambiguator>
+    CONSTCD14 year_month_weekday& operator-=(const months& m) NOEXCEPT;
+    CONSTCD14 year_month_weekday& operator+=(const years& y)  NOEXCEPT;
+    CONSTCD14 year_month_weekday& operator-=(const years& y)  NOEXCEPT;
+
+    CONSTCD11 date::year year() const NOEXCEPT;
+    CONSTCD11 date::month month() const NOEXCEPT;
+    CONSTCD11 date::weekday weekday() const NOEXCEPT;
+    CONSTCD11 unsigned index() const NOEXCEPT;
+    CONSTCD11 date::weekday_indexed weekday_indexed() const NOEXCEPT;
+
+    CONSTCD14 operator sys_days() const NOEXCEPT;
+    CONSTCD14 explicit operator local_days() const NOEXCEPT;
+    CONSTCD14 bool ok() const NOEXCEPT;
+
+private:
+    static CONSTCD14 year_month_weekday from_days(days dp) NOEXCEPT;
+    CONSTCD14 days to_days() const NOEXCEPT;
+};
+
+CONSTCD11
+    bool operator==(const year_month_weekday& x, const year_month_weekday& y) NOEXCEPT;
+CONSTCD11
+    bool operator!=(const year_month_weekday& x, const year_month_weekday& y) NOEXCEPT;
+
+template<class = detail::unspecified_month_disambiguator>
+CONSTCD14
+year_month_weekday
+operator+(const year_month_weekday& ymwd, const months& dm) NOEXCEPT;
+
+template<class = detail::unspecified_month_disambiguator>
+CONSTCD14
+year_month_weekday
+operator+(const months& dm, const year_month_weekday& ymwd) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday
+operator+(const year_month_weekday& ymwd, const years& dy) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday
+operator+(const years& dy, const year_month_weekday& ymwd) NOEXCEPT;
+
+template<class = detail::unspecified_month_disambiguator>
+CONSTCD14
+year_month_weekday
+operator-(const year_month_weekday& ymwd, const months& dm) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday
+operator-(const year_month_weekday& ymwd, const years& dy) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_month_weekday& ymwdi);
+
+// year_month_weekday_last
+
+class year_month_weekday_last
+{
+    date::year y_;
+    date::month m_;
+    date::weekday_last wdl_;
+
+public:
+    CONSTCD11 year_month_weekday_last(const date::year& y, const date::month& m,
+                                      const date::weekday_last& wdl) NOEXCEPT;
+
+    template<class = detail::unspecified_month_disambiguator>
+    CONSTCD14 year_month_weekday_last& operator+=(const months& m) NOEXCEPT;
+    template<class = detail::unspecified_month_disambiguator>
+    CONSTCD14 year_month_weekday_last& operator-=(const months& m) NOEXCEPT;
+    CONSTCD14 year_month_weekday_last& operator+=(const years& y) NOEXCEPT;
+    CONSTCD14 year_month_weekday_last& operator-=(const years& y) NOEXCEPT;
+
+    CONSTCD11 date::year year() const NOEXCEPT;
+    CONSTCD11 date::month month() const NOEXCEPT;
+    CONSTCD11 date::weekday weekday() const NOEXCEPT;
+    CONSTCD11 date::weekday_last weekday_last() const NOEXCEPT;
+
+    CONSTCD14 operator sys_days() const NOEXCEPT;
+    CONSTCD14 explicit operator local_days() const NOEXCEPT;
+    CONSTCD11 bool ok() const NOEXCEPT;
+
+private:
+    CONSTCD14 days to_days() const NOEXCEPT;
+};
+
+CONSTCD11
+bool
+operator==(const year_month_weekday_last& x, const year_month_weekday_last& y) NOEXCEPT;
+
+CONSTCD11
+bool
+operator!=(const year_month_weekday_last& x, const year_month_weekday_last& y) NOEXCEPT;
+
+template<class = detail::unspecified_month_disambiguator>
+CONSTCD14
+year_month_weekday_last
+operator+(const year_month_weekday_last& ymwdl, const months& dm) NOEXCEPT;
+
+template<class = detail::unspecified_month_disambiguator>
+CONSTCD14
+year_month_weekday_last
+operator+(const months& dm, const year_month_weekday_last& ymwdl) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday_last
+operator+(const year_month_weekday_last& ymwdl, const years& dy) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday_last
+operator+(const years& dy, const year_month_weekday_last& ymwdl) NOEXCEPT;
+
+template<class = detail::unspecified_month_disambiguator>
+CONSTCD14
+year_month_weekday_last
+operator-(const year_month_weekday_last& ymwdl, const months& dm) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday_last
+operator-(const year_month_weekday_last& ymwdl, const years& dy) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_month_weekday_last& ymwdl);
+
+#if !defined(_MSC_VER) || (_MSC_VER >= 1900)
+inline namespace literals
+{
+
+CONSTCD11 date::day  operator "" _d(unsigned long long d) NOEXCEPT;
+CONSTCD11 date::year operator "" _y(unsigned long long y) NOEXCEPT;
+
+}  // inline namespace literals
+#endif // !defined(_MSC_VER) || (_MSC_VER >= 1900)
+
+// CONSTDATA date::month January{1};
+// CONSTDATA date::month February{2};
+// CONSTDATA date::month March{3};
+// CONSTDATA date::month April{4};
+// CONSTDATA date::month May{5};
+// CONSTDATA date::month June{6};
+// CONSTDATA date::month July{7};
+// CONSTDATA date::month August{8};
+// CONSTDATA date::month September{9};
+// CONSTDATA date::month October{10};
+// CONSTDATA date::month November{11};
+// CONSTDATA date::month December{12};
+//
+// CONSTDATA date::weekday Sunday{0u};
+// CONSTDATA date::weekday Monday{1u};
+// CONSTDATA date::weekday Tuesday{2u};
+// CONSTDATA date::weekday Wednesday{3u};
+// CONSTDATA date::weekday Thursday{4u};
+// CONSTDATA date::weekday Friday{5u};
+// CONSTDATA date::weekday Saturday{6u};
+
+#if HAS_VOID_T
+
+template <class T, class = std::void_t<>>
+struct is_clock
+    : std::false_type
+{};
+
+template <class T>
+struct is_clock<T, std::void_t<decltype(T::now()), typename T::rep, typename T::period,
+                               typename T::duration, typename T::time_point,
+                               decltype(T::is_steady)>>
+    : std::true_type
+{};
+
+template<class T> inline constexpr bool is_clock_v = is_clock<T>::value;
+
+#endif  // HAS_VOID_T
+
+//----------------+
+// Implementation |
+//----------------+
+
+// utilities
+namespace detail {
+
+template<class CharT, class Traits = std::char_traits<CharT>>
+class save_istream
+{
+protected:
+    std::basic_ios<CharT, Traits>& is_;
+    CharT fill_;
+    std::ios::fmtflags flags_;
+    std::streamsize precision_;
+    std::streamsize width_;
+    std::basic_ostream<CharT, Traits>* tie_;
+    std::locale loc_;
+
+public:
+    ~save_istream()
+    {
+        is_.fill(fill_);
+        is_.flags(flags_);
+        is_.precision(precision_);
+        is_.width(width_);
+        is_.imbue(loc_);
+        is_.tie(tie_);
+    }
+
+    save_istream(const save_istream&) = delete;
+    save_istream& operator=(const save_istream&) = delete;
+
+    explicit save_istream(std::basic_ios<CharT, Traits>& is)
+        : is_(is)
+        , fill_(is.fill())
+        , flags_(is.flags())
+        , precision_(is.precision())
+        , width_(is.width(0))
+        , tie_(is.tie(nullptr))
+        , loc_(is.getloc())
+        {
+            if (tie_ != nullptr)
+                tie_->flush();
+        }
+};
+
+template<class CharT, class Traits = std::char_traits<CharT>>
+class save_ostream
+    : private save_istream<CharT, Traits>
+{
+public:
+    ~save_ostream()
+    {
+        if ((this->flags_ & std::ios::unitbuf) &&
+#if HAS_UNCAUGHT_EXCEPTIONS
+                std::uncaught_exceptions() == 0 &&
+#else
+                !std::uncaught_exception() &&
+#endif
+                this->is_.good())
+            this->is_.rdbuf()->pubsync();
+    }
+
+    save_ostream(const save_ostream&) = delete;
+    save_ostream& operator=(const save_ostream&) = delete;
+
+    explicit save_ostream(std::basic_ios<CharT, Traits>& os)
+        : save_istream<CharT, Traits>(os)
+        {
+        }
+};
+
+template <class T>
+struct choose_trunc_type
+{
+    static const int digits = std::numeric_limits<T>::digits;
+    using type = typename std::conditional
+                 <
+                     digits < 32,
+                     std::int32_t,
+                     typename std::conditional
+                     <
+                         digits < 64,
+                         std::int64_t,
+#ifdef __SIZEOF_INT128__
+                         __int128
+#else
+                         std::int64_t
+#endif
+                     >::type
+                 >::type;
+};
+
+template <class T>
+CONSTCD11
+inline
+typename std::enable_if
+<
+    !std::chrono::treat_as_floating_point<T>::value,
+    T
+>::type
+trunc(T t) NOEXCEPT
+{
+    return t;
+}
+
+template <class T>
+CONSTCD14
+inline
+typename std::enable_if
+<
+    std::chrono::treat_as_floating_point<T>::value,
+    T
+>::type
+trunc(T t) NOEXCEPT
+{
+    using std::numeric_limits;
+    using I = typename choose_trunc_type<T>::type;
+    CONSTDATA auto digits = numeric_limits<T>::digits;
+    static_assert(digits < numeric_limits<I>::digits, "");
+    CONSTDATA auto max = I{1} << (digits-1);
+    CONSTDATA auto min = -max;
+    const auto negative = t < T{0};
+    if (min <= t && t <= max && t != 0 && t == t)
+    {
+        t = static_cast<T>(static_cast<I>(t));
+        if (t == 0 && negative)
+            t = -t;
+    }
+    return t;
+}
+
+template <std::intmax_t Xp, std::intmax_t Yp>
+struct static_gcd
+{
+    static const std::intmax_t value = static_gcd<Yp, Xp % Yp>::value;
+};
+
+template <std::intmax_t Xp>
+struct static_gcd<Xp, 0>
+{
+    static const std::intmax_t value = Xp;
+};
+
+template <>
+struct static_gcd<0, 0>
+{
+    static const std::intmax_t value = 1;
+};
+
+template <class R1, class R2>
+struct no_overflow
+{
+private:
+    static const std::intmax_t gcd_n1_n2 = static_gcd<R1::num, R2::num>::value;
+    static const std::intmax_t gcd_d1_d2 = static_gcd<R1::den, R2::den>::value;
+    static const std::intmax_t n1 = R1::num / gcd_n1_n2;
+    static const std::intmax_t d1 = R1::den / gcd_d1_d2;
+    static const std::intmax_t n2 = R2::num / gcd_n1_n2;
+    static const std::intmax_t d2 = R2::den / gcd_d1_d2;
+#ifdef __cpp_constexpr
+    static const std::intmax_t max = std::numeric_limits<std::intmax_t>::max();
+#else
+    static const std::intmax_t max = LLONG_MAX;
+#endif
+
+    template <std::intmax_t Xp, std::intmax_t Yp, bool overflow>
+    struct mul    // overflow == false
+    {
+        static const std::intmax_t value = Xp * Yp;
+    };
+
+    template <std::intmax_t Xp, std::intmax_t Yp>
+    struct mul<Xp, Yp, true>
+    {
+        static const std::intmax_t value = 1;
+    };
+
+public:
+    static const bool value = (n1 <= max / d2) && (n2 <= max / d1);
+    typedef std::ratio<mul<n1, d2, !value>::value,
+                       mul<n2, d1, !value>::value> type;
+};
+
+}  // detail
+
+// trunc towards zero
+template <class To, class Rep, class Period>
+CONSTCD11
+inline
+typename std::enable_if
+<
+    detail::no_overflow<Period, typename To::period>::value,
+    To
+>::type
+trunc(const std::chrono::duration<Rep, Period>& d)
+{
+    return To{detail::trunc(std::chrono::duration_cast<To>(d).count())};
+}
+
+template <class To, class Rep, class Period>
+CONSTCD11
+inline
+typename std::enable_if
+<
+    !detail::no_overflow<Period, typename To::period>::value,
+    To
+>::type
+trunc(const std::chrono::duration<Rep, Period>& d)
+{
+    using std::chrono::duration_cast;
+    using std::chrono::duration;
+    using rep = typename std::common_type<Rep, typename To::rep>::type;
+    return To{detail::trunc(duration_cast<To>(duration_cast<duration<rep>>(d)).count())};
+}
+
+#ifndef HAS_CHRONO_ROUNDING
+#  if defined(_MSC_FULL_VER) && (_MSC_FULL_VER >= 190023918 || (_MSC_FULL_VER >= 190000000 && defined (__clang__)))
+#    define HAS_CHRONO_ROUNDING 1
+#  elif defined(__cpp_lib_chrono) && __cplusplus > 201402 && __cpp_lib_chrono >= 201510
+#    define HAS_CHRONO_ROUNDING 1
+#  elif defined(_LIBCPP_VERSION) && __cplusplus > 201402 && _LIBCPP_VERSION >= 3800
+#    define HAS_CHRONO_ROUNDING 1
+#  else
+#    define HAS_CHRONO_ROUNDING 0
+#  endif
+#endif  // HAS_CHRONO_ROUNDING
+
+#if HAS_CHRONO_ROUNDING == 0
+
+// round down
+template <class To, class Rep, class Period>
+CONSTCD14
+inline
+typename std::enable_if
+<
+    detail::no_overflow<Period, typename To::period>::value,
+    To
+>::type
+floor(const std::chrono::duration<Rep, Period>& d)
+{
+    auto t = trunc<To>(d);
+    if (t > d)
+        return t - To{1};
+    return t;
+}
+
+template <class To, class Rep, class Period>
+CONSTCD14
+inline
+typename std::enable_if
+<
+    !detail::no_overflow<Period, typename To::period>::value,
+    To
+>::type
+floor(const std::chrono::duration<Rep, Period>& d)
+{
+    using rep = typename std::common_type<Rep, typename To::rep>::type;
+    return floor<To>(floor<std::chrono::duration<rep>>(d));
+}
+
+// round to nearest, to even on tie
+template <class To, class Rep, class Period>
+CONSTCD14
+inline
+To
+round(const std::chrono::duration<Rep, Period>& d)
+{
+    auto t0 = floor<To>(d);
+    auto t1 = t0 + To{1};
+    if (t1 == To{0} && t0 < To{0})
+        t1 = -t1;
+    auto diff0 = d - t0;
+    auto diff1 = t1 - d;
+    if (diff0 == diff1)
+    {
+        if (t0 - trunc<To>(t0/2)*2 == To{0})
+            return t0;
+        return t1;
+    }
+    if (diff0 < diff1)
+        return t0;
+    return t1;
+}
+
+// round up
+template <class To, class Rep, class Period>
+CONSTCD14
+inline
+To
+ceil(const std::chrono::duration<Rep, Period>& d)
+{
+    auto t = trunc<To>(d);
+    if (t < d)
+        return t + To{1};
+    return t;
+}
+
+template <class Rep, class Period,
+          class = typename std::enable_if
+          <
+              std::numeric_limits<Rep>::is_signed
+          >::type>
+CONSTCD11
+std::chrono::duration<Rep, Period>
+abs(std::chrono::duration<Rep, Period> d)
+{
+    return d >= d.zero() ? d : -d;
+}
+
+// round down
+template <class To, class Clock, class FromDuration>
+CONSTCD11
+inline
+std::chrono::time_point<Clock, To>
+floor(const std::chrono::time_point<Clock, FromDuration>& tp)
+{
+    using std::chrono::time_point;
+    return time_point<Clock, To>{date::floor<To>(tp.time_since_epoch())};
+}
+
+// round to nearest, to even on tie
+template <class To, class Clock, class FromDuration>
+CONSTCD11
+inline
+std::chrono::time_point<Clock, To>
+round(const std::chrono::time_point<Clock, FromDuration>& tp)
+{
+    using std::chrono::time_point;
+    return time_point<Clock, To>{round<To>(tp.time_since_epoch())};
+}
+
+// round up
+template <class To, class Clock, class FromDuration>
+CONSTCD11
+inline
+std::chrono::time_point<Clock, To>
+ceil(const std::chrono::time_point<Clock, FromDuration>& tp)
+{
+    using std::chrono::time_point;
+    return time_point<Clock, To>{ceil<To>(tp.time_since_epoch())};
+}
+
+#else  // HAS_CHRONO_ROUNDING == 1
+
+using std::chrono::floor;
+using std::chrono::ceil;
+using std::chrono::round;
+using std::chrono::abs;
+
+#endif  // HAS_CHRONO_ROUNDING
+
+namespace detail
+{
+
+template <class To, class Rep, class Period>
+CONSTCD14
+inline
+typename std::enable_if
+<
+    !std::chrono::treat_as_floating_point<typename To::rep>::value,
+    To
+>::type
+round_i(const std::chrono::duration<Rep, Period>& d)
+{
+    return round<To>(d);
+}
+
+template <class To, class Rep, class Period>
+CONSTCD14
+inline
+typename std::enable_if
+<
+    std::chrono::treat_as_floating_point<typename To::rep>::value,
+    To
+>::type
+round_i(const std::chrono::duration<Rep, Period>& d)
+{
+    return d;
+}
+
+template <class To, class Clock, class FromDuration>
+CONSTCD11
+inline
+std::chrono::time_point<Clock, To>
+round_i(const std::chrono::time_point<Clock, FromDuration>& tp)
+{
+    using std::chrono::time_point;
+    return time_point<Clock, To>{round_i<To>(tp.time_since_epoch())};
+}
+
+}  // detail
+
+// trunc towards zero
+template <class To, class Clock, class FromDuration>
+CONSTCD11
+inline
+std::chrono::time_point<Clock, To>
+trunc(const std::chrono::time_point<Clock, FromDuration>& tp)
+{
+    using std::chrono::time_point;
+    return time_point<Clock, To>{trunc<To>(tp.time_since_epoch())};
+}
+
+// day
+
+CONSTCD11 inline day::day(unsigned d) NOEXCEPT : d_(static_cast<decltype(d_)>(d)) {}
+CONSTCD14 inline day& day::operator++() NOEXCEPT {++d_; return *this;}
+CONSTCD14 inline day day::operator++(int) NOEXCEPT {auto tmp(*this); ++(*this); return tmp;}
+CONSTCD14 inline day& day::operator--() NOEXCEPT {--d_; return *this;}
+CONSTCD14 inline day day::operator--(int) NOEXCEPT {auto tmp(*this); --(*this); return tmp;}
+CONSTCD14 inline day& day::operator+=(const days& d) NOEXCEPT {*this = *this + d; return *this;}
+CONSTCD14 inline day& day::operator-=(const days& d) NOEXCEPT {*this = *this - d; return *this;}
+CONSTCD11 inline day::operator unsigned() const NOEXCEPT {return d_;}
+CONSTCD11 inline bool day::ok() const NOEXCEPT {return 1 <= d_ && d_ <= 31;}
+
+CONSTCD11
+inline
+bool
+operator==(const day& x, const day& y) NOEXCEPT
+{
+    return static_cast<unsigned>(x) == static_cast<unsigned>(y);
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const day& x, const day& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+CONSTCD11
+inline
+bool
+operator<(const day& x, const day& y) NOEXCEPT
+{
+    return static_cast<unsigned>(x) < static_cast<unsigned>(y);
+}
+
+CONSTCD11
+inline
+bool
+operator>(const day& x, const day& y) NOEXCEPT
+{
+    return y < x;
+}
+
+CONSTCD11
+inline
+bool
+operator<=(const day& x, const day& y) NOEXCEPT
+{
+    return !(y < x);
+}
+
+CONSTCD11
+inline
+bool
+operator>=(const day& x, const day& y) NOEXCEPT
+{
+    return !(x < y);
+}
+
+CONSTCD11
+inline
+days
+operator-(const day& x, const day& y) NOEXCEPT
+{
+    return days{static_cast<days::rep>(static_cast<unsigned>(x)
+                                     - static_cast<unsigned>(y))};
+}
+
+CONSTCD11
+inline
+day
+operator+(const day& x, const days& y) NOEXCEPT
+{
+    return day{static_cast<unsigned>(x) + static_cast<unsigned>(y.count())};
+}
+
+CONSTCD11
+inline
+day
+operator+(const days& x, const day& y) NOEXCEPT
+{
+    return y + x;
+}
+
+CONSTCD11
+inline
+day
+operator-(const day& x, const days& y) NOEXCEPT
+{
+    return x + -y;
+}
+
+namespace detail
+{
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+low_level_fmt(std::basic_ostream<CharT, Traits>& os, const day& d)
+{
+    detail::save_ostream<CharT, Traits> _(os);
+    os.fill('0');
+    os.flags(std::ios::dec | std::ios::right);
+    os.width(2);
+    os << static_cast<unsigned>(d);
+    return os;
+}
+
+}  // namespace detail
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const day& d)
+{
+    detail::low_level_fmt(os, d);
+    if (!d.ok())
+        os << " is not a valid day";
+    return os;
+}
+
+// month
+
+CONSTCD11 inline month::month(unsigned m) NOEXCEPT : m_(static_cast<decltype(m_)>(m)) {}
+CONSTCD14 inline month& month::operator++() NOEXCEPT {*this += months{1}; return *this;}
+CONSTCD14 inline month month::operator++(int) NOEXCEPT {auto tmp(*this); ++(*this); return tmp;}
+CONSTCD14 inline month& month::operator--() NOEXCEPT {*this -= months{1}; return *this;}
+CONSTCD14 inline month month::operator--(int) NOEXCEPT {auto tmp(*this); --(*this); return tmp;}
+
+CONSTCD14
+inline
+month&
+month::operator+=(const months& m) NOEXCEPT
+{
+    *this = *this + m;
+    return *this;
+}
+
+CONSTCD14
+inline
+month&
+month::operator-=(const months& m) NOEXCEPT
+{
+    *this = *this - m;
+    return *this;
+}
+
+CONSTCD11 inline month::operator unsigned() const NOEXCEPT {return m_;}
+CONSTCD11 inline bool month::ok() const NOEXCEPT {return 1 <= m_ && m_ <= 12;}
+
+CONSTCD11
+inline
+bool
+operator==(const month& x, const month& y) NOEXCEPT
+{
+    return static_cast<unsigned>(x) == static_cast<unsigned>(y);
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const month& x, const month& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+CONSTCD11
+inline
+bool
+operator<(const month& x, const month& y) NOEXCEPT
+{
+    return static_cast<unsigned>(x) < static_cast<unsigned>(y);
+}
+
+CONSTCD11
+inline
+bool
+operator>(const month& x, const month& y) NOEXCEPT
+{
+    return y < x;
+}
+
+CONSTCD11
+inline
+bool
+operator<=(const month& x, const month& y) NOEXCEPT
+{
+    return !(y < x);
+}
+
+CONSTCD11
+inline
+bool
+operator>=(const month& x, const month& y) NOEXCEPT
+{
+    return !(x < y);
+}
+
+CONSTCD14
+inline
+months
+operator-(const month& x, const month& y) NOEXCEPT
+{
+    auto const d = static_cast<unsigned>(x) - static_cast<unsigned>(y);
+    return months(d <= 11 ? d : d + 12);
+}
+
+CONSTCD14
+inline
+month
+operator+(const month& x, const months& y) NOEXCEPT
+{
+    auto const mu = static_cast<long long>(static_cast<unsigned>(x)) + y.count() - 1;
+    auto const yr = (mu >= 0 ? mu : mu-11) / 12;
+    return month{static_cast<unsigned>(mu - yr * 12 + 1)};
+}
+
+CONSTCD14
+inline
+month
+operator+(const months& x, const month& y) NOEXCEPT
+{
+    return y + x;
+}
+
+CONSTCD14
+inline
+month
+operator-(const month& x, const months& y) NOEXCEPT
+{
+    return x + -y;
+}
+
+namespace detail
+{
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+low_level_fmt(std::basic_ostream<CharT, Traits>& os, const month& m)
+{
+    if (m.ok())
+    {
+        CharT fmt[] = {'%', 'b', 0};
+        os << format(os.getloc(), fmt, m);
+    }
+    else
+        os << static_cast<unsigned>(m);
+    return os;
+}
+
+}  // namespace detail
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const month& m)
+{
+    detail::low_level_fmt(os, m);
+    if (!m.ok())
+        os << " is not a valid month";
+    return os;
+}
+
+// year
+
+CONSTCD11 inline year::year(int y) NOEXCEPT : y_(static_cast<decltype(y_)>(y)) {}
+CONSTCD14 inline year& year::operator++() NOEXCEPT {++y_; return *this;}
+CONSTCD14 inline year year::operator++(int) NOEXCEPT {auto tmp(*this); ++(*this); return tmp;}
+CONSTCD14 inline year& year::operator--() NOEXCEPT {--y_; return *this;}
+CONSTCD14 inline year year::operator--(int) NOEXCEPT {auto tmp(*this); --(*this); return tmp;}
+CONSTCD14 inline year& year::operator+=(const years& y) NOEXCEPT {*this = *this + y; return *this;}
+CONSTCD14 inline year& year::operator-=(const years& y) NOEXCEPT {*this = *this - y; return *this;}
+CONSTCD11 inline year year::operator-() const NOEXCEPT {return year{-y_};}
+CONSTCD11 inline year year::operator+() const NOEXCEPT {return *this;}
+
+CONSTCD11
+inline
+bool
+year::is_leap() const NOEXCEPT
+{
+    return y_ % 4 == 0 && (y_ % 100 != 0 || y_ % 400 == 0);
+}
+
+CONSTCD11 inline year::operator int() const NOEXCEPT {return y_;}
+
+CONSTCD11
+inline
+bool
+year::ok() const NOEXCEPT
+{
+    return y_ != std::numeric_limits<short>::min();
+}
+
+CONSTCD11
+inline
+bool
+operator==(const year& x, const year& y) NOEXCEPT
+{
+    return static_cast<int>(x) == static_cast<int>(y);
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const year& x, const year& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+CONSTCD11
+inline
+bool
+operator<(const year& x, const year& y) NOEXCEPT
+{
+    return static_cast<int>(x) < static_cast<int>(y);
+}
+
+CONSTCD11
+inline
+bool
+operator>(const year& x, const year& y) NOEXCEPT
+{
+    return y < x;
+}
+
+CONSTCD11
+inline
+bool
+operator<=(const year& x, const year& y) NOEXCEPT
+{
+    return !(y < x);
+}
+
+CONSTCD11
+inline
+bool
+operator>=(const year& x, const year& y) NOEXCEPT
+{
+    return !(x < y);
+}
+
+CONSTCD11
+inline
+years
+operator-(const year& x, const year& y) NOEXCEPT
+{
+    return years{static_cast<int>(x) - static_cast<int>(y)};
+}
+
+CONSTCD11
+inline
+year
+operator+(const year& x, const years& y) NOEXCEPT
+{
+    return year{static_cast<int>(x) + y.count()};
+}
+
+CONSTCD11
+inline
+year
+operator+(const years& x, const year& y) NOEXCEPT
+{
+    return y + x;
+}
+
+CONSTCD11
+inline
+year
+operator-(const year& x, const years& y) NOEXCEPT
+{
+    return year{static_cast<int>(x) - y.count()};
+}
+
+namespace detail
+{
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+low_level_fmt(std::basic_ostream<CharT, Traits>& os, const year& y)
+{
+    detail::save_ostream<CharT, Traits> _(os);
+    os.fill('0');
+    os.flags(std::ios::dec | std::ios::internal);
+    os.width(4 + (y < year{0}));
+    os.imbue(std::locale::classic());
+    os << static_cast<int>(y);
+    return os;
+}
+
+}  // namespace detail
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year& y)
+{
+    detail::low_level_fmt(os, y);
+    if (!y.ok())
+        os << " is not a valid year";
+    return os;
+}
+
+// weekday
+
+CONSTCD14
+inline
+unsigned char
+weekday::weekday_from_days(int z) NOEXCEPT
+{
+    auto u = static_cast<unsigned>(z);
+    return static_cast<unsigned char>(z >= -4 ? (u+4) % 7 : u % 7);
+}
+
+CONSTCD11
+inline
+weekday::weekday(unsigned wd) NOEXCEPT
+    : wd_(static_cast<decltype(wd_)>(wd != 7 ? wd : 0))
+    {}
+
+CONSTCD14
+inline
+weekday::weekday(const sys_days& dp) NOEXCEPT
+    : wd_(weekday_from_days(dp.time_since_epoch().count()))
+    {}
+
+CONSTCD14
+inline
+weekday::weekday(const local_days& dp) NOEXCEPT
+    : wd_(weekday_from_days(dp.time_since_epoch().count()))
+    {}
+
+CONSTCD14 inline weekday& weekday::operator++() NOEXCEPT {*this += days{1}; return *this;}
+CONSTCD14 inline weekday weekday::operator++(int) NOEXCEPT {auto tmp(*this); ++(*this); return tmp;}
+CONSTCD14 inline weekday& weekday::operator--() NOEXCEPT {*this -= days{1}; return *this;}
+CONSTCD14 inline weekday weekday::operator--(int) NOEXCEPT {auto tmp(*this); --(*this); return tmp;}
+
+CONSTCD14
+inline
+weekday&
+weekday::operator+=(const days& d) NOEXCEPT
+{
+    *this = *this + d;
+    return *this;
+}
+
+CONSTCD14
+inline
+weekday&
+weekday::operator-=(const days& d) NOEXCEPT
+{
+    *this = *this - d;
+    return *this;
+}
+
+CONSTCD11 inline bool weekday::ok() const NOEXCEPT {return wd_ <= 6;}
+
+CONSTCD11
+inline
+unsigned weekday::c_encoding() const NOEXCEPT
+{
+    return unsigned{wd_};
+}
+
+CONSTCD11
+inline
+unsigned weekday::iso_encoding() const NOEXCEPT
+{
+    return unsigned{((wd_ == 0u) ? 7u : wd_)};
+}
+
+CONSTCD11
+inline
+bool
+operator==(const weekday& x, const weekday& y) NOEXCEPT
+{
+    return x.wd_ == y.wd_;
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const weekday& x, const weekday& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+CONSTCD14
+inline
+days
+operator-(const weekday& x, const weekday& y) NOEXCEPT
+{
+    auto const wdu = x.wd_ - y.wd_;
+    auto const wk = (wdu >= 0 ? wdu : wdu-6) / 7;
+    return days{wdu - wk * 7};
+}
+
+CONSTCD14
+inline
+weekday
+operator+(const weekday& x, const days& y) NOEXCEPT
+{
+    auto const wdu = static_cast<long long>(static_cast<unsigned>(x.wd_)) + y.count();
+    auto const wk = (wdu >= 0 ? wdu : wdu-6) / 7;
+    return weekday{static_cast<unsigned>(wdu - wk * 7)};
+}
+
+CONSTCD14
+inline
+weekday
+operator+(const days& x, const weekday& y) NOEXCEPT
+{
+    return y + x;
+}
+
+CONSTCD14
+inline
+weekday
+operator-(const weekday& x, const days& y) NOEXCEPT
+{
+    return x + -y;
+}
+
+namespace detail
+{
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+low_level_fmt(std::basic_ostream<CharT, Traits>& os, const weekday& wd)
+{
+    if (wd.ok())
+    {
+        CharT fmt[] = {'%', 'a', 0};
+        os << format(fmt, wd);
+    }
+    else
+        os << wd.c_encoding();
+    return os;
+}
+
+}  // namespace detail
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const weekday& wd)
+{
+    detail::low_level_fmt(os, wd);
+    if (!wd.ok())
+        os << " is not a valid weekday";
+    return os;
+}
+
+#if !defined(_MSC_VER) || (_MSC_VER >= 1900)
+inline namespace literals
+{
+
+CONSTCD11
+inline
+date::day
+operator "" _d(unsigned long long d) NOEXCEPT
+{
+    return date::day{static_cast<unsigned>(d)};
+}
+
+CONSTCD11
+inline
+date::year
+operator "" _y(unsigned long long y) NOEXCEPT
+{
+    return date::year(static_cast<int>(y));
+}
+#endif  // !defined(_MSC_VER) || (_MSC_VER >= 1900)
+
+CONSTDATA date::last_spec last{};
+
+CONSTDATA date::month jan{1};
+CONSTDATA date::month feb{2};
+CONSTDATA date::month mar{3};
+CONSTDATA date::month apr{4};
+CONSTDATA date::month may{5};
+CONSTDATA date::month jun{6};
+CONSTDATA date::month jul{7};
+CONSTDATA date::month aug{8};
+CONSTDATA date::month sep{9};
+CONSTDATA date::month oct{10};
+CONSTDATA date::month nov{11};
+CONSTDATA date::month dec{12};
+
+CONSTDATA date::weekday sun{0u};
+CONSTDATA date::weekday mon{1u};
+CONSTDATA date::weekday tue{2u};
+CONSTDATA date::weekday wed{3u};
+CONSTDATA date::weekday thu{4u};
+CONSTDATA date::weekday fri{5u};
+CONSTDATA date::weekday sat{6u};
+
+#if !defined(_MSC_VER) || (_MSC_VER >= 1900)
+}  // inline namespace literals
+#endif
+
+CONSTDATA date::month January{1};
+CONSTDATA date::month February{2};
+CONSTDATA date::month March{3};
+CONSTDATA date::month April{4};
+CONSTDATA date::month May{5};
+CONSTDATA date::month June{6};
+CONSTDATA date::month July{7};
+CONSTDATA date::month August{8};
+CONSTDATA date::month September{9};
+CONSTDATA date::month October{10};
+CONSTDATA date::month November{11};
+CONSTDATA date::month December{12};
+
+CONSTDATA date::weekday Monday{1};
+CONSTDATA date::weekday Tuesday{2};
+CONSTDATA date::weekday Wednesday{3};
+CONSTDATA date::weekday Thursday{4};
+CONSTDATA date::weekday Friday{5};
+CONSTDATA date::weekday Saturday{6};
+CONSTDATA date::weekday Sunday{7};
+
+// weekday_indexed
+
+CONSTCD11
+inline
+weekday
+weekday_indexed::weekday() const NOEXCEPT
+{
+    return date::weekday{static_cast<unsigned>(wd_)};
+}
+
+CONSTCD11 inline unsigned weekday_indexed::index() const NOEXCEPT {return index_;}
+
+CONSTCD11
+inline
+bool
+weekday_indexed::ok() const NOEXCEPT
+{
+    return weekday().ok() && 1 <= index_ && index_ <= 5;
+}
+
+#ifdef __GNUC__
+#  pragma GCC diagnostic push
+#  pragma GCC diagnostic ignored "-Wconversion"
+#endif  // __GNUC__
+
+CONSTCD11
+inline
+weekday_indexed::weekday_indexed(const date::weekday& wd, unsigned index) NOEXCEPT
+    : wd_(static_cast<decltype(wd_)>(static_cast<unsigned>(wd.wd_)))
+    , index_(static_cast<decltype(index_)>(index))
+    {}
+
+#ifdef __GNUC__
+#  pragma GCC diagnostic pop
+#endif  // __GNUC__
+
+namespace detail
+{
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+low_level_fmt(std::basic_ostream<CharT, Traits>& os, const weekday_indexed& wdi)
+{
+    return low_level_fmt(os, wdi.weekday()) << '[' << wdi.index() << ']';
+}
+
+}  // namespace detail
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const weekday_indexed& wdi)
+{
+    detail::low_level_fmt(os, wdi);
+    if (!wdi.ok())
+        os << " is not a valid weekday_indexed";
+    return os;
+}
+
+CONSTCD11
+inline
+weekday_indexed
+weekday::operator[](unsigned index) const NOEXCEPT
+{
+    return {*this, index};
+}
+
+CONSTCD11
+inline
+bool
+operator==(const weekday_indexed& x, const weekday_indexed& y) NOEXCEPT
+{
+    return x.weekday() == y.weekday() && x.index() == y.index();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const weekday_indexed& x, const weekday_indexed& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+// weekday_last
+
+CONSTCD11 inline date::weekday weekday_last::weekday() const NOEXCEPT {return wd_;}
+CONSTCD11 inline bool weekday_last::ok() const NOEXCEPT {return wd_.ok();}
+CONSTCD11 inline weekday_last::weekday_last(const date::weekday& wd) NOEXCEPT : wd_(wd) {}
+
+CONSTCD11
+inline
+bool
+operator==(const weekday_last& x, const weekday_last& y) NOEXCEPT
+{
+    return x.weekday() == y.weekday();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const weekday_last& x, const weekday_last& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+namespace detail
+{
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+low_level_fmt(std::basic_ostream<CharT, Traits>& os, const weekday_last& wdl)
+{
+    return low_level_fmt(os, wdl.weekday()) << "[last]";
+}
+
+}  // namespace detail
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const weekday_last& wdl)
+{
+    detail::low_level_fmt(os, wdl);
+    if (!wdl.ok())
+        os << " is not a valid weekday_last";
+    return os;
+}
+
+CONSTCD11
+inline
+weekday_last
+weekday::operator[](last_spec) const NOEXCEPT
+{
+    return weekday_last{*this};
+}
+
+// year_month
+
+CONSTCD11
+inline
+year_month::year_month(const date::year& y, const date::month& m) NOEXCEPT
+    : y_(y)
+    , m_(m)
+    {}
+
+CONSTCD11 inline year year_month::year() const NOEXCEPT {return y_;}
+CONSTCD11 inline month year_month::month() const NOEXCEPT {return m_;}
+CONSTCD11 inline bool year_month::ok() const NOEXCEPT {return y_.ok() && m_.ok();}
+
+template<class>
+CONSTCD14
+inline
+year_month&
+year_month::operator+=(const months& dm) NOEXCEPT
+{
+    *this = *this + dm;
+    return *this;
+}
+
+template<class>
+CONSTCD14
+inline
+year_month&
+year_month::operator-=(const months& dm) NOEXCEPT
+{
+    *this = *this - dm;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month&
+year_month::operator+=(const years& dy) NOEXCEPT
+{
+    *this = *this + dy;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month&
+year_month::operator-=(const years& dy) NOEXCEPT
+{
+    *this = *this - dy;
+    return *this;
+}
+
+CONSTCD11
+inline
+bool
+operator==(const year_month& x, const year_month& y) NOEXCEPT
+{
+    return x.year() == y.year() && x.month() == y.month();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const year_month& x, const year_month& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+CONSTCD11
+inline
+bool
+operator<(const year_month& x, const year_month& y) NOEXCEPT
+{
+    return x.year() < y.year() ? true
+        : (x.year() > y.year() ? false
+        : (x.month() < y.month()));
+}
+
+CONSTCD11
+inline
+bool
+operator>(const year_month& x, const year_month& y) NOEXCEPT
+{
+    return y < x;
+}
+
+CONSTCD11
+inline
+bool
+operator<=(const year_month& x, const year_month& y) NOEXCEPT
+{
+    return !(y < x);
+}
+
+CONSTCD11
+inline
+bool
+operator>=(const year_month& x, const year_month& y) NOEXCEPT
+{
+    return !(x < y);
+}
+
+template<class>
+CONSTCD14
+inline
+year_month
+operator+(const year_month& ym, const months& dm) NOEXCEPT
+{
+    auto dmi = static_cast<int>(static_cast<unsigned>(ym.month())) - 1 + dm.count();
+    auto dy = (dmi >= 0 ? dmi : dmi-11) / 12;
+    dmi = dmi - dy * 12 + 1;
+    return (ym.year() + years(dy)) / month(static_cast<unsigned>(dmi));
+}
+
+template<class>
+CONSTCD14
+inline
+year_month
+operator+(const months& dm, const year_month& ym) NOEXCEPT
+{
+    return ym + dm;
+}
+
+template<class>
+CONSTCD14
+inline
+year_month
+operator-(const year_month& ym, const months& dm) NOEXCEPT
+{
+    return ym + -dm;
+}
+
+CONSTCD11
+inline
+months
+operator-(const year_month& x, const year_month& y) NOEXCEPT
+{
+    return (x.year() - y.year()) +
+            months(static_cast<unsigned>(x.month()) - static_cast<unsigned>(y.month()));
+}
+
+CONSTCD11
+inline
+year_month
+operator+(const year_month& ym, const years& dy) NOEXCEPT
+{
+    return (ym.year() + dy) / ym.month();
+}
+
+CONSTCD11
+inline
+year_month
+operator+(const years& dy, const year_month& ym) NOEXCEPT
+{
+    return ym + dy;
+}
+
+CONSTCD11
+inline
+year_month
+operator-(const year_month& ym, const years& dy) NOEXCEPT
+{
+    return ym + -dy;
+}
+
+namespace detail
+{
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+low_level_fmt(std::basic_ostream<CharT, Traits>& os, const year_month& ym)
+{
+    low_level_fmt(os, ym.year()) << '/';
+    return low_level_fmt(os, ym.month());
+}
+
+}  // namespace detail
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_month& ym)
+{
+    detail::low_level_fmt(os, ym);
+    if (!ym.ok())
+        os << " is not a valid year_month";
+    return os;
+}
+
+// month_day
+
+CONSTCD11
+inline
+month_day::month_day(const date::month& m, const date::day& d) NOEXCEPT
+    : m_(m)
+    , d_(d)
+    {}
+
+CONSTCD11 inline date::month month_day::month() const NOEXCEPT {return m_;}
+CONSTCD11 inline date::day month_day::day() const NOEXCEPT {return d_;}
+
+CONSTCD14
+inline
+bool
+month_day::ok() const NOEXCEPT
+{
+    CONSTDATA date::day d[] =
+    {
+        date::day(31), date::day(29), date::day(31),
+        date::day(30), date::day(31), date::day(30),
+        date::day(31), date::day(31), date::day(30),
+        date::day(31), date::day(30), date::day(31)
+    };
+    return m_.ok() && date::day{1} <= d_ && d_ <= d[static_cast<unsigned>(m_)-1];
+}
+
+CONSTCD11
+inline
+bool
+operator==(const month_day& x, const month_day& y) NOEXCEPT
+{
+    return x.month() == y.month() && x.day() == y.day();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const month_day& x, const month_day& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+CONSTCD11
+inline
+bool
+operator<(const month_day& x, const month_day& y) NOEXCEPT
+{
+    return x.month() < y.month() ? true
+        : (x.month() > y.month() ? false
+        : (x.day() < y.day()));
+}
+
+CONSTCD11
+inline
+bool
+operator>(const month_day& x, const month_day& y) NOEXCEPT
+{
+    return y < x;
+}
+
+CONSTCD11
+inline
+bool
+operator<=(const month_day& x, const month_day& y) NOEXCEPT
+{
+    return !(y < x);
+}
+
+CONSTCD11
+inline
+bool
+operator>=(const month_day& x, const month_day& y) NOEXCEPT
+{
+    return !(x < y);
+}
+
+namespace detail
+{
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+low_level_fmt(std::basic_ostream<CharT, Traits>& os, const month_day& md)
+{
+    low_level_fmt(os, md.month()) << '/';
+    return low_level_fmt(os, md.day());
+}
+
+}  // namespace detail
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const month_day& md)
+{
+    detail::low_level_fmt(os, md);
+    if (!md.ok())
+        os << " is not a valid month_day";
+    return os;
+}
+
+// month_day_last
+
+CONSTCD11 inline month month_day_last::month() const NOEXCEPT {return m_;}
+CONSTCD11 inline bool month_day_last::ok() const NOEXCEPT {return m_.ok();}
+CONSTCD11 inline month_day_last::month_day_last(const date::month& m) NOEXCEPT : m_(m) {}
+
+CONSTCD11
+inline
+bool
+operator==(const month_day_last& x, const month_day_last& y) NOEXCEPT
+{
+    return x.month() == y.month();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const month_day_last& x, const month_day_last& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+CONSTCD11
+inline
+bool
+operator<(const month_day_last& x, const month_day_last& y) NOEXCEPT
+{
+    return x.month() < y.month();
+}
+
+CONSTCD11
+inline
+bool
+operator>(const month_day_last& x, const month_day_last& y) NOEXCEPT
+{
+    return y < x;
+}
+
+CONSTCD11
+inline
+bool
+operator<=(const month_day_last& x, const month_day_last& y) NOEXCEPT
+{
+    return !(y < x);
+}
+
+CONSTCD11
+inline
+bool
+operator>=(const month_day_last& x, const month_day_last& y) NOEXCEPT
+{
+    return !(x < y);
+}
+
+namespace detail
+{
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+low_level_fmt(std::basic_ostream<CharT, Traits>& os, const month_day_last& mdl)
+{
+    return low_level_fmt(os, mdl.month()) << "/last";
+}
+
+}  // namespace detail
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const month_day_last& mdl)
+{
+    detail::low_level_fmt(os, mdl);
+    if (!mdl.ok())
+        os << " is not a valid month_day_last";
+    return os;
+}
+
+// month_weekday
+
+CONSTCD11
+inline
+month_weekday::month_weekday(const date::month& m,
+                             const date::weekday_indexed& wdi) NOEXCEPT
+    : m_(m)
+    , wdi_(wdi)
+    {}
+
+CONSTCD11 inline month month_weekday::month() const NOEXCEPT {return m_;}
+
+CONSTCD11
+inline
+weekday_indexed
+month_weekday::weekday_indexed() const NOEXCEPT
+{
+    return wdi_;
+}
+
+CONSTCD11
+inline
+bool
+month_weekday::ok() const NOEXCEPT
+{
+    return m_.ok() && wdi_.ok();
+}
+
+CONSTCD11
+inline
+bool
+operator==(const month_weekday& x, const month_weekday& y) NOEXCEPT
+{
+    return x.month() == y.month() && x.weekday_indexed() == y.weekday_indexed();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const month_weekday& x, const month_weekday& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+namespace detail
+{
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+low_level_fmt(std::basic_ostream<CharT, Traits>& os, const month_weekday& mwd)
+{
+    low_level_fmt(os, mwd.month()) << '/';
+    return low_level_fmt(os, mwd.weekday_indexed());
+}
+
+}  // namespace detail
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const month_weekday& mwd)
+{
+    detail::low_level_fmt(os, mwd);
+    if (!mwd.ok())
+        os << " is not a valid month_weekday";
+    return os;
+}
+
+// month_weekday_last
+
+CONSTCD11
+inline
+month_weekday_last::month_weekday_last(const date::month& m,
+                                       const date::weekday_last& wdl) NOEXCEPT
+    : m_(m)
+    , wdl_(wdl)
+    {}
+
+CONSTCD11 inline month month_weekday_last::month() const NOEXCEPT {return m_;}
+
+CONSTCD11
+inline
+weekday_last
+month_weekday_last::weekday_last() const NOEXCEPT
+{
+    return wdl_;
+}
+
+CONSTCD11
+inline
+bool
+month_weekday_last::ok() const NOEXCEPT
+{
+    return m_.ok() && wdl_.ok();
+}
+
+CONSTCD11
+inline
+bool
+operator==(const month_weekday_last& x, const month_weekday_last& y) NOEXCEPT
+{
+    return x.month() == y.month() && x.weekday_last() == y.weekday_last();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const month_weekday_last& x, const month_weekday_last& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+namespace detail
+{
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+low_level_fmt(std::basic_ostream<CharT, Traits>& os, const month_weekday_last& mwdl)
+{
+    low_level_fmt(os, mwdl.month()) << '/';
+    return low_level_fmt(os, mwdl.weekday_last());
+}
+
+}  // namespace detail
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const month_weekday_last& mwdl)
+{
+    detail::low_level_fmt(os, mwdl);
+    if (!mwdl.ok())
+        os << " is not a valid month_weekday_last";
+    return os;
+}
+
+// year_month_day_last
+
+CONSTCD11
+inline
+year_month_day_last::year_month_day_last(const date::year& y,
+                                         const date::month_day_last& mdl) NOEXCEPT
+    : y_(y)
+    , mdl_(mdl)
+    {}
+
+template<class>
+CONSTCD14
+inline
+year_month_day_last&
+year_month_day_last::operator+=(const months& m) NOEXCEPT
+{
+    *this = *this + m;
+    return *this;
+}
+
+template<class>
+CONSTCD14
+inline
+year_month_day_last&
+year_month_day_last::operator-=(const months& m) NOEXCEPT
+{
+    *this = *this - m;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month_day_last&
+year_month_day_last::operator+=(const years& y) NOEXCEPT
+{
+    *this = *this + y;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month_day_last&
+year_month_day_last::operator-=(const years& y) NOEXCEPT
+{
+    *this = *this - y;
+    return *this;
+}
+
+CONSTCD11 inline year year_month_day_last::year() const NOEXCEPT {return y_;}
+CONSTCD11 inline month year_month_day_last::month() const NOEXCEPT {return mdl_.month();}
+
+CONSTCD11
+inline
+month_day_last
+year_month_day_last::month_day_last() const NOEXCEPT
+{
+    return mdl_;
+}
+
+CONSTCD14
+inline
+day
+year_month_day_last::day() const NOEXCEPT
+{
+    CONSTDATA date::day d[] =
+    {
+        date::day(31), date::day(28), date::day(31),
+        date::day(30), date::day(31), date::day(30),
+        date::day(31), date::day(31), date::day(30),
+        date::day(31), date::day(30), date::day(31)
+    };
+    return (month() != February || !y_.is_leap()) && mdl_.ok() ?
+        d[static_cast<unsigned>(month()) - 1] : date::day{29};
+}
+
+CONSTCD14
+inline
+year_month_day_last::operator sys_days() const NOEXCEPT
+{
+    return sys_days(year()/month()/day());
+}
+
+CONSTCD14
+inline
+year_month_day_last::operator local_days() const NOEXCEPT
+{
+    return local_days(year()/month()/day());
+}
+
+CONSTCD11
+inline
+bool
+year_month_day_last::ok() const NOEXCEPT
+{
+    return y_.ok() && mdl_.ok();
+}
+
+CONSTCD11
+inline
+bool
+operator==(const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT
+{
+    return x.year() == y.year() && x.month_day_last() == y.month_day_last();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+CONSTCD11
+inline
+bool
+operator<(const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT
+{
+    return x.year() < y.year() ? true
+        : (x.year() > y.year() ? false
+        : (x.month_day_last() < y.month_day_last()));
+}
+
+CONSTCD11
+inline
+bool
+operator>(const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT
+{
+    return y < x;
+}
+
+CONSTCD11
+inline
+bool
+operator<=(const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT
+{
+    return !(y < x);
+}
+
+CONSTCD11
+inline
+bool
+operator>=(const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT
+{
+    return !(x < y);
+}
+
+namespace detail
+{
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+low_level_fmt(std::basic_ostream<CharT, Traits>& os, const year_month_day_last& ymdl)
+{
+    low_level_fmt(os, ymdl.year()) << '/';
+    return low_level_fmt(os, ymdl.month_day_last());
+}
+
+}  // namespace detail
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_month_day_last& ymdl)
+{
+    detail::low_level_fmt(os, ymdl);
+    if (!ymdl.ok())
+        os << " is not a valid year_month_day_last";
+    return os;
+}
+
+template<class>
+CONSTCD14
+inline
+year_month_day_last
+operator+(const year_month_day_last& ymdl, const months& dm) NOEXCEPT
+{
+    return (ymdl.year() / ymdl.month() + dm) / last;
+}
+
+template<class>
+CONSTCD14
+inline
+year_month_day_last
+operator+(const months& dm, const year_month_day_last& ymdl) NOEXCEPT
+{
+    return ymdl + dm;
+}
+
+template<class>
+CONSTCD14
+inline
+year_month_day_last
+operator-(const year_month_day_last& ymdl, const months& dm) NOEXCEPT
+{
+    return ymdl + (-dm);
+}
+
+CONSTCD11
+inline
+year_month_day_last
+operator+(const year_month_day_last& ymdl, const years& dy) NOEXCEPT
+{
+    return {ymdl.year()+dy, ymdl.month_day_last()};
+}
+
+CONSTCD11
+inline
+year_month_day_last
+operator+(const years& dy, const year_month_day_last& ymdl) NOEXCEPT
+{
+    return ymdl + dy;
+}
+
+CONSTCD11
+inline
+year_month_day_last
+operator-(const year_month_day_last& ymdl, const years& dy) NOEXCEPT
+{
+    return ymdl + (-dy);
+}
+
+// year_month_day
+
+CONSTCD11
+inline
+year_month_day::year_month_day(const date::year& y, const date::month& m,
+                               const date::day& d) NOEXCEPT
+    : y_(y)
+    , m_(m)
+    , d_(d)
+    {}
+
+CONSTCD14
+inline
+year_month_day::year_month_day(const year_month_day_last& ymdl) NOEXCEPT
+    : y_(ymdl.year())
+    , m_(ymdl.month())
+    , d_(ymdl.day())
+    {}
+
+CONSTCD14
+inline
+year_month_day::year_month_day(sys_days dp) NOEXCEPT
+    : year_month_day(from_days(dp.time_since_epoch()))
+    {}
+
+CONSTCD14
+inline
+year_month_day::year_month_day(local_days dp) NOEXCEPT
+    : year_month_day(from_days(dp.time_since_epoch()))
+    {}
+
+CONSTCD11 inline year year_month_day::year() const NOEXCEPT {return y_;}
+CONSTCD11 inline month year_month_day::month() const NOEXCEPT {return m_;}
+CONSTCD11 inline day year_month_day::day() const NOEXCEPT {return d_;}
+
+template<class>
+CONSTCD14
+inline
+year_month_day&
+year_month_day::operator+=(const months& m) NOEXCEPT
+{
+    *this = *this + m;
+    return *this;
+}
+
+template<class>
+CONSTCD14
+inline
+year_month_day&
+year_month_day::operator-=(const months& m) NOEXCEPT
+{
+    *this = *this - m;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month_day&
+year_month_day::operator+=(const years& y) NOEXCEPT
+{
+    *this = *this + y;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month_day&
+year_month_day::operator-=(const years& y) NOEXCEPT
+{
+    *this = *this - y;
+    return *this;
+}
+
+CONSTCD14
+inline
+days
+year_month_day::to_days() const NOEXCEPT
+{
+    static_assert(std::numeric_limits<unsigned>::digits >= 18,
+             "This algorithm has not been ported to a 16 bit unsigned integer");
+    static_assert(std::numeric_limits<int>::digits >= 20,
+             "This algorithm has not been ported to a 16 bit signed integer");
+    auto const y = static_cast<int>(y_) - (m_ <= February);
+    auto const m = static_cast<unsigned>(m_);
+    auto const d = static_cast<unsigned>(d_);
+    auto const era = (y >= 0 ? y : y-399) / 400;
+    auto const yoe = static_cast<unsigned>(y - era * 400);       // [0, 399]
+    auto const doy = (153*(m > 2 ? m-3 : m+9) + 2)/5 + d-1;      // [0, 365]
+    auto const doe = yoe * 365 + yoe/4 - yoe/100 + doy;          // [0, 146096]
+    return days{era * 146097 + static_cast<int>(doe) - 719468};
+}
+
+CONSTCD14
+inline
+year_month_day::operator sys_days() const NOEXCEPT
+{
+    return sys_days{to_days()};
+}
+
+CONSTCD14
+inline
+year_month_day::operator local_days() const NOEXCEPT
+{
+    return local_days{to_days()};
+}
+
+CONSTCD14
+inline
+bool
+year_month_day::ok() const NOEXCEPT
+{
+    if (!(y_.ok() && m_.ok()))
+        return false;
+    return date::day{1} <= d_ && d_ <= (y_ / m_ / last).day();
+}
+
+CONSTCD11
+inline
+bool
+operator==(const year_month_day& x, const year_month_day& y) NOEXCEPT
+{
+    return x.year() == y.year() && x.month() == y.month() && x.day() == y.day();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const year_month_day& x, const year_month_day& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+CONSTCD11
+inline
+bool
+operator<(const year_month_day& x, const year_month_day& y) NOEXCEPT
+{
+    return x.year() < y.year() ? true
+        : (x.year() > y.year() ? false
+        : (x.month() < y.month() ? true
+        : (x.month() > y.month() ? false
+        : (x.day() < y.day()))));
+}
+
+CONSTCD11
+inline
+bool
+operator>(const year_month_day& x, const year_month_day& y) NOEXCEPT
+{
+    return y < x;
+}
+
+CONSTCD11
+inline
+bool
+operator<=(const year_month_day& x, const year_month_day& y) NOEXCEPT
+{
+    return !(y < x);
+}
+
+CONSTCD11
+inline
+bool
+operator>=(const year_month_day& x, const year_month_day& y) NOEXCEPT
+{
+    return !(x < y);
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_month_day& ymd)
+{
+    detail::save_ostream<CharT, Traits> _(os);
+    os.fill('0');
+    os.flags(std::ios::dec | std::ios::right);
+    os.imbue(std::locale::classic());
+    os << static_cast<int>(ymd.year()) << '-';
+    os.width(2);
+    os << static_cast<unsigned>(ymd.month()) << '-';
+    os.width(2);
+    os << static_cast<unsigned>(ymd.day());
+    if (!ymd.ok())
+        os << " is not a valid year_month_day";
+    return os;
+}
+
+CONSTCD14
+inline
+year_month_day
+year_month_day::from_days(days dp) NOEXCEPT
+{
+    static_assert(std::numeric_limits<unsigned>::digits >= 18,
+             "This algorithm has not been ported to a 16 bit unsigned integer");
+    static_assert(std::numeric_limits<int>::digits >= 20,
+             "This algorithm has not been ported to a 16 bit signed integer");
+    auto const z = dp.count() + 719468;
+    auto const era = (z >= 0 ? z : z - 146096) / 146097;
+    auto const doe = static_cast<unsigned>(z - era * 146097);          // [0, 146096]
+    auto const yoe = (doe - doe/1460 + doe/36524 - doe/146096) / 365;  // [0, 399]
+    auto const y = static_cast<days::rep>(yoe) + era * 400;
+    auto const doy = doe - (365*yoe + yoe/4 - yoe/100);                // [0, 365]
+    auto const mp = (5*doy + 2)/153;                                   // [0, 11]
+    auto const d = doy - (153*mp+2)/5 + 1;                             // [1, 31]
+    auto const m = mp < 10 ? mp+3 : mp-9;                              // [1, 12]
+    return year_month_day{date::year{y + (m <= 2)}, date::month(m), date::day(d)};
+}
+
+template<class>
+CONSTCD14
+inline
+year_month_day
+operator+(const year_month_day& ymd, const months& dm) NOEXCEPT
+{
+    return (ymd.year() / ymd.month() + dm) / ymd.day();
+}
+
+template<class>
+CONSTCD14
+inline
+year_month_day
+operator+(const months& dm, const year_month_day& ymd) NOEXCEPT
+{
+    return ymd + dm;
+}
+
+template<class>
+CONSTCD14
+inline
+year_month_day
+operator-(const year_month_day& ymd, const months& dm) NOEXCEPT
+{
+    return ymd + (-dm);
+}
+
+CONSTCD11
+inline
+year_month_day
+operator+(const year_month_day& ymd, const years& dy) NOEXCEPT
+{
+    return (ymd.year() + dy) / ymd.month() / ymd.day();
+}
+
+CONSTCD11
+inline
+year_month_day
+operator+(const years& dy, const year_month_day& ymd) NOEXCEPT
+{
+    return ymd + dy;
+}
+
+CONSTCD11
+inline
+year_month_day
+operator-(const year_month_day& ymd, const years& dy) NOEXCEPT
+{
+    return ymd + (-dy);
+}
+
+// year_month_weekday
+
+CONSTCD11
+inline
+year_month_weekday::year_month_weekday(const date::year& y, const date::month& m,
+                                       const date::weekday_indexed& wdi)
+        NOEXCEPT
+    : y_(y)
+    , m_(m)
+    , wdi_(wdi)
+    {}
+
+CONSTCD14
+inline
+year_month_weekday::year_month_weekday(const sys_days& dp) NOEXCEPT
+    : year_month_weekday(from_days(dp.time_since_epoch()))
+    {}
+
+CONSTCD14
+inline
+year_month_weekday::year_month_weekday(const local_days& dp) NOEXCEPT
+    : year_month_weekday(from_days(dp.time_since_epoch()))
+    {}
+
+template<class>
+CONSTCD14
+inline
+year_month_weekday&
+year_month_weekday::operator+=(const months& m) NOEXCEPT
+{
+    *this = *this + m;
+    return *this;
+}
+
+template<class>
+CONSTCD14
+inline
+year_month_weekday&
+year_month_weekday::operator-=(const months& m) NOEXCEPT
+{
+    *this = *this - m;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month_weekday&
+year_month_weekday::operator+=(const years& y) NOEXCEPT
+{
+    *this = *this + y;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month_weekday&
+year_month_weekday::operator-=(const years& y) NOEXCEPT
+{
+    *this = *this - y;
+    return *this;
+}
+
+CONSTCD11 inline year year_month_weekday::year() const NOEXCEPT {return y_;}
+CONSTCD11 inline month year_month_weekday::month() const NOEXCEPT {return m_;}
+
+CONSTCD11
+inline
+weekday
+year_month_weekday::weekday() const NOEXCEPT
+{
+    return wdi_.weekday();
+}
+
+CONSTCD11
+inline
+unsigned
+year_month_weekday::index() const NOEXCEPT
+{
+    return wdi_.index();
+}
+
+CONSTCD11
+inline
+weekday_indexed
+year_month_weekday::weekday_indexed() const NOEXCEPT
+{
+    return wdi_;
+}
+
+CONSTCD14
+inline
+year_month_weekday::operator sys_days() const NOEXCEPT
+{
+    return sys_days{to_days()};
+}
+
+CONSTCD14
+inline
+year_month_weekday::operator local_days() const NOEXCEPT
+{
+    return local_days{to_days()};
+}
+
+CONSTCD14
+inline
+bool
+year_month_weekday::ok() const NOEXCEPT
+{
+    if (!y_.ok() || !m_.ok() || !wdi_.weekday().ok() || wdi_.index() < 1)
+        return false;
+    if (wdi_.index() <= 4)
+        return true;
+    auto d2 = wdi_.weekday() - date::weekday(static_cast<sys_days>(y_/m_/1)) +
+                  days((wdi_.index()-1)*7 + 1);
+    return static_cast<unsigned>(d2.count()) <= static_cast<unsigned>((y_/m_/last).day());
+}
+
+CONSTCD14
+inline
+year_month_weekday
+year_month_weekday::from_days(days d) NOEXCEPT
+{
+    sys_days dp{d};
+    auto const wd = date::weekday(dp);
+    auto const ymd = year_month_day(dp);
+    return {ymd.year(), ymd.month(), wd[(static_cast<unsigned>(ymd.day())-1)/7+1]};
+}
+
+CONSTCD14
+inline
+days
+year_month_weekday::to_days() const NOEXCEPT
+{
+    auto d = sys_days(y_/m_/1);
+    return (d + (wdi_.weekday() - date::weekday(d) + days{(wdi_.index()-1)*7})
+           ).time_since_epoch();
+}
+
+CONSTCD11
+inline
+bool
+operator==(const year_month_weekday& x, const year_month_weekday& y) NOEXCEPT
+{
+    return x.year() == y.year() && x.month() == y.month() &&
+           x.weekday_indexed() == y.weekday_indexed();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const year_month_weekday& x, const year_month_weekday& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_month_weekday& ymwdi)
+{
+    detail::low_level_fmt(os, ymwdi.year()) << '/';
+    detail::low_level_fmt(os, ymwdi.month()) << '/';
+    detail::low_level_fmt(os, ymwdi.weekday_indexed());
+    if (!ymwdi.ok())
+        os << " is not a valid year_month_weekday";
+    return os;
+}
+
+template<class>
+CONSTCD14
+inline
+year_month_weekday
+operator+(const year_month_weekday& ymwd, const months& dm) NOEXCEPT
+{
+    return (ymwd.year() / ymwd.month() + dm) / ymwd.weekday_indexed();
+}
+
+template<class>
+CONSTCD14
+inline
+year_month_weekday
+operator+(const months& dm, const year_month_weekday& ymwd) NOEXCEPT
+{
+    return ymwd + dm;
+}
+
+template<class>
+CONSTCD14
+inline
+year_month_weekday
+operator-(const year_month_weekday& ymwd, const months& dm) NOEXCEPT
+{
+    return ymwd + (-dm);
+}
+
+CONSTCD11
+inline
+year_month_weekday
+operator+(const year_month_weekday& ymwd, const years& dy) NOEXCEPT
+{
+    return {ymwd.year()+dy, ymwd.month(), ymwd.weekday_indexed()};
+}
+
+CONSTCD11
+inline
+year_month_weekday
+operator+(const years& dy, const year_month_weekday& ymwd) NOEXCEPT
+{
+    return ymwd + dy;
+}
+
+CONSTCD11
+inline
+year_month_weekday
+operator-(const year_month_weekday& ymwd, const years& dy) NOEXCEPT
+{
+    return ymwd + (-dy);
+}
+
+// year_month_weekday_last
+
+CONSTCD11
+inline
+year_month_weekday_last::year_month_weekday_last(const date::year& y,
+                                                 const date::month& m,
+                                                 const date::weekday_last& wdl) NOEXCEPT
+    : y_(y)
+    , m_(m)
+    , wdl_(wdl)
+    {}
+
+template<class>
+CONSTCD14
+inline
+year_month_weekday_last&
+year_month_weekday_last::operator+=(const months& m) NOEXCEPT
+{
+    *this = *this + m;
+    return *this;
+}
+
+template<class>
+CONSTCD14
+inline
+year_month_weekday_last&
+year_month_weekday_last::operator-=(const months& m) NOEXCEPT
+{
+    *this = *this - m;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month_weekday_last&
+year_month_weekday_last::operator+=(const years& y) NOEXCEPT
+{
+    *this = *this + y;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month_weekday_last&
+year_month_weekday_last::operator-=(const years& y) NOEXCEPT
+{
+    *this = *this - y;
+    return *this;
+}
+
+CONSTCD11 inline year year_month_weekday_last::year() const NOEXCEPT {return y_;}
+CONSTCD11 inline month year_month_weekday_last::month() const NOEXCEPT {return m_;}
+
+CONSTCD11
+inline
+weekday
+year_month_weekday_last::weekday() const NOEXCEPT
+{
+    return wdl_.weekday();
+}
+
+CONSTCD11
+inline
+weekday_last
+year_month_weekday_last::weekday_last() const NOEXCEPT
+{
+    return wdl_;
+}
+
+CONSTCD14
+inline
+year_month_weekday_last::operator sys_days() const NOEXCEPT
+{
+    return sys_days{to_days()};
+}
+
+CONSTCD14
+inline
+year_month_weekday_last::operator local_days() const NOEXCEPT
+{
+    return local_days{to_days()};
+}
+
+CONSTCD11
+inline
+bool
+year_month_weekday_last::ok() const NOEXCEPT
+{
+    return y_.ok() && m_.ok() && wdl_.ok();
+}
+
+CONSTCD14
+inline
+days
+year_month_weekday_last::to_days() const NOEXCEPT
+{
+    auto const d = sys_days(y_/m_/last);
+    return (d - (date::weekday{d} - wdl_.weekday())).time_since_epoch();
+}
+
+CONSTCD11
+inline
+bool
+operator==(const year_month_weekday_last& x, const year_month_weekday_last& y) NOEXCEPT
+{
+    return x.year() == y.year() && x.month() == y.month() &&
+           x.weekday_last() == y.weekday_last();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const year_month_weekday_last& x, const year_month_weekday_last& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_month_weekday_last& ymwdl)
+{
+    detail::low_level_fmt(os, ymwdl.year()) << '/';
+    detail::low_level_fmt(os, ymwdl.month()) << '/';
+    detail::low_level_fmt(os, ymwdl.weekday_last());
+    if (!ymwdl.ok())
+        os << " is not a valid year_month_weekday_last";
+    return os;
+}
+
+template<class>
+CONSTCD14
+inline
+year_month_weekday_last
+operator+(const year_month_weekday_last& ymwdl, const months& dm) NOEXCEPT
+{
+    return (ymwdl.year() / ymwdl.month() + dm) / ymwdl.weekday_last();
+}
+
+template<class>
+CONSTCD14
+inline
+year_month_weekday_last
+operator+(const months& dm, const year_month_weekday_last& ymwdl) NOEXCEPT
+{
+    return ymwdl + dm;
+}
+
+template<class>
+CONSTCD14
+inline
+year_month_weekday_last
+operator-(const year_month_weekday_last& ymwdl, const months& dm) NOEXCEPT
+{
+    return ymwdl + (-dm);
+}
+
+CONSTCD11
+inline
+year_month_weekday_last
+operator+(const year_month_weekday_last& ymwdl, const years& dy) NOEXCEPT
+{
+    return {ymwdl.year()+dy, ymwdl.month(), ymwdl.weekday_last()};
+}
+
+CONSTCD11
+inline
+year_month_weekday_last
+operator+(const years& dy, const year_month_weekday_last& ymwdl) NOEXCEPT
+{
+    return ymwdl + dy;
+}
+
+CONSTCD11
+inline
+year_month_weekday_last
+operator-(const year_month_weekday_last& ymwdl, const years& dy) NOEXCEPT
+{
+    return ymwdl + (-dy);
+}
+
+// year_month from operator/()
+
+CONSTCD11
+inline
+year_month
+operator/(const year& y, const month& m) NOEXCEPT
+{
+    return {y, m};
+}
+
+CONSTCD11
+inline
+year_month
+operator/(const year& y, int   m) NOEXCEPT
+{
+    return y / month(static_cast<unsigned>(m));
+}
+
+// month_day from operator/()
+
+CONSTCD11
+inline
+month_day
+operator/(const month& m, const day& d) NOEXCEPT
+{
+    return {m, d};
+}
+
+CONSTCD11
+inline
+month_day
+operator/(const day& d, const month& m) NOEXCEPT
+{
+    return m / d;
+}
+
+CONSTCD11
+inline
+month_day
+operator/(const month& m, int d) NOEXCEPT
+{
+    return m / day(static_cast<unsigned>(d));
+}
+
+CONSTCD11
+inline
+month_day
+operator/(int m, const day& d) NOEXCEPT
+{
+    return month(static_cast<unsigned>(m)) / d;
+}
+
+CONSTCD11 inline month_day operator/(const day& d, int m) NOEXCEPT {return m / d;}
+
+// month_day_last from operator/()
+
+CONSTCD11
+inline
+month_day_last
+operator/(const month& m, last_spec) NOEXCEPT
+{
+    return month_day_last{m};
+}
+
+CONSTCD11
+inline
+month_day_last
+operator/(last_spec, const month& m) NOEXCEPT
+{
+    return m/last;
+}
+
+CONSTCD11
+inline
+month_day_last
+operator/(int m, last_spec) NOEXCEPT
+{
+    return month(static_cast<unsigned>(m))/last;
+}
+
+CONSTCD11
+inline
+month_day_last
+operator/(last_spec, int m) NOEXCEPT
+{
+    return m/last;
+}
+
+// month_weekday from operator/()
+
+CONSTCD11
+inline
+month_weekday
+operator/(const month& m, const weekday_indexed& wdi) NOEXCEPT
+{
+    return {m, wdi};
+}
+
+CONSTCD11
+inline
+month_weekday
+operator/(const weekday_indexed& wdi, const month& m) NOEXCEPT
+{
+    return m / wdi;
+}
+
+CONSTCD11
+inline
+month_weekday
+operator/(int m, const weekday_indexed& wdi) NOEXCEPT
+{
+    return month(static_cast<unsigned>(m)) / wdi;
+}
+
+CONSTCD11
+inline
+month_weekday
+operator/(const weekday_indexed& wdi, int m) NOEXCEPT
+{
+    return m / wdi;
+}
+
+// month_weekday_last from operator/()
+
+CONSTCD11
+inline
+month_weekday_last
+operator/(const month& m, const weekday_last& wdl) NOEXCEPT
+{
+    return {m, wdl};
+}
+
+CONSTCD11
+inline
+month_weekday_last
+operator/(const weekday_last& wdl, const month& m) NOEXCEPT
+{
+    return m / wdl;
+}
+
+CONSTCD11
+inline
+month_weekday_last
+operator/(int m, const weekday_last& wdl) NOEXCEPT
+{
+    return month(static_cast<unsigned>(m)) / wdl;
+}
+
+CONSTCD11
+inline
+month_weekday_last
+operator/(const weekday_last& wdl, int m) NOEXCEPT
+{
+    return m / wdl;
+}
+
+// year_month_day from operator/()
+
+CONSTCD11
+inline
+year_month_day
+operator/(const year_month& ym, const day& d) NOEXCEPT
+{
+    return {ym.year(), ym.month(), d};
+}
+
+CONSTCD11
+inline
+year_month_day
+operator/(const year_month& ym, int d)  NOEXCEPT
+{
+    return ym / day(static_cast<unsigned>(d));
+}
+
+CONSTCD11
+inline
+year_month_day
+operator/(const year& y, const month_day& md) NOEXCEPT
+{
+    return y / md.month() / md.day();
+}
+
+CONSTCD11
+inline
+year_month_day
+operator/(int y, const month_day& md) NOEXCEPT
+{
+    return year(y) / md;
+}
+
+CONSTCD11
+inline
+year_month_day
+operator/(const month_day& md, const year& y)  NOEXCEPT
+{
+    return y / md;
+}
+
+CONSTCD11
+inline
+year_month_day
+operator/(const month_day& md, int y) NOEXCEPT
+{
+    return year(y) / md;
+}
+
+// year_month_day_last from operator/()
+
+CONSTCD11
+inline
+year_month_day_last
+operator/(const year_month& ym, last_spec) NOEXCEPT
+{
+    return {ym.year(), month_day_last{ym.month()}};
+}
+
+CONSTCD11
+inline
+year_month_day_last
+operator/(const year& y, const month_day_last& mdl) NOEXCEPT
+{
+    return {y, mdl};
+}
+
+CONSTCD11
+inline
+year_month_day_last
+operator/(int y, const month_day_last& mdl) NOEXCEPT
+{
+    return year(y) / mdl;
+}
+
+CONSTCD11
+inline
+year_month_day_last
+operator/(const month_day_last& mdl, const year& y) NOEXCEPT
+{
+    return y / mdl;
+}
+
+CONSTCD11
+inline
+year_month_day_last
+operator/(const month_day_last& mdl, int y) NOEXCEPT
+{
+    return year(y) / mdl;
+}
+
+// year_month_weekday from operator/()
+
+CONSTCD11
+inline
+year_month_weekday
+operator/(const year_month& ym, const weekday_indexed& wdi) NOEXCEPT
+{
+    return {ym.year(), ym.month(), wdi};
+}
+
+CONSTCD11
+inline
+year_month_weekday
+operator/(const year& y, const month_weekday& mwd) NOEXCEPT
+{
+    return {y, mwd.month(), mwd.weekday_indexed()};
+}
+
+CONSTCD11
+inline
+year_month_weekday
+operator/(int y, const month_weekday& mwd) NOEXCEPT
+{
+    return year(y) / mwd;
+}
+
+CONSTCD11
+inline
+year_month_weekday
+operator/(const month_weekday& mwd, const year& y) NOEXCEPT
+{
+    return y / mwd;
+}
+
+CONSTCD11
+inline
+year_month_weekday
+operator/(const month_weekday& mwd, int y) NOEXCEPT
+{
+    return year(y) / mwd;
+}
+
+// year_month_weekday_last from operator/()
+
+CONSTCD11
+inline
+year_month_weekday_last
+operator/(const year_month& ym, const weekday_last& wdl) NOEXCEPT
+{
+    return {ym.year(), ym.month(), wdl};
+}
+
+CONSTCD11
+inline
+year_month_weekday_last
+operator/(const year& y, const month_weekday_last& mwdl) NOEXCEPT
+{
+    return {y, mwdl.month(), mwdl.weekday_last()};
+}
+
+CONSTCD11
+inline
+year_month_weekday_last
+operator/(int y, const month_weekday_last& mwdl) NOEXCEPT
+{
+    return year(y) / mwdl;
+}
+
+CONSTCD11
+inline
+year_month_weekday_last
+operator/(const month_weekday_last& mwdl, const year& y) NOEXCEPT
+{
+    return y / mwdl;
+}
+
+CONSTCD11
+inline
+year_month_weekday_last
+operator/(const month_weekday_last& mwdl, int y) NOEXCEPT
+{
+    return year(y) / mwdl;
+}
+
+template <class Duration>
+struct fields;
+
+template <class CharT, class Traits, class Duration>
+std::basic_ostream<CharT, Traits>&
+to_stream(std::basic_ostream<CharT, Traits>& os, const CharT* fmt,
+          const fields<Duration>& fds, const std::string* abbrev = nullptr,
+          const std::chrono::seconds* offset_sec = nullptr);
+
+template <class CharT, class Traits, class Duration, class Alloc>
+std::basic_istream<CharT, Traits>&
+from_stream(std::basic_istream<CharT, Traits>& is, const CharT* fmt,
+            fields<Duration>& fds, std::basic_string<CharT, Traits, Alloc>* abbrev = nullptr,
+            std::chrono::minutes* offset = nullptr);
+
+// hh_mm_ss
+
+namespace detail
+{
+
+struct undocumented {explicit undocumented() = default;};
+
+// width<n>::value is the number of fractional decimal digits in 1/n
+// width<0>::value and width<1>::value are defined to be 0
+// If 1/n takes more than 18 fractional decimal digits,
+//   the result is truncated to 19.
+// Example:  width<2>::value    ==  1
+// Example:  width<3>::value    == 19
+// Example:  width<4>::value    ==  2
+// Example:  width<10>::value   ==  1
+// Example:  width<1000>::value ==  3
+template <std::uint64_t n, std::uint64_t d, unsigned w = 0,
+          bool should_continue = n%d != 0 && (w < 19)>
+struct width
+{
+    static_assert(d > 0, "width called with zero denominator");
+    static CONSTDATA unsigned value = 1 + width<n%d*10, d, w+1>::value;
+};
+
+template <std::uint64_t n, std::uint64_t d, unsigned w>
+struct width<n, d, w, false>
+{
+    static CONSTDATA unsigned value = 0;
+};
+
+template <unsigned exp>
+struct static_pow10
+{
+private:
+    static CONSTDATA std::uint64_t h = static_pow10<exp/2>::value;
+public:
+    static CONSTDATA std::uint64_t value = h * h * (exp % 2 ? 10 : 1);
+};
+
+template <>
+struct static_pow10<0>
+{
+    static CONSTDATA std::uint64_t value = 1;
+};
+
+template <class Duration>
+class decimal_format_seconds
+{
+    using CT = typename std::common_type<Duration, std::chrono::seconds>::type;
+    using rep = typename CT::rep;
+    static unsigned CONSTDATA trial_width =
+        detail::width<CT::period::num, CT::period::den>::value;
+public:
+    static unsigned CONSTDATA width = trial_width < 19 ? trial_width : 6u;
+    using precision = std::chrono::duration<rep,
+                                            std::ratio<1, static_pow10<width>::value>>;
+
+private:
+    std::chrono::seconds s_;
+    precision            sub_s_;
+
+public:
+    CONSTCD11 decimal_format_seconds()
+        : s_()
+        , sub_s_()
+        {}
+
+    CONSTCD11 explicit decimal_format_seconds(const Duration& d) NOEXCEPT
+        : s_(std::chrono::duration_cast<std::chrono::seconds>(d))
+        , sub_s_(std::chrono::duration_cast<precision>(d - s_))
+        {}
+
+    CONSTCD14 std::chrono::seconds& seconds() NOEXCEPT {return s_;}
+    CONSTCD11 std::chrono::seconds seconds() const NOEXCEPT {return s_;}
+    CONSTCD11 precision subseconds() const NOEXCEPT {return sub_s_;}
+
+    CONSTCD14 precision to_duration() const NOEXCEPT
+    {
+        return s_ + sub_s_;
+    }
+
+    CONSTCD11 bool in_conventional_range() const NOEXCEPT
+    {
+        return sub_s_ < std::chrono::seconds{1} && s_ < std::chrono::minutes{1};
+    }
+
+    template <class CharT, class Traits>
+    friend
+    std::basic_ostream<CharT, Traits>&
+    operator<<(std::basic_ostream<CharT, Traits>& os, const decimal_format_seconds& x)
+    {
+        return x.print(os, std::chrono::treat_as_floating_point<rep>{});
+    }
+
+    template <class CharT, class Traits>
+    std::basic_ostream<CharT, Traits>&
+    print(std::basic_ostream<CharT, Traits>& os, std::true_type) const
+    {
+        date::detail::save_ostream<CharT, Traits> _(os);
+        std::chrono::duration<rep> d = s_ + sub_s_;
+        if (d < std::chrono::seconds{10})
+            os << '0';
+        os.precision(width+6);
+        os << std::fixed << d.count();
+        return os;
+    }
+
+    template <class CharT, class Traits>
+    std::basic_ostream<CharT, Traits>&
+    print(std::basic_ostream<CharT, Traits>& os, std::false_type) const
+    {
+        date::detail::save_ostream<CharT, Traits> _(os);
+        os.fill('0');
+        os.flags(std::ios::dec | std::ios::right);
+        os.width(2);
+        os << s_.count();
+        if (width > 0)
+        {
+#if !ONLY_C_LOCALE
+            os << std::use_facet<std::numpunct<CharT>>(os.getloc()).decimal_point();
+#else
+            os << '.';
+#endif
+            date::detail::save_ostream<CharT, Traits> _s(os);
+            os.imbue(std::locale::classic());
+            os.width(width);
+            os << sub_s_.count();
+        }
+        return os;
+    }
+};
+
+template <class Rep, class Period>
+inline
+CONSTCD11
+typename std::enable_if
+         <
+            std::numeric_limits<Rep>::is_signed,
+            std::chrono::duration<Rep, Period>
+         >::type
+abs(std::chrono::duration<Rep, Period> d)
+{
+    return d >= d.zero() ? +d : -d;
+}
+
+template <class Rep, class Period>
+inline
+CONSTCD11
+typename std::enable_if
+         <
+            !std::numeric_limits<Rep>::is_signed,
+            std::chrono::duration<Rep, Period>
+         >::type
+abs(std::chrono::duration<Rep, Period> d)
+{
+    return d;
+}
+
+}  // namespace detail
+
+template <class Duration>
+class hh_mm_ss
+{
+    using dfs = detail::decimal_format_seconds<typename std::common_type<Duration,
+                                               std::chrono::seconds>::type>;
+
+    std::chrono::hours h_;
+    std::chrono::minutes m_;
+    dfs s_;
+    bool neg_;
+
+public:
+    static unsigned CONSTDATA fractional_width = dfs::width;
+    using precision = typename dfs::precision;
+
+    CONSTCD11 hh_mm_ss() NOEXCEPT
+        : hh_mm_ss(Duration::zero())
+        {}
+
+    CONSTCD11 explicit hh_mm_ss(Duration d) NOEXCEPT
+        : h_(std::chrono::duration_cast<std::chrono::hours>(detail::abs(d)))
+        , m_(std::chrono::duration_cast<std::chrono::minutes>(detail::abs(d)) - h_)
+        , s_(detail::abs(d) - h_ - m_)
+        , neg_(d < Duration::zero())
+        {}
+
+    CONSTCD11 std::chrono::hours hours() const NOEXCEPT {return h_;}
+    CONSTCD11 std::chrono::minutes minutes() const NOEXCEPT {return m_;}
+    CONSTCD11 std::chrono::seconds seconds() const NOEXCEPT {return s_.seconds();}
+    CONSTCD14 std::chrono::seconds&
+        seconds(detail::undocumented) NOEXCEPT {return s_.seconds();}
+    CONSTCD11 precision subseconds() const NOEXCEPT {return s_.subseconds();}
+    CONSTCD11 bool is_negative() const NOEXCEPT {return neg_;}
+
+    CONSTCD11 explicit operator  precision()   const NOEXCEPT {return to_duration();}
+    CONSTCD11          precision to_duration() const NOEXCEPT
+        {return (s_.to_duration() + m_ + h_) * (1-2*neg_);}
+
+    CONSTCD11 bool in_conventional_range() const NOEXCEPT
+    {
+        return !neg_ && h_ < days{1} && m_ < std::chrono::hours{1} &&
+               s_.in_conventional_range();
+    }
+
+private:
+
+    template <class charT, class traits>
+    friend
+    std::basic_ostream<charT, traits>&
+    operator<<(std::basic_ostream<charT, traits>& os, hh_mm_ss const& tod)
+    {
+        if (tod.is_negative())
+            os << '-';
+        if (tod.h_ < std::chrono::hours{10})
+            os << '0';
+        os << tod.h_.count() << ':';
+        if (tod.m_ < std::chrono::minutes{10})
+            os << '0';
+        os << tod.m_.count() << ':' << tod.s_;
+        return os;
+    }
+
+    template <class CharT, class Traits, class Duration2>
+    friend
+    std::basic_ostream<CharT, Traits>&
+    date::to_stream(std::basic_ostream<CharT, Traits>& os, const CharT* fmt,
+          const fields<Duration2>& fds, const std::string* abbrev,
+          const std::chrono::seconds* offset_sec);
+
+    template <class CharT, class Traits, class Duration2, class Alloc>
+    friend
+    std::basic_istream<CharT, Traits>&
+    date::from_stream(std::basic_istream<CharT, Traits>& is, const CharT* fmt,
+          fields<Duration2>& fds,
+          std::basic_string<CharT, Traits, Alloc>* abbrev, std::chrono::minutes* offset);
+};
+
+inline
+CONSTCD14
+bool
+is_am(std::chrono::hours const& h) NOEXCEPT
+{
+    using std::chrono::hours;
+    return hours{0} <= h && h < hours{12};
+}
+
+inline
+CONSTCD14
+bool
+is_pm(std::chrono::hours const& h) NOEXCEPT
+{
+    using std::chrono::hours;
+    return hours{12} <= h && h < hours{24};
+}
+
+inline
+CONSTCD14
+std::chrono::hours
+make12(std::chrono::hours h) NOEXCEPT
+{
+    using std::chrono::hours;
+    if (h < hours{12})
+    {
+        if (h == hours{0})
+            h = hours{12};
+    }
+    else
+    {
+        if (h != hours{12})
+            h = h - hours{12};
+    }
+    return h;
+}
+
+inline
+CONSTCD14
+std::chrono::hours
+make24(std::chrono::hours h, bool is_pm) NOEXCEPT
+{
+    using std::chrono::hours;
+    if (is_pm)
+    {
+        if (h != hours{12})
+            h = h + hours{12};
+    }
+    else if (h == hours{12})
+        h = hours{0};
+    return h;
+}
+
+template <class Duration>
+using time_of_day = hh_mm_ss<Duration>;
+
+template <class Rep, class Period>
+CONSTCD11
+inline
+hh_mm_ss<std::chrono::duration<Rep, Period>>
+make_time(const std::chrono::duration<Rep, Period>& d)
+{
+    return hh_mm_ss<std::chrono::duration<Rep, Period>>(d);
+}
+
+template <class CharT, class Traits, class Duration>
+inline
+typename std::enable_if
+<
+    std::ratio_less<typename Duration::period, days::period>::value
+    , std::basic_ostream<CharT, Traits>&
+>::type
+operator<<(std::basic_ostream<CharT, Traits>& os, const sys_time<Duration>& tp)
+{
+    auto const dp = date::floor<days>(tp);
+    return os << year_month_day(dp) << ' ' << make_time(tp-dp);
+}
+
+template <class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const sys_days& dp)
+{
+    return os << year_month_day(dp);
+}
+
+template <class CharT, class Traits, class Duration>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const local_time<Duration>& ut)
+{
+    return (os << sys_time<Duration>{ut.time_since_epoch()});
+}
+
+namespace detail
+{
+
+template <class CharT, std::size_t N>
+class string_literal;
+
+template <class CharT1, class CharT2, std::size_t N1, std::size_t N2>
+inline
+CONSTCD14
+string_literal<typename std::conditional<sizeof(CharT2) <= sizeof(CharT1), CharT1, CharT2>::type,
+               N1 + N2 - 1>
+operator+(const string_literal<CharT1, N1>& x, const string_literal<CharT2, N2>& y) NOEXCEPT;
+
+template <class CharT, std::size_t N>
+class string_literal
+{
+    CharT p_[N];
+
+    CONSTCD11 string_literal() NOEXCEPT
+      : p_{}
+    {}
+
+public:
+    using const_iterator = const CharT*;
+
+    string_literal(string_literal const&) = default;
+    string_literal& operator=(string_literal const&) = delete;
+
+    template <std::size_t N1 = 2,
+              class = typename std::enable_if<N1 == N>::type>
+    CONSTCD11 string_literal(CharT c) NOEXCEPT
+        : p_{c}
+    {
+    }
+
+    template <std::size_t N1 = 3,
+              class = typename std::enable_if<N1 == N>::type>
+    CONSTCD11 string_literal(CharT c1, CharT c2) NOEXCEPT
+        : p_{c1, c2}
+    {
+    }
+
+    template <std::size_t N1 = 4,
+              class = typename std::enable_if<N1 == N>::type>
+    CONSTCD11 string_literal(CharT c1, CharT c2, CharT c3) NOEXCEPT
+        : p_{c1, c2, c3}
+    {
+    }
+
+    CONSTCD14 string_literal(const CharT(&a)[N]) NOEXCEPT
+        : p_{}
+    {
+        for (std::size_t i = 0; i < N; ++i)
+            p_[i] = a[i];
+    }
+
+    template <class U = CharT,
+              class = typename std::enable_if<(1 < sizeof(U))>::type>
+    CONSTCD14 string_literal(const char(&a)[N]) NOEXCEPT
+        : p_{}
+    {
+        for (std::size_t i = 0; i < N; ++i)
+            p_[i] = a[i];
+    }
+
+    template <class CharT2,
+              class = typename std::enable_if<!std::is_same<CharT2, CharT>::value>::type>
+    CONSTCD14 string_literal(string_literal<CharT2, N> const& a) NOEXCEPT
+        : p_{}
+    {
+        for (std::size_t i = 0; i < N; ++i)
+            p_[i] = a[i];
+    }
+
+    CONSTCD11 const CharT* data() const NOEXCEPT {return p_;}
+    CONSTCD11 std::size_t size() const NOEXCEPT {return N-1;}
+
+    CONSTCD11 const_iterator begin() const NOEXCEPT {return p_;}
+    CONSTCD11 const_iterator end()   const NOEXCEPT {return p_ + N-1;}
+
+    CONSTCD11 CharT const& operator[](std::size_t n) const NOEXCEPT
+    {
+        return p_[n];
+    }
+
+    template <class Traits>
+    friend
+    std::basic_ostream<CharT, Traits>&
+    operator<<(std::basic_ostream<CharT, Traits>& os, const string_literal& s)
+    {
+        return os << s.p_;
+    }
+
+    template <class CharT1, class CharT2, std::size_t N1, std::size_t N2>
+    friend
+    CONSTCD14
+    string_literal<typename std::conditional<sizeof(CharT2) <= sizeof(CharT1), CharT1, CharT2>::type,
+                   N1 + N2 - 1>
+    operator+(const string_literal<CharT1, N1>& x, const string_literal<CharT2, N2>& y) NOEXCEPT;
+};
+
+template <class CharT>
+CONSTCD11
+inline
+string_literal<CharT, 3>
+operator+(const string_literal<CharT, 2>& x, const string_literal<CharT, 2>& y) NOEXCEPT
+{
+  return string_literal<CharT, 3>(x[0], y[0]);
+}
+
+template <class CharT>
+CONSTCD11
+inline
+string_literal<CharT, 4>
+operator+(const string_literal<CharT, 3>& x, const string_literal<CharT, 2>& y) NOEXCEPT
+{
+  return string_literal<CharT, 4>(x[0], x[1], y[0]);
+}
+
+template <class CharT1, class CharT2, std::size_t N1, std::size_t N2>
+CONSTCD14
+inline
+string_literal<typename std::conditional<sizeof(CharT2) <= sizeof(CharT1), CharT1, CharT2>::type,
+               N1 + N2 - 1>
+operator+(const string_literal<CharT1, N1>& x, const string_literal<CharT2, N2>& y) NOEXCEPT
+{
+    using CT = typename std::conditional<sizeof(CharT2) <= sizeof(CharT1), CharT1, CharT2>::type;
+
+    string_literal<CT, N1 + N2 - 1> r;
+    std::size_t i = 0;
+    for (; i < N1-1; ++i)
+       r.p_[i] = CT(x.p_[i]);
+    for (std::size_t j = 0; j < N2; ++j, ++i)
+       r.p_[i] = CT(y.p_[j]);
+
+    return r;
+}
+
+
+template <class CharT, class Traits, class Alloc, std::size_t N>
+inline
+std::basic_string<CharT, Traits, Alloc>
+operator+(std::basic_string<CharT, Traits, Alloc> x, const string_literal<CharT, N>& y)
+{
+    x.append(y.data(), y.size());
+    return x;
+}
+
+#if __cplusplus >= 201402  && (!defined(__EDG_VERSION__) || __EDG_VERSION__ > 411) \
+                           && (!defined(__SUNPRO_CC) || __SUNPRO_CC > 0x5150)
+
+template <class CharT,
+          class = std::enable_if_t<std::is_same<CharT, char>::value ||
+                                   std::is_same<CharT, wchar_t>::value ||
+                                   std::is_same<CharT, char16_t>::value ||
+                                   std::is_same<CharT, char32_t>::value>>
+CONSTCD14
+inline
+string_literal<CharT, 2>
+msl(CharT c) NOEXCEPT
+{
+    return string_literal<CharT, 2>{c};
+}
+
+CONSTCD14
+inline
+std::size_t
+to_string_len(std::intmax_t i)
+{
+    std::size_t r = 0;
+    do
+    {
+        i /= 10;
+        ++r;
+    } while (i > 0);
+    return r;
+}
+
+template <std::intmax_t N>
+CONSTCD14
+inline
+std::enable_if_t
+<
+    N < 10,
+    string_literal<char, to_string_len(N)+1>
+>
+msl() NOEXCEPT
+{
+    return msl(char(N % 10 + '0'));
+}
+
+template <std::intmax_t N>
+CONSTCD14
+inline
+std::enable_if_t
+<
+    10 <= N,
+    string_literal<char, to_string_len(N)+1>
+>
+msl() NOEXCEPT
+{
+    return msl<N/10>() + msl(char(N % 10 + '0'));
+}
+
+template <class CharT, std::intmax_t N, std::intmax_t D>
+CONSTCD14
+inline
+std::enable_if_t
+<
+    std::ratio<N, D>::type::den != 1,
+    string_literal<CharT, to_string_len(std::ratio<N, D>::type::num) +
+                          to_string_len(std::ratio<N, D>::type::den) + 4>
+>
+msl(std::ratio<N, D>) NOEXCEPT
+{
+    using R = typename std::ratio<N, D>::type;
+    return msl(CharT{'['}) + msl<R::num>() + msl(CharT{'/'}) +
+                             msl<R::den>() + msl(CharT{']'});
+}
+
+template <class CharT, std::intmax_t N, std::intmax_t D>
+CONSTCD14
+inline
+std::enable_if_t
+<
+    std::ratio<N, D>::type::den == 1,
+    string_literal<CharT, to_string_len(std::ratio<N, D>::type::num) + 3>
+>
+msl(std::ratio<N, D>) NOEXCEPT
+{
+    using R = typename std::ratio<N, D>::type;
+    return msl(CharT{'['}) + msl<R::num>() + msl(CharT{']'});
+}
+
+
+#else  // __cplusplus < 201402 || (defined(__EDG_VERSION__) && __EDG_VERSION__ <= 411)
+
+inline
+std::string
+to_string(std::uint64_t x)
+{
+    return std::to_string(x);
+}
+
+template <class CharT>
+inline
+std::basic_string<CharT>
+to_string(std::uint64_t x)
+{
+    auto y = std::to_string(x);
+    return std::basic_string<CharT>(y.begin(), y.end());
+}
+
+template <class CharT, std::intmax_t N, std::intmax_t D>
+inline
+typename std::enable_if
+<
+    std::ratio<N, D>::type::den != 1,
+    std::basic_string<CharT>
+>::type
+msl(std::ratio<N, D>)
+{
+    using R = typename std::ratio<N, D>::type;
+    return std::basic_string<CharT>(1, '[') + to_string<CharT>(R::num) + CharT{'/'} +
+                                              to_string<CharT>(R::den) + CharT{']'};
+}
+
+template <class CharT, std::intmax_t N, std::intmax_t D>
+inline
+typename std::enable_if
+<
+    std::ratio<N, D>::type::den == 1,
+    std::basic_string<CharT>
+>::type
+msl(std::ratio<N, D>)
+{
+    using R = typename std::ratio<N, D>::type;
+    return std::basic_string<CharT>(1, '[') + to_string<CharT>(R::num) + CharT{']'};
+}
+
+#endif  // __cplusplus < 201402 || (defined(__EDG_VERSION__) && __EDG_VERSION__ <= 411)
+
+template <class CharT>
+CONSTCD11
+inline
+string_literal<CharT, 2>
+msl(std::atto) NOEXCEPT
+{
+    return string_literal<CharT, 2>{'a'};
+}
+
+template <class CharT>
+CONSTCD11
+inline
+string_literal<CharT, 2>
+msl(std::femto) NOEXCEPT
+{
+    return string_literal<CharT, 2>{'f'};
+}
+
+template <class CharT>
+CONSTCD11
+inline
+string_literal<CharT, 2>
+msl(std::pico) NOEXCEPT
+{
+    return string_literal<CharT, 2>{'p'};
+}
+
+template <class CharT>
+CONSTCD11
+inline
+string_literal<CharT, 2>
+msl(std::nano) NOEXCEPT
+{
+    return string_literal<CharT, 2>{'n'};
+}
+
+template <class CharT>
+CONSTCD11
+inline
+typename std::enable_if
+<
+    std::is_same<CharT, char>::value,
+    string_literal<char, 3>
+>::type
+msl(std::micro) NOEXCEPT
+{
+    return string_literal<char, 3>{'\xC2', '\xB5'};
+}
+
+template <class CharT>
+CONSTCD11
+inline
+typename std::enable_if
+<
+    !std::is_same<CharT, char>::value,
+    string_literal<CharT, 2>
+>::type
+msl(std::micro) NOEXCEPT
+{
+    return string_literal<CharT, 2>{CharT{static_cast<unsigned char>('\xB5')}};
+}
+
+template <class CharT>
+CONSTCD11
+inline
+string_literal<CharT, 2>
+msl(std::milli) NOEXCEPT
+{
+    return string_literal<CharT, 2>{'m'};
+}
+
+template <class CharT>
+CONSTCD11
+inline
+string_literal<CharT, 2>
+msl(std::centi) NOEXCEPT
+{
+    return string_literal<CharT, 2>{'c'};
+}
+
+template <class CharT>
+CONSTCD11
+inline
+string_literal<CharT, 3>
+msl(std::deca) NOEXCEPT
+{
+    return string_literal<CharT, 3>{'d', 'a'};
+}
+
+template <class CharT>
+CONSTCD11
+inline
+string_literal<CharT, 2>
+msl(std::deci) NOEXCEPT
+{
+    return string_literal<CharT, 2>{'d'};
+}
+
+template <class CharT>
+CONSTCD11
+inline
+string_literal<CharT, 2>
+msl(std::hecto) NOEXCEPT
+{
+    return string_literal<CharT, 2>{'h'};
+}
+
+template <class CharT>
+CONSTCD11
+inline
+string_literal<CharT, 2>
+msl(std::kilo) NOEXCEPT
+{
+    return string_literal<CharT, 2>{'k'};
+}
+
+template <class CharT>
+CONSTCD11
+inline
+string_literal<CharT, 2>
+msl(std::mega) NOEXCEPT
+{
+    return string_literal<CharT, 2>{'M'};
+}
+
+template <class CharT>
+CONSTCD11
+inline
+string_literal<CharT, 2>
+msl(std::giga) NOEXCEPT
+{
+    return string_literal<CharT, 2>{'G'};
+}
+
+template <class CharT>
+CONSTCD11
+inline
+string_literal<CharT, 2>
+msl(std::tera) NOEXCEPT
+{
+    return string_literal<CharT, 2>{'T'};
+}
+
+template <class CharT>
+CONSTCD11
+inline
+string_literal<CharT, 2>
+msl(std::peta) NOEXCEPT
+{
+    return string_literal<CharT, 2>{'P'};
+}
+
+template <class CharT>
+CONSTCD11
+inline
+string_literal<CharT, 2>
+msl(std::exa) NOEXCEPT
+{
+    return string_literal<CharT, 2>{'E'};
+}
+
+template <class CharT, class Period>
+CONSTCD11
+inline
+auto
+get_units(Period p)
+ -> decltype(msl<CharT>(p) + string_literal<CharT, 2>{'s'})
+{
+    return msl<CharT>(p) + string_literal<CharT, 2>{'s'};
+}
+
+template <class CharT>
+CONSTCD11
+inline
+string_literal<CharT, 2>
+get_units(std::ratio<1>)
+{
+    return string_literal<CharT, 2>{'s'};
+}
+
+template <class CharT>
+CONSTCD11
+inline
+string_literal<CharT, 2>
+get_units(std::ratio<3600>)
+{
+    return string_literal<CharT, 2>{'h'};
+}
+
+template <class CharT>
+CONSTCD11
+inline
+string_literal<CharT, 4>
+get_units(std::ratio<60>)
+{
+    return string_literal<CharT, 4>{'m', 'i', 'n'};
+}
+
+template <class CharT>
+CONSTCD11
+inline
+string_literal<CharT, 2>
+get_units(std::ratio<86400>)
+{
+    return string_literal<CharT, 2>{'d'};
+}
+
+template <class CharT, class Traits = std::char_traits<CharT>>
+struct make_string;
+
+template <>
+struct make_string<char>
+{
+    template <class Rep>
+    static
+    std::string
+    from(Rep n)
+    {
+        return std::to_string(n);
+    }
+};
+
+template <class Traits>
+struct make_string<char, Traits>
+{
+    template <class Rep>
+    static
+    std::basic_string<char, Traits>
+    from(Rep n)
+    {
+        auto s = std::to_string(n);
+        return std::basic_string<char, Traits>(s.begin(), s.end());
+    }
+};
+
+template <>
+struct make_string<wchar_t>
+{
+    template <class Rep>
+    static
+    std::wstring
+    from(Rep n)
+    {
+        return std::to_wstring(n);
+    }
+};
+
+template <class Traits>
+struct make_string<wchar_t, Traits>
+{
+    template <class Rep>
+    static
+    std::basic_string<wchar_t, Traits>
+    from(Rep n)
+    {
+        auto s = std::to_wstring(n);
+        return std::basic_string<wchar_t, Traits>(s.begin(), s.end());
+    }
+};
+
+}  // namespace detail
+
+// to_stream
+
+CONSTDATA year nanyear{-32768};
+
+template <class Duration>
+struct fields
+{
+    year_month_day        ymd{nanyear/0/0};
+    weekday               wd{8u};
+    hh_mm_ss<Duration>    tod{};
+    bool                  has_tod = false;
+
+    fields() = default;
+
+    fields(year_month_day ymd_) : ymd(ymd_) {}
+    fields(weekday wd_) : wd(wd_) {}
+    fields(hh_mm_ss<Duration> tod_) : tod(tod_), has_tod(true) {}
+
+    fields(year_month_day ymd_, weekday wd_) : ymd(ymd_), wd(wd_) {}
+    fields(year_month_day ymd_, hh_mm_ss<Duration> tod_) : ymd(ymd_), tod(tod_),
+                                                           has_tod(true) {}
+
+    fields(weekday wd_, hh_mm_ss<Duration> tod_) : wd(wd_), tod(tod_), has_tod(true) {}
+
+    fields(year_month_day ymd_, weekday wd_, hh_mm_ss<Duration> tod_)
+        : ymd(ymd_)
+        , wd(wd_)
+        , tod(tod_)
+        , has_tod(true)
+        {}
+};
+
+namespace detail
+{
+
+template <class CharT, class Traits, class Duration>
+unsigned
+extract_weekday(std::basic_ostream<CharT, Traits>& os, const fields<Duration>& fds)
+{
+    if (!fds.ymd.ok() && !fds.wd.ok())
+    {
+        // fds does not contain a valid weekday
+        os.setstate(std::ios::failbit);
+        return 8;
+    }
+    weekday wd;
+    if (fds.ymd.ok())
+    {
+        wd = weekday{sys_days(fds.ymd)};
+        if (fds.wd.ok() && wd != fds.wd)
+        {
+            // fds.ymd and fds.wd are inconsistent
+            os.setstate(std::ios::failbit);
+            return 8;
+        }
+    }
+    else
+        wd = fds.wd;
+    return static_cast<unsigned>((wd - Sunday).count());
+}
+
+template <class CharT, class Traits, class Duration>
+unsigned
+extract_month(std::basic_ostream<CharT, Traits>& os, const fields<Duration>& fds)
+{
+    if (!fds.ymd.month().ok())
+    {
+        // fds does not contain a valid month
+        os.setstate(std::ios::failbit);
+        return 0;
+    }
+    return static_cast<unsigned>(fds.ymd.month());
+}
+
+}  // namespace detail
+
+#if ONLY_C_LOCALE
+
+namespace detail
+{
+
+inline
+std::pair<const std::string*, const std::string*>
+weekday_names()
+{
+    static const std::string nm[] =
+    {
+        "Sunday",
+        "Monday",
+        "Tuesday",
+        "Wednesday",
+        "Thursday",
+        "Friday",
+        "Saturday",
+        "Sun",
+        "Mon",
+        "Tue",
+        "Wed",
+        "Thu",
+        "Fri",
+        "Sat"
+    };
+    return std::make_pair(nm, nm+sizeof(nm)/sizeof(nm[0]));
+}
+
+inline
+std::pair<const std::string*, const std::string*>
+month_names()
+{
+    static const std::string nm[] =
+    {
+        "January",
+        "February",
+        "March",
+        "April",
+        "May",
+        "June",
+        "July",
+        "August",
+        "September",
+        "October",
+        "November",
+        "December",
+        "Jan",
+        "Feb",
+        "Mar",
+        "Apr",
+        "May",
+        "Jun",
+        "Jul",
+        "Aug",
+        "Sep",
+        "Oct",
+        "Nov",
+        "Dec"
+    };
+    return std::make_pair(nm, nm+sizeof(nm)/sizeof(nm[0]));
+}
+
+inline
+std::pair<const std::string*, const std::string*>
+ampm_names()
+{
+    static const std::string nm[] =
+    {
+        "AM",
+        "PM"
+    };
+    return std::make_pair(nm, nm+sizeof(nm)/sizeof(nm[0]));
+}
+
+template <class CharT, class Traits, class FwdIter>
+FwdIter
+scan_keyword(std::basic_istream<CharT, Traits>& is, FwdIter kb, FwdIter ke)
+{
+    size_t nkw = static_cast<size_t>(std::distance(kb, ke));
+    const unsigned char doesnt_match = '\0';
+    const unsigned char might_match = '\1';
+    const unsigned char does_match = '\2';
+    unsigned char statbuf[100];
+    unsigned char* status = statbuf;
+    std::unique_ptr<unsigned char, void(*)(void*)> stat_hold(0, free);
+    if (nkw > sizeof(statbuf))
+    {
+        status = (unsigned char*)std::malloc(nkw);
+        if (status == nullptr)
+            throw std::bad_alloc();
+        stat_hold.reset(status);
+    }
+    size_t n_might_match = nkw;  // At this point, any keyword might match
+    size_t n_does_match = 0;     // but none of them definitely do
+    // Initialize all statuses to might_match, except for "" keywords are does_match
+    unsigned char* st = status;
+    for (auto ky = kb; ky != ke; ++ky, ++st)
+    {
+        if (!ky->empty())
+            *st = might_match;
+        else
+        {
+            *st = does_match;
+            --n_might_match;
+            ++n_does_match;
+        }
+    }
+    // While there might be a match, test keywords against the next CharT
+    for (size_t indx = 0; is && n_might_match > 0; ++indx)
+    {
+        // Peek at the next CharT but don't consume it
+        auto ic = is.peek();
+        if (ic == EOF)
+        {
+            is.setstate(std::ios::eofbit);
+            break;
+        }
+        auto c = static_cast<char>(toupper(static_cast<unsigned char>(ic)));
+        bool consume = false;
+        // For each keyword which might match, see if the indx character is c
+        // If a match if found, consume c
+        // If a match is found, and that is the last character in the keyword,
+        //    then that keyword matches.
+        // If the keyword doesn't match this character, then change the keyword
+        //    to doesn't match
+        st = status;
+        for (auto ky = kb; ky != ke; ++ky, ++st)
+        {
+            if (*st == might_match)
+            {
+                if (c == static_cast<char>(toupper(static_cast<unsigned char>((*ky)[indx]))))
+                {
+                    consume = true;
+                    if (ky->size() == indx+1)
+                    {
+                        *st = does_match;
+                        --n_might_match;
+                        ++n_does_match;
+                    }
+                }
+                else
+                {
+                    *st = doesnt_match;
+                    --n_might_match;
+                }
+            }
+        }
+        // consume if we matched a character
+        if (consume)
+        {
+            (void)is.get();
+            // If we consumed a character and there might be a matched keyword that
+            //   was marked matched on a previous iteration, then such keywords
+            //   are now marked as not matching.
+            if (n_might_match + n_does_match > 1)
+            {
+                st = status;
+                for (auto ky = kb; ky != ke; ++ky, ++st)
+                {
+                    if (*st == does_match && ky->size() != indx+1)
+                    {
+                        *st = doesnt_match;
+                        --n_does_match;
+                    }
+                }
+            }
+        }
+    }
+    // We've exited the loop because we hit eof and/or we have no more "might matches".
+    // Return the first matching result
+    for (st = status; kb != ke; ++kb, ++st)
+        if (*st == does_match)
+            break;
+    if (kb == ke)
+        is.setstate(std::ios::failbit);
+    return kb;
+}
+
+}  // namespace detail
+
+#endif  // ONLY_C_LOCALE
+
+template <class CharT, class Traits, class Duration>
+std::basic_ostream<CharT, Traits>&
+to_stream(std::basic_ostream<CharT, Traits>& os, const CharT* fmt,
+          const fields<Duration>& fds, const std::string* abbrev,
+          const std::chrono::seconds* offset_sec)
+{
+#if ONLY_C_LOCALE
+    using detail::weekday_names;
+    using detail::month_names;
+    using detail::ampm_names;
+#endif
+    using detail::save_ostream;
+    using detail::get_units;
+    using detail::extract_weekday;
+    using detail::extract_month;
+    using std::ios;
+    using std::chrono::duration_cast;
+    using std::chrono::seconds;
+    using std::chrono::minutes;
+    using std::chrono::hours;
+    date::detail::save_ostream<CharT, Traits> ss(os);
+    os.fill(' ');
+    os.flags(std::ios::skipws | std::ios::dec);
+    os.width(0);
+    tm tm{};
+    bool insert_negative = fds.has_tod && fds.tod.to_duration() < Duration::zero();
+#if !ONLY_C_LOCALE
+    auto& facet = std::use_facet<std::time_put<CharT>>(os.getloc());
+#endif
+    const CharT* command = nullptr;
+    CharT modified = CharT{};
+    for (; *fmt; ++fmt)
+    {
+        switch (*fmt)
+        {
+        case 'a':
+        case 'A':
+            if (command)
+            {
+                if (modified == CharT{})
+                {
+                    tm.tm_wday = static_cast<int>(extract_weekday(os, fds));
+                    if (os.fail())
+                        return os;
+#if !ONLY_C_LOCALE
+                    const CharT f[] = {'%', *fmt};
+                    facet.put(os, os, os.fill(), &tm, std::begin(f), std::end(f));
+#else  // ONLY_C_LOCALE
+                    os << weekday_names().first[tm.tm_wday+7*(*fmt == 'a')];
+#endif  // ONLY_C_LOCALE
+                }
+                else
+                {
+                    os << CharT{'%'} << modified << *fmt;
+                    modified = CharT{};
+                }
+                command = nullptr;
+            }
+            else
+                os << *fmt;
+            break;
+        case 'b':
+        case 'B':
+        case 'h':
+            if (command)
+            {
+                if (modified == CharT{})
+                {
+                    tm.tm_mon = static_cast<int>(extract_month(os, fds)) - 1;
+#if !ONLY_C_LOCALE
+                    const CharT f[] = {'%', *fmt};
+                    facet.put(os, os, os.fill(), &tm, std::begin(f), std::end(f));
+#else  // ONLY_C_LOCALE
+                    os << month_names().first[tm.tm_mon+12*(*fmt != 'B')];
+#endif  // ONLY_C_LOCALE
+                }
+                else
+                {
+                    os << CharT{'%'} << modified << *fmt;
+                    modified = CharT{};
+                }
+                command = nullptr;
+            }
+            else
+                os << *fmt;
+            break;
+        case 'c':
+        case 'x':
+            if (command)
+            {
+                if (modified == CharT{'O'})
+                    os << CharT{'%'} << modified << *fmt;
+                else
+                {
+                    if (!fds.ymd.ok())
+                        os.setstate(std::ios::failbit);
+                    if (*fmt == 'c' && !fds.has_tod)
+                        os.setstate(std::ios::failbit);
+#if !ONLY_C_LOCALE
+                    tm = std::tm{};
+                    auto const& ymd = fds.ymd;
+                    auto ld = local_days(ymd);
+                    if (*fmt == 'c')
+                    {
+                        tm.tm_sec = static_cast<int>(fds.tod.seconds().count());
+                        tm.tm_min = static_cast<int>(fds.tod.minutes().count());
+                        tm.tm_hour = static_cast<int>(fds.tod.hours().count());
+                    }
+                    tm.tm_mday = static_cast<int>(static_cast<unsigned>(ymd.day()));
+                    tm.tm_mon = static_cast<int>(extract_month(os, fds) - 1);
+                    tm.tm_year = static_cast<int>(ymd.year()) - 1900;
+                    tm.tm_wday = static_cast<int>(extract_weekday(os, fds));
+                    if (os.fail())
+                        return os;
+                    tm.tm_yday = static_cast<int>((ld - local_days(ymd.year()/1/1)).count());
+                    CharT f[3] = {'%'};
+                    auto fe = std::begin(f) + 1;
+                    if (modified == CharT{'E'})
+                        *fe++ = modified;
+                    *fe++ = *fmt;
+                    facet.put(os, os, os.fill(), &tm, std::begin(f), fe);
+#else  // ONLY_C_LOCALE
+                    if (*fmt == 'c')
+                    {
+                        auto wd = static_cast<int>(extract_weekday(os, fds));
+                        os << weekday_names().first[static_cast<unsigned>(wd)+7]
+                           << ' ';
+                        os << month_names().first[extract_month(os, fds)-1+12] << ' ';
+                        auto d = static_cast<int>(static_cast<unsigned>(fds.ymd.day()));
+                        if (d < 10)
+                            os << ' ';
+                        os << d << ' '
+                           << make_time(duration_cast<seconds>(fds.tod.to_duration()))
+                           << ' ' << fds.ymd.year();
+
+                    }
+                    else  // *fmt == 'x'
+                    {
+                        auto const& ymd = fds.ymd;
+                        save_ostream<CharT, Traits> _(os);
+                        os.fill('0');
+                        os.flags(std::ios::dec | std::ios::right);
+                        os.width(2);
+                        os << static_cast<unsigned>(ymd.month()) << CharT{'/'};
+                        os.width(2);
+                        os << static_cast<unsigned>(ymd.day()) << CharT{'/'};
+                        os.width(2);
+                        os << static_cast<int>(ymd.year()) % 100;
+                    }
+#endif  // ONLY_C_LOCALE
+                }
+                command = nullptr;
+                modified = CharT{};
+            }
+            else
+                os << *fmt;
+            break;
+        case 'C':
+            if (command)
+            {
+                if (modified == CharT{'O'})
+                    os << CharT{'%'} << modified << *fmt;
+                else
+                {
+                    if (!fds.ymd.year().ok())
+                        os.setstate(std::ios::failbit);
+                    auto y = static_cast<int>(fds.ymd.year());
+#if !ONLY_C_LOCALE
+                    if (modified == CharT{})
+#endif
+                    {
+                        save_ostream<CharT, Traits> _(os);
+                        os.fill('0');
+                        os.flags(std::ios::dec | std::ios::right);
+                        if (y >= 0)
+                        {
+                            os.width(2);
+                            os << y/100;
+                        }
+                        else
+                        {
+                            os << CharT{'-'};
+                            os.width(2);
+                            os << -(y-99)/100;
+                        }
+                    }
+#if !ONLY_C_LOCALE
+                    else if (modified == CharT{'E'})
+                    {
+                        tm.tm_year = y - 1900;
+                        CharT f[3] = {'%', 'E', 'C'};
+                        facet.put(os, os, os.fill(), &tm, std::begin(f), std::end(f));
+                    }
+#endif
+                }
+                command = nullptr;
+                modified = CharT{};
+            }
+            else
+                os << *fmt;
+            break;
+        case 'd':
+        case 'e':
+            if (command)
+            {
+                if (modified == CharT{'E'})
+                    os << CharT{'%'} << modified << *fmt;
+                else
+                {
+                    if (!fds.ymd.day().ok())
+                        os.setstate(std::ios::failbit);
+                    auto d = static_cast<int>(static_cast<unsigned>(fds.ymd.day()));
+#if !ONLY_C_LOCALE
+                    if (modified == CharT{})
+#endif
+                    {
+                        save_ostream<CharT, Traits> _(os);
+                        if (*fmt == CharT{'d'})
+                            os.fill('0');
+                        else
+                            os.fill(' ');
+                        os.flags(std::ios::dec | std::ios::right);
+                        os.width(2);
+                        os << d;
+                    }
+#if !ONLY_C_LOCALE
+                    else if (modified == CharT{'O'})
+                    {
+                        tm.tm_mday = d;
+                        CharT f[3] = {'%', 'O', *fmt};
+                        facet.put(os, os, os.fill(), &tm, std::begin(f), std::end(f));
+                    }
+#endif
+                }
+                command = nullptr;
+                modified = CharT{};
+            }
+            else
+                os << *fmt;
+            break;
+        case 'D':
+            if (command)
+            {
+                if (modified == CharT{})
+                {
+                    if (!fds.ymd.ok())
+                        os.setstate(std::ios::failbit);
+                    auto const& ymd = fds.ymd;
+                    save_ostream<CharT, Traits> _(os);
+                    os.fill('0');
+                    os.flags(std::ios::dec | std::ios::right);
+                    os.width(2);
+                    os << static_cast<unsigned>(ymd.month()) << CharT{'/'};
+                    os.width(2);
+                    os << static_cast<unsigned>(ymd.day()) << CharT{'/'};
+                    os.width(2);
+                    os << static_cast<int>(ymd.year()) % 100;
+                }
+                else
+                {
+                    os << CharT{'%'} << modified << *fmt;
+                    modified = CharT{};
+                }
+                command = nullptr;
+            }
+            else
+                os << *fmt;
+            break;
+        case 'F':
+            if (command)
+            {
+                if (modified == CharT{})
+                {
+                    if (!fds.ymd.ok())
+                        os.setstate(std::ios::failbit);
+                    auto const& ymd = fds.ymd;
+                    save_ostream<CharT, Traits> _(os);
+                    os.imbue(std::locale::classic());
+                    os.fill('0');
+                    os.flags(std::ios::dec | std::ios::right);
+                    os.width(4);
+                    os << static_cast<int>(ymd.year()) << CharT{'-'};
+                    os.width(2);
+                    os << static_cast<unsigned>(ymd.month()) << CharT{'-'};
+                    os.width(2);
+                    os << static_cast<unsigned>(ymd.day());
+                }
+                else
+                {
+                    os << CharT{'%'} << modified << *fmt;
+                    modified = CharT{};
+                }
+                command = nullptr;
+            }
+            else
+                os << *fmt;
+            break;
+        case 'g':
+        case 'G':
+            if (command)
+            {
+                if (modified == CharT{})
+                {
+                    if (!fds.ymd.ok())
+                        os.setstate(std::ios::failbit);
+                    auto ld = local_days(fds.ymd);
+                    auto y = year_month_day{ld + days{3}}.year();
+                    auto start = local_days((y-years{1})/December/Thursday[last]) +
+                                 (Monday-Thursday);
+                    if (ld < start)
+                        --y;
+                    if (*fmt == CharT{'G'})
+                        os << y;
+                    else
+                    {
+                        save_ostream<CharT, Traits> _(os);
+                        os.fill('0');
+                        os.flags(std::ios::dec | std::ios::right);
+                        os.width(2);
+                        os << std::abs(static_cast<int>(y)) % 100;
+                    }
+                }
+                else
+                {
+                    os << CharT{'%'} << modified << *fmt;
+                    modified = CharT{};
+                }
+                command = nullptr;
+            }
+            else
+                os << *fmt;
+            break;
+        case 'H':
+        case 'I':
+            if (command)
+            {
+                if (modified == CharT{'E'})
+                    os << CharT{'%'} << modified << *fmt;
+                else
+                {
+                    if (!fds.has_tod)
+                        os.setstate(std::ios::failbit);
+                    if (insert_negative)
+                    {
+                        os << '-';
+                        insert_negative = false;
+                    }
+                    auto hms = fds.tod;
+#if !ONLY_C_LOCALE
+                    if (modified == CharT{})
+#endif
+                    {
+                        auto h = *fmt == CharT{'I'} ? date::make12(hms.hours()) : hms.hours();
+                        if (h < hours{10})
+                            os << CharT{'0'};
+                        os << h.count();
+                    }
+#if !ONLY_C_LOCALE
+                    else if (modified == CharT{'O'})
+                    {
+                        const CharT f[] = {'%', modified, *fmt};
+                        tm.tm_hour = static_cast<int>(hms.hours().count());
+                        facet.put(os, os, os.fill(), &tm, std::begin(f), std::end(f));
+                    }
+#endif
+                }
+                modified = CharT{};
+                command = nullptr;
+            }
+            else
+                os << *fmt;
+            break;
+        case 'j':
+            if (command)
+            {
+                if (modified == CharT{})
+                {
+                    if (fds.ymd.ok() || fds.has_tod)
+                    {
+                        days doy;
+                        if (fds.ymd.ok())
+                        {
+                            auto ld = local_days(fds.ymd);
+                            auto y = fds.ymd.year();
+                            doy = ld - local_days(y/January/1) + days{1};
+                        }
+                        else
+                        {
+                            doy = duration_cast<days>(fds.tod.to_duration());
+                        }
+                        save_ostream<CharT, Traits> _(os);
+                        os.fill('0');
+                        os.flags(std::ios::dec | std::ios::right);
+                        os.width(3);
+                        os << doy.count();
+                    }
+                    else
+                    {
+                        os.setstate(std::ios::failbit);
+                    }
+                }
+                else
+                {
+                    os << CharT{'%'} << modified << *fmt;
+                    modified = CharT{};
+                }
+                command = nullptr;
+            }
+            else
+                os << *fmt;
+            break;
+        case 'm':
+            if (command)
+            {
+                if (modified == CharT{'E'})
+                    os << CharT{'%'} << modified << *fmt;
+                else
+                {
+                    if (!fds.ymd.month().ok())
+                        os.setstate(std::ios::failbit);
+                    auto m = static_cast<unsigned>(fds.ymd.month());
+#if !ONLY_C_LOCALE
+                    if (modified == CharT{})
+#endif
+                    {
+                        if (m < 10)
+                            os << CharT{'0'};
+                        os << m;
+                    }
+#if !ONLY_C_LOCALE
+                    else if (modified == CharT{'O'})
+                    {
+                        const CharT f[] = {'%', modified, *fmt};
+                        tm.tm_mon = static_cast<int>(m-1);
+                        facet.put(os, os, os.fill(), &tm, std::begin(f), std::end(f));
+                    }
+#endif
+                }
+                modified = CharT{};
+                command = nullptr;
+            }
+            else
+                os << *fmt;
+            break;
+        case 'M':
+            if (command)
+            {
+                if (modified == CharT{'E'})
+                    os << CharT{'%'} << modified << *fmt;
+                else
+                {
+                    if (!fds.has_tod)
+                        os.setstate(std::ios::failbit);
+                    if (insert_negative)
+                    {
+                        os << '-';
+                        insert_negative = false;
+                    }
+#if !ONLY_C_LOCALE
+                    if (modified == CharT{})
+#endif
+                    {
+                        if (fds.tod.minutes() < minutes{10})
+                            os << CharT{'0'};
+                        os << fds.tod.minutes().count();
+                    }
+#if !ONLY_C_LOCALE
+                    else if (modified == CharT{'O'})
+                    {
+                        const CharT f[] = {'%', modified, *fmt};
+                        tm.tm_min = static_cast<int>(fds.tod.minutes().count());
+                        facet.put(os, os, os.fill(), &tm, std::begin(f), std::end(f));
+                    }
+#endif
+                }
+                modified = CharT{};
+                command = nullptr;
+            }
+            else
+                os << *fmt;
+            break;
+        case 'n':
+            if (command)
+            {
+                if (modified == CharT{})
+                    os << CharT{'\n'};
+                else
+                {
+                    os << CharT{'%'} << modified << *fmt;
+                    modified = CharT{};
+                }
+                command = nullptr;
+            }
+            else
+                os << *fmt;
+            break;
+        case 'p':
+            if (command)
+            {
+                if (modified == CharT{})
+                {
+                    if (!fds.has_tod)
+                        os.setstate(std::ios::failbit);
+#if !ONLY_C_LOCALE
+                    const CharT f[] = {'%', *fmt};
+                    tm.tm_hour = static_cast<int>(fds.tod.hours().count());
+                    facet.put(os, os, os.fill(), &tm, std::begin(f), std::end(f));
+#else
+                    if (date::is_am(fds.tod.hours()))
+                        os << ampm_names().first[0];
+                    else
+                        os << ampm_names().first[1];
+#endif
+                }
+                else
+                {
+                    os << CharT{'%'} << modified << *fmt;
+                }
+                modified = CharT{};
+                command = nullptr;
+            }
+            else
+                os << *fmt;
+            break;
+        case 'Q':
+        case 'q':
+            if (command)
+            {
+                if (modified == CharT{})
+                {
+                    if (!fds.has_tod)
+                        os.setstate(std::ios::failbit);
+                    auto d = fds.tod.to_duration();
+                    if (*fmt == 'q')
+                        os << get_units<CharT>(typename decltype(d)::period::type{});
+                    else
+                        os << d.count();
+                }
+                else
+                {
+                    os << CharT{'%'} << modified << *fmt;
+                }
+                modified = CharT{};
+                command = nullptr;
+            }
+            else
+                os << *fmt;
+            break;
+        case 'r':
+            if (command)
+            {
+                if (modified == CharT{})
+                {
+                    if (!fds.has_tod)
+                        os.setstate(std::ios::failbit);
+#if !ONLY_C_LOCALE
+                    const CharT f[] = {'%', *fmt};
+                    tm.tm_hour = static_cast<int>(fds.tod.hours().count());
+                    tm.tm_min = static_cast<int>(fds.tod.minutes().count());
+                    tm.tm_sec = static_cast<int>(fds.tod.seconds().count());
+                    facet.put(os, os, os.fill(), &tm, std::begin(f), std::end(f));
+#else
+                    hh_mm_ss<seconds> tod(duration_cast<seconds>(fds.tod.to_duration()));
+                    save_ostream<CharT, Traits> _(os);
+                    os.fill('0');
+                    os.width(2);
+                    os << date::make12(tod.hours()).count() << CharT{':'};
+                    os.width(2);
+                    os << tod.minutes().count() << CharT{':'};
+                    os.width(2);
+                    os << tod.seconds().count() << CharT{' '};
+                    if (date::is_am(tod.hours()))
+                        os << ampm_names().first[0];
+                    else
+                        os << ampm_names().first[1];
+#endif
+                }
+                else
+                {
+                    os << CharT{'%'} << modified << *fmt;
+                }
+                modified = CharT{};
+                command = nullptr;
+            }
+            else
+                os << *fmt;
+            break;
+        case 'R':
+            if (command)
+            {
+                if (modified == CharT{})
+                {
+                    if (!fds.has_tod)
+                        os.setstate(std::ios::failbit);
+                    if (fds.tod.hours() < hours{10})
+                        os << CharT{'0'};
+                    os << fds.tod.hours().count() << CharT{':'};
+                    if (fds.tod.minutes() < minutes{10})
+                        os << CharT{'0'};
+                    os << fds.tod.minutes().count();
+                }
+                else
+                {
+                    os << CharT{'%'} << modified << *fmt;
+                    modified = CharT{};
+                }
+                command = nullptr;
+            }
+            else
+                os << *fmt;
+            break;
+        case 'S':
+            if (command)
+            {
+                if (modified == CharT{'E'})
+                    os << CharT{'%'} << modified << *fmt;
+                else
+                {
+                    if (!fds.has_tod)
+                        os.setstate(std::ios::failbit);
+                    if (insert_negative)
+                    {
+                        os << '-';
+                        insert_negative = false;
+                    }
+#if !ONLY_C_LOCALE
+                    if (modified == CharT{})
+#endif
+                    {
+                        os << fds.tod.s_;
+                    }
+#if !ONLY_C_LOCALE
+                    else if (modified == CharT{'O'})
+                    {
+                        const CharT f[] = {'%', modified, *fmt};
+                        tm.tm_sec = static_cast<int>(fds.tod.s_.seconds().count());
+                        facet.put(os, os, os.fill(), &tm, std::begin(f), std::end(f));
+                    }
+#endif
+                }
+                modified = CharT{};
+                command = nullptr;
+            }
+            else
+                os << *fmt;
+            break;
+        case 't':
+            if (command)
+            {
+                if (modified == CharT{})
+                    os << CharT{'\t'};
+                else
+                {
+                    os << CharT{'%'} << modified << *fmt;
+                    modified = CharT{};
+                }
+                command = nullptr;
+            }
+            else
+                os << *fmt;
+            break;
+        case 'T':
+            if (command)
+            {
+                if (modified == CharT{})
+                {
+                    if (!fds.has_tod)
+                        os.setstate(std::ios::failbit);
+                    os << fds.tod;
+                }
+                else
+                {
+                    os << CharT{'%'} << modified << *fmt;
+                    modified = CharT{};
+                }
+                command = nullptr;
+            }
+            else
+                os << *fmt;
+            break;
+        case 'u':
+            if (command)
+            {
+                if (modified == CharT{'E'})
+                    os << CharT{'%'} << modified << *fmt;
+                else
+                {
+                    auto wd = extract_weekday(os, fds);
+#if !ONLY_C_LOCALE
+                    if (modified == CharT{})
+#endif
+                    {
+                        os << (wd != 0 ? wd : 7u);
+                    }
+#if !ONLY_C_LOCALE
+                    else if (modified == CharT{'O'})
+                    {
+                        const CharT f[] = {'%', modified, *fmt};
+                        tm.tm_wday = static_cast<int>(wd);
+                        facet.put(os, os, os.fill(), &tm, std::begin(f), std::end(f));
+                    }
+#endif
+                }
+                modified = CharT{};
+                command = nullptr;
+            }
+            else
+                os << *fmt;
+            break;
+        case 'U':
+            if (command)
+            {
+                if (modified == CharT{'E'})
+                    os << CharT{'%'} << modified << *fmt;
+                else
+                {
+                    auto const& ymd = fds.ymd;
+                    if (!ymd.ok())
+                        os.setstate(std::ios::failbit);
+                    auto ld = local_days(ymd);
+#if !ONLY_C_LOCALE
+                    if (modified == CharT{})
+#endif
+                    {
+                        auto st = local_days(Sunday[1]/January/ymd.year());
+                        if (ld < st)
+                            os << CharT{'0'} << CharT{'0'};
+                        else
+                        {
+                            auto wn = duration_cast<weeks>(ld - st).count() + 1;
+                            if (wn < 10)
+                                os << CharT{'0'};
+                            os << wn;
+                        }
+                   }
+ #if !ONLY_C_LOCALE
+                    else if (modified == CharT{'O'})
+                    {
+                        const CharT f[] = {'%', modified, *fmt};
+                        tm.tm_year = static_cast<int>(ymd.year()) - 1900;
+                        tm.tm_wday = static_cast<int>(extract_weekday(os, fds));
+                        if (os.fail())
+                            return os;
+                        tm.tm_yday = static_cast<int>((ld - local_days(ymd.year()/1/1)).count());
+                        facet.put(os, os, os.fill(), &tm, std::begin(f), std::end(f));
+                    }
+#endif
+                }
+                modified = CharT{};
+                command = nullptr;
+            }
+            else
+                os << *fmt;
+            break;
+        case 'V':
+            if (command)
+            {
+                if (modified == CharT{'E'})
+                    os << CharT{'%'} << modified << *fmt;
+                else
+                {
+                    if (!fds.ymd.ok())
+                        os.setstate(std::ios::failbit);
+                    auto ld = local_days(fds.ymd);
+#if !ONLY_C_LOCALE
+                    if (modified == CharT{})
+#endif
+                    {
+                        auto y = year_month_day{ld + days{3}}.year();
+                        auto st = local_days((y-years{1})/12/Thursday[last]) +
+                                  (Monday-Thursday);
+                        if (ld < st)
+                        {
+                            --y;
+                            st = local_days((y - years{1})/12/Thursday[last]) +
+                                 (Monday-Thursday);
+                        }
+                        auto wn = duration_cast<weeks>(ld - st).count() + 1;
+                        if (wn < 10)
+                            os << CharT{'0'};
+                        os << wn;
+                    }
+#if !ONLY_C_LOCALE
+                    else if (modified == CharT{'O'})
+                    {
+                        const CharT f[] = {'%', modified, *fmt};
+                        auto const& ymd = fds.ymd;
+                        tm.tm_year = static_cast<int>(ymd.year()) - 1900;
+                        tm.tm_wday = static_cast<int>(extract_weekday(os, fds));
+                        if (os.fail())
+                            return os;
+                        tm.tm_yday = static_cast<int>((ld - local_days(ymd.year()/1/1)).count());
+                        facet.put(os, os, os.fill(), &tm, std::begin(f), std::end(f));
+                    }
+#endif
+                }
+                modified = CharT{};
+                command = nullptr;
+            }
+            else
+                os << *fmt;
+            break;
+        case 'w':
+            if (command)
+            {
+                auto wd = extract_weekday(os, fds);
+                if (os.fail())
+                    return os;
+#if !ONLY_C_LOCALE
+                if (modified == CharT{})
+#else
+                if (modified != CharT{'E'})
+#endif
+                {
+                    os << wd;
+                }
+#if !ONLY_C_LOCALE
+                else if (modified == CharT{'O'})
+                {
+                    const CharT f[] = {'%', modified, *fmt};
+                    tm.tm_wday = static_cast<int>(wd);
+                    facet.put(os, os, os.fill(), &tm, std::begin(f), std::end(f));
+                }
+#endif
+                else
+                {
+                    os << CharT{'%'} << modified << *fmt;
+                }
+                modified = CharT{};
+                command = nullptr;
+            }
+            else
+                os << *fmt;
+            break;
+        case 'W':
+            if (command)
+            {
+                if (modified == CharT{'E'})
+                    os << CharT{'%'} << modified << *fmt;
+                else
+                {
+                    auto const& ymd = fds.ymd;
+                    if (!ymd.ok())
+                        os.setstate(std::ios::failbit);
+                    auto ld = local_days(ymd);
+#if !ONLY_C_LOCALE
+                    if (modified == CharT{})
+#endif
+                    {
+                        auto st = local_days(Monday[1]/January/ymd.year());
+                        if (ld < st)
+                            os << CharT{'0'} << CharT{'0'};
+                        else
+                        {
+                            auto wn = duration_cast<weeks>(ld - st).count() + 1;
+                            if (wn < 10)
+                                os << CharT{'0'};
+                            os << wn;
+                        }
+                    }
+#if !ONLY_C_LOCALE
+                    else if (modified == CharT{'O'})
+                    {
+                        const CharT f[] = {'%', modified, *fmt};
+                        tm.tm_year = static_cast<int>(ymd.year()) - 1900;
+                        tm.tm_wday = static_cast<int>(extract_weekday(os, fds));
+                        if (os.fail())
+                            return os;
+                        tm.tm_yday = static_cast<int>((ld - local_days(ymd.year()/1/1)).count());
+                        facet.put(os, os, os.fill(), &tm, std::begin(f), std::end(f));
+                    }
+#endif
+                }
+                modified = CharT{};
+                command = nullptr;
+            }
+            else
+                os << *fmt;
+            break;
+        case 'X':
+            if (command)
+            {
+                if (modified == CharT{'O'})
+                    os << CharT{'%'} << modified << *fmt;
+                else
+                {
+                    if (!fds.has_tod)
+                        os.setstate(std::ios::failbit);
+#if !ONLY_C_LOCALE
+                    tm = std::tm{};
+                    tm.tm_sec = static_cast<int>(fds.tod.seconds().count());
+                    tm.tm_min = static_cast<int>(fds.tod.minutes().count());
+                    tm.tm_hour = static_cast<int>(fds.tod.hours().count());
+                    CharT f[3] = {'%'};
+                    auto fe = std::begin(f) + 1;
+                    if (modified == CharT{'E'})
+                        *fe++ = modified;
+                    *fe++ = *fmt;
+                    facet.put(os, os, os.fill(), &tm, std::begin(f), fe);
+#else
+                    os << fds.tod;
+#endif
+                }
+                command = nullptr;
+                modified = CharT{};
+            }
+            else
+                os << *fmt;
+            break;
+        case 'y':
+            if (command)
+            {
+                if (!fds.ymd.year().ok())
+                    os.setstate(std::ios::failbit);
+                auto y = static_cast<int>(fds.ymd.year());
+#if !ONLY_C_LOCALE
+                if (modified == CharT{})
+                {
+#endif
+                    y = std::abs(y) % 100;
+                    if (y < 10)
+                        os << CharT{'0'};
+                    os << y;
+#if !ONLY_C_LOCALE
+                }
+                else
+                {
+                    const CharT f[] = {'%', modified, *fmt};
+                    tm.tm_year = y - 1900;
+                    facet.put(os, os, os.fill(), &tm, std::begin(f), std::end(f));
+                }
+#endif
+                modified = CharT{};
+                command = nullptr;
+            }
+            else
+                os << *fmt;
+            break;
+        case 'Y':
+            if (command)
+            {
+                if (modified == CharT{'O'})
+                    os << CharT{'%'} << modified << *fmt;
+                else
+                {
+                    if (!fds.ymd.year().ok())
+                        os.setstate(std::ios::failbit);
+                    auto y = fds.ymd.year();
+#if !ONLY_C_LOCALE
+                    if (modified == CharT{})
+#endif
+                    {
+                        save_ostream<CharT, Traits> _(os);
+                        os.imbue(std::locale::classic());
+                        os << y;
+                    }
+#if !ONLY_C_LOCALE
+                    else if (modified == CharT{'E'})
+                    {
+                        const CharT f[] = {'%', modified, *fmt};
+                        tm.tm_year = static_cast<int>(y) - 1900;
+                        facet.put(os, os, os.fill(), &tm, std::begin(f), std::end(f));
+                    }
+#endif
+                }
+                modified = CharT{};
+                command = nullptr;
+            }
+            else
+                os << *fmt;
+            break;
+        case 'z':
+            if (command)
+            {
+                if (offset_sec == nullptr)
+                {
+                    // Can not format %z with unknown offset
+                    os.setstate(ios::failbit);
+                    return os;
+                }
+                auto m = duration_cast<minutes>(*offset_sec);
+                auto neg = m < minutes{0};
+                m = date::abs(m);
+                auto h = duration_cast<hours>(m);
+                m -= h;
+                if (neg)
+                    os << CharT{'-'};
+                else
+                    os << CharT{'+'};
+                if (h < hours{10})
+                    os << CharT{'0'};
+                os << h.count();
+                if (modified != CharT{})
+                    os << CharT{':'};
+                if (m < minutes{10})
+                    os << CharT{'0'};
+                os << m.count();
+                command = nullptr;
+                modified = CharT{};
+            }
+            else
+                os << *fmt;
+            break;
+        case 'Z':
+            if (command)
+            {
+                if (modified == CharT{})
+                {
+                    if (abbrev == nullptr)
+                    {
+                        // Can not format %Z with unknown time_zone
+                        os.setstate(ios::failbit);
+                        return os;
+                    }
+                    for (auto c : *abbrev)
+                        os << CharT(c);
+                }
+                else
+                {
+                    os << CharT{'%'} << modified << *fmt;
+                    modified = CharT{};
+                }
+                command = nullptr;
+            }
+            else
+                os << *fmt;
+            break;
+        case 'E':
+        case 'O':
+            if (command)
+            {
+                if (modified == CharT{})
+                {
+                    modified = *fmt;
+                }
+                else
+                {
+                    os << CharT{'%'} << modified << *fmt;
+                    command = nullptr;
+                    modified = CharT{};
+                }
+            }
+            else
+                os << *fmt;
+            break;
+        case '%':
+            if (command)
+            {
+                if (modified == CharT{})
+                {
+                    os << CharT{'%'};
+                    command = nullptr;
+                }
+                else
+                {
+                    os << CharT{'%'} << modified << CharT{'%'};
+                    command = nullptr;
+                    modified = CharT{};
+                }
+            }
+            else
+                command = fmt;
+            break;
+        default:
+            if (command)
+            {
+                os << CharT{'%'};
+                command = nullptr;
+            }
+            if (modified != CharT{})
+            {
+                os << modified;
+                modified = CharT{};
+            }
+            os << *fmt;
+            break;
+        }
+    }
+    if (command)
+        os << CharT{'%'};
+    if (modified != CharT{})
+        os << modified;
+    return os;
+}
+
+template <class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+to_stream(std::basic_ostream<CharT, Traits>& os, const CharT* fmt, const year& y)
+{
+    using CT = std::chrono::seconds;
+    fields<CT> fds{y/0/0};
+    return to_stream(os, fmt, fds);
+}
+
+template <class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+to_stream(std::basic_ostream<CharT, Traits>& os, const CharT* fmt, const month& m)
+{
+    using CT = std::chrono::seconds;
+    fields<CT> fds{m/0/nanyear};
+    return to_stream(os, fmt, fds);
+}
+
+template <class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+to_stream(std::basic_ostream<CharT, Traits>& os, const CharT* fmt, const day& d)
+{
+    using CT = std::chrono::seconds;
+    fields<CT> fds{d/0/nanyear};
+    return to_stream(os, fmt, fds);
+}
+
+template <class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+to_stream(std::basic_ostream<CharT, Traits>& os, const CharT* fmt, const weekday& wd)
+{
+    using CT = std::chrono::seconds;
+    fields<CT> fds{wd};
+    return to_stream(os, fmt, fds);
+}
+
+template <class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+to_stream(std::basic_ostream<CharT, Traits>& os, const CharT* fmt, const year_month& ym)
+{
+    using CT = std::chrono::seconds;
+    fields<CT> fds{ym/0};
+    return to_stream(os, fmt, fds);
+}
+
+template <class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+to_stream(std::basic_ostream<CharT, Traits>& os, const CharT* fmt, const month_day& md)
+{
+    using CT = std::chrono::seconds;
+    fields<CT> fds{md/nanyear};
+    return to_stream(os, fmt, fds);
+}
+
+template <class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+to_stream(std::basic_ostream<CharT, Traits>& os, const CharT* fmt,
+          const year_month_day& ymd)
+{
+    using CT = std::chrono::seconds;
+    fields<CT> fds{ymd};
+    return to_stream(os, fmt, fds);
+}
+
+template <class CharT, class Traits, class Rep, class Period>
+inline
+std::basic_ostream<CharT, Traits>&
+to_stream(std::basic_ostream<CharT, Traits>& os, const CharT* fmt,
+          const std::chrono::duration<Rep, Period>& d)
+{
+    using Duration = std::chrono::duration<Rep, Period>;
+    using CT = typename std::common_type<Duration, std::chrono::seconds>::type;
+    fields<CT> fds{hh_mm_ss<CT>{d}};
+    return to_stream(os, fmt, fds);
+}
+
+template <class CharT, class Traits, class Duration>
+std::basic_ostream<CharT, Traits>&
+to_stream(std::basic_ostream<CharT, Traits>& os, const CharT* fmt,
+          const local_time<Duration>& tp, const std::string* abbrev = nullptr,
+          const std::chrono::seconds* offset_sec = nullptr)
+{
+    using CT = typename std::common_type<Duration, std::chrono::seconds>::type;
+    auto ld = floor<days>(tp);
+    fields<CT> fds{year_month_day{ld}, hh_mm_ss<CT>{tp-local_seconds{ld}}};
+    return to_stream(os, fmt, fds, abbrev, offset_sec);
+}
+
+template <class CharT, class Traits, class Duration>
+std::basic_ostream<CharT, Traits>&
+to_stream(std::basic_ostream<CharT, Traits>& os, const CharT* fmt,
+          const sys_time<Duration>& tp)
+{
+    using std::chrono::seconds;
+    using CT = typename std::common_type<Duration, seconds>::type;
+    const std::string abbrev("UTC");
+    CONSTDATA seconds offset{0};
+    auto sd = floor<days>(tp);
+    fields<CT> fds{year_month_day{sd}, hh_mm_ss<CT>{tp-sys_seconds{sd}}};
+    return to_stream(os, fmt, fds, &abbrev, &offset);
+}
+
+// format
+
+template <class CharT, class Streamable>
+auto
+format(const std::locale& loc, const CharT* fmt, const Streamable& tp)
+    -> decltype(to_stream(std::declval<std::basic_ostream<CharT>&>(), fmt, tp),
+                std::basic_string<CharT>{})
+{
+    std::basic_ostringstream<CharT> os;
+    os.exceptions(std::ios::failbit | std::ios::badbit);
+    os.imbue(loc);
+    to_stream(os, fmt, tp);
+    return os.str();
+}
+
+template <class CharT, class Streamable>
+auto
+format(const CharT* fmt, const Streamable& tp)
+    -> decltype(to_stream(std::declval<std::basic_ostream<CharT>&>(), fmt, tp),
+                std::basic_string<CharT>{})
+{
+    std::basic_ostringstream<CharT> os;
+    os.exceptions(std::ios::failbit | std::ios::badbit);
+    to_stream(os, fmt, tp);
+    return os.str();
+}
+
+template <class CharT, class Traits, class Alloc, class Streamable>
+auto
+format(const std::locale& loc, const std::basic_string<CharT, Traits, Alloc>& fmt,
+       const Streamable& tp)
+    -> decltype(to_stream(std::declval<std::basic_ostream<CharT, Traits>&>(), fmt.c_str(), tp),
+                std::basic_string<CharT, Traits, Alloc>{})
+{
+    std::basic_ostringstream<CharT, Traits, Alloc> os;
+    os.exceptions(std::ios::failbit | std::ios::badbit);
+    os.imbue(loc);
+    to_stream(os, fmt.c_str(), tp);
+    return os.str();
+}
+
+template <class CharT, class Traits, class Alloc, class Streamable>
+auto
+format(const std::basic_string<CharT, Traits, Alloc>& fmt, const Streamable& tp)
+    -> decltype(to_stream(std::declval<std::basic_ostream<CharT, Traits>&>(), fmt.c_str(), tp),
+                std::basic_string<CharT, Traits, Alloc>{})
+{
+    std::basic_ostringstream<CharT, Traits, Alloc> os;
+    os.exceptions(std::ios::failbit | std::ios::badbit);
+    to_stream(os, fmt.c_str(), tp);
+    return os.str();
+}
+
+// parse
+
+namespace detail
+{
+
+template <class CharT, class Traits>
+bool
+read_char(std::basic_istream<CharT, Traits>& is, CharT fmt, std::ios::iostate& err)
+{
+    auto ic = is.get();
+    if (Traits::eq_int_type(ic, Traits::eof()) ||
+       !Traits::eq(Traits::to_char_type(ic), fmt))
+    {
+        err |= std::ios::failbit;
+        is.setstate(std::ios::failbit);
+        return false;
+    }
+    return true;
+}
+
+template <class CharT, class Traits>
+unsigned
+read_unsigned(std::basic_istream<CharT, Traits>& is, unsigned m = 1, unsigned M = 10)
+{
+    unsigned x = 0;
+    unsigned count = 0;
+    while (true)
+    {
+        auto ic = is.peek();
+        if (Traits::eq_int_type(ic, Traits::eof()))
+            break;
+        auto c = static_cast<char>(Traits::to_char_type(ic));
+        if (!('0' <= c && c <= '9'))
+            break;
+        (void)is.get();
+        ++count;
+        x = 10*x + static_cast<unsigned>(c - '0');
+        if (count == M)
+            break;
+    }
+    if (count < m)
+        is.setstate(std::ios::failbit);
+    return x;
+}
+
+template <class CharT, class Traits>
+int
+read_signed(std::basic_istream<CharT, Traits>& is, unsigned m = 1, unsigned M = 10)
+{
+    auto ic = is.peek();
+    if (!Traits::eq_int_type(ic, Traits::eof()))
+    {
+        auto c = static_cast<char>(Traits::to_char_type(ic));
+        if (('0' <= c && c <= '9') || c == '-' || c == '+')
+        {
+            if (c == '-' || c == '+')
+                (void)is.get();
+            auto x = static_cast<int>(read_unsigned(is, std::max(m, 1u), M));
+            if (!is.fail())
+            {
+                if (c == '-')
+                    x = -x;
+                return x;
+            }
+        }
+    }
+    if (m > 0)
+        is.setstate(std::ios::failbit);
+    return 0;
+}
+
+template <class CharT, class Traits>
+long double
+read_long_double(std::basic_istream<CharT, Traits>& is, unsigned m = 1, unsigned M = 10)
+{
+    unsigned count = 0;
+    unsigned fcount = 0;
+    unsigned long long i = 0;
+    unsigned long long f = 0;
+    bool parsing_fraction = false;
+#if ONLY_C_LOCALE
+    typename Traits::int_type decimal_point = '.';
+#else
+    auto decimal_point = Traits::to_int_type(
+        std::use_facet<std::numpunct<CharT>>(is.getloc()).decimal_point());
+#endif
+    while (true)
+    {
+        auto ic = is.peek();
+        if (Traits::eq_int_type(ic, Traits::eof()))
+            break;
+        if (Traits::eq_int_type(ic, decimal_point))
+        {
+            decimal_point = Traits::eof();
+            parsing_fraction = true;
+        }
+        else
+        {
+            auto c = static_cast<char>(Traits::to_char_type(ic));
+            if (!('0' <= c && c <= '9'))
+                break;
+            if (!parsing_fraction)
+            {
+                i = 10*i + static_cast<unsigned>(c - '0');
+            }
+            else
+            {
+                f = 10*f + static_cast<unsigned>(c - '0');
+                ++fcount;
+            }
+        }
+        (void)is.get();
+        if (++count == M)
+            break;
+    }
+    if (count < m)
+    {
+        is.setstate(std::ios::failbit);
+        return 0;
+    }
+    return i + f/std::pow(10.L, fcount);
+}
+
+struct rs
+{
+    int& i;
+    unsigned m;
+    unsigned M;
+};
+
+struct ru
+{
+    int& i;
+    unsigned m;
+    unsigned M;
+};
+
+struct rld
+{
+    long double& i;
+    unsigned m;
+    unsigned M;
+};
+
+template <class CharT, class Traits>
+void
+read(std::basic_istream<CharT, Traits>&)
+{
+}
+
+template <class CharT, class Traits, class ...Args>
+void
+read(std::basic_istream<CharT, Traits>& is, CharT a0, Args&& ...args);
+
+template <class CharT, class Traits, class ...Args>
+void
+read(std::basic_istream<CharT, Traits>& is, rs a0, Args&& ...args);
+
+template <class CharT, class Traits, class ...Args>
+void
+read(std::basic_istream<CharT, Traits>& is, ru a0, Args&& ...args);
+
+template <class CharT, class Traits, class ...Args>
+void
+read(std::basic_istream<CharT, Traits>& is, int a0, Args&& ...args);
+
+template <class CharT, class Traits, class ...Args>
+void
+read(std::basic_istream<CharT, Traits>& is, rld a0, Args&& ...args);
+
+template <class CharT, class Traits, class ...Args>
+void
+read(std::basic_istream<CharT, Traits>& is, CharT a0, Args&& ...args)
+{
+    // No-op if a0 == CharT{}
+    if (a0 != CharT{})
+    {
+        auto ic = is.peek();
+        if (Traits::eq_int_type(ic, Traits::eof()))
+        {
+            is.setstate(std::ios::failbit | std::ios::eofbit);
+            return;
+        }
+        if (!Traits::eq(Traits::to_char_type(ic), a0))
+        {
+            is.setstate(std::ios::failbit);
+            return;
+        }
+        (void)is.get();
+    }
+    read(is, std::forward<Args>(args)...);
+}
+
+template <class CharT, class Traits, class ...Args>
+void
+read(std::basic_istream<CharT, Traits>& is, rs a0, Args&& ...args)
+{
+    auto x = read_signed(is, a0.m, a0.M);
+    if (is.fail())
+        return;
+    a0.i = x;
+    read(is, std::forward<Args>(args)...);
+}
+
+template <class CharT, class Traits, class ...Args>
+void
+read(std::basic_istream<CharT, Traits>& is, ru a0, Args&& ...args)
+{
+    auto x = read_unsigned(is, a0.m, a0.M);
+    if (is.fail())
+        return;
+    a0.i = static_cast<int>(x);
+    read(is, std::forward<Args>(args)...);
+}
+
+template <class CharT, class Traits, class ...Args>
+void
+read(std::basic_istream<CharT, Traits>& is, int a0, Args&& ...args)
+{
+    if (a0 != -1)
+    {
+        auto u = static_cast<unsigned>(a0);
+        CharT buf[std::numeric_limits<unsigned>::digits10+2u] = {};
+        auto e = buf;
+        do
+        {
+            *e++ = static_cast<CharT>(CharT(u % 10) + CharT{'0'});
+            u /= 10;
+        } while (u > 0);
+        std::reverse(buf, e);
+        for (auto p = buf; p != e && is.rdstate() == std::ios::goodbit; ++p)
+            read(is, *p);
+    }
+    if (is.rdstate() == std::ios::goodbit)
+        read(is, std::forward<Args>(args)...);
+}
+
+template <class CharT, class Traits, class ...Args>
+void
+read(std::basic_istream<CharT, Traits>& is, rld a0, Args&& ...args)
+{
+    auto x = read_long_double(is, a0.m, a0.M);
+    if (is.fail())
+        return;
+    a0.i = x;
+    read(is, std::forward<Args>(args)...);
+}
+
+template <class T, class CharT, class Traits>
+inline
+void
+checked_set(T& value, T from, T not_a_value, std::basic_ios<CharT, Traits>& is)
+{
+    if (!is.fail())
+    {
+        if (value == not_a_value)
+            value = std::move(from);
+        else if (value != from)
+            is.setstate(std::ios::failbit);
+    }
+}
+
+}  // namespace detail;
+
+template <class CharT, class Traits, class Duration, class Alloc = std::allocator<CharT>>
+std::basic_istream<CharT, Traits>&
+from_stream(std::basic_istream<CharT, Traits>& is, const CharT* fmt,
+            fields<Duration>& fds, std::basic_string<CharT, Traits, Alloc>* abbrev,
+            std::chrono::minutes* offset)
+{
+    using std::numeric_limits;
+    using std::ios;
+    using std::chrono::duration;
+    using std::chrono::duration_cast;
+    using std::chrono::seconds;
+    using std::chrono::minutes;
+    using std::chrono::hours;
+    using detail::round_i;
+    typename std::basic_istream<CharT, Traits>::sentry ok{is, true};
+    if (ok)
+    {
+        date::detail::save_istream<CharT, Traits> ss(is);
+        is.fill(' ');
+        is.flags(std::ios::skipws | std::ios::dec);
+        is.width(0);
+#if !ONLY_C_LOCALE
+        auto& f = std::use_facet<std::time_get<CharT>>(is.getloc());
+        std::tm tm{};
+#endif
+        const CharT* command = nullptr;
+        auto modified = CharT{};
+        auto width = -1;
+
+        CONSTDATA int not_a_year = numeric_limits<short>::min();
+        CONSTDATA int not_a_2digit_year = 100;
+        CONSTDATA int not_a_century = not_a_year / 100;
+        CONSTDATA int not_a_month = 0;
+        CONSTDATA int not_a_day = 0;
+        CONSTDATA int not_a_hour = numeric_limits<int>::min();
+        CONSTDATA int not_a_hour_12_value = 0;
+        CONSTDATA int not_a_minute = not_a_hour;
+        CONSTDATA Duration not_a_second = Duration::min();
+        CONSTDATA int not_a_doy = -1;
+        CONSTDATA int not_a_weekday = 8;
+        CONSTDATA int not_a_week_num = 100;
+        CONSTDATA int not_a_ampm = -1;
+        CONSTDATA minutes not_a_offset = minutes::min();
+
+        int Y = not_a_year;             // c, F, Y                   *
+        int y = not_a_2digit_year;      // D, x, y                   *
+        int g = not_a_2digit_year;      // g                         *
+        int G = not_a_year;             // G                         *
+        int C = not_a_century;          // C                         *
+        int m = not_a_month;            // b, B, h, m, c, D, F, x    *
+        int d = not_a_day;              // c, d, D, e, F, x          *
+        int j = not_a_doy;              // j                         *
+        int wd = not_a_weekday;         // a, A, u, w                *
+        int H = not_a_hour;             // c, H, R, T, X             *
+        int I = not_a_hour_12_value;    // I, r                      *
+        int p = not_a_ampm;             // p, r                      *
+        int M = not_a_minute;           // c, M, r, R, T, X          *
+        Duration s = not_a_second;      // c, r, S, T, X             *
+        int U = not_a_week_num;         // U                         *
+        int V = not_a_week_num;         // V                         *
+        int W = not_a_week_num;         // W                         *
+        std::basic_string<CharT, Traits, Alloc> temp_abbrev;  // Z   *
+        minutes temp_offset = not_a_offset;  // z                    *
+
+        using detail::read;
+        using detail::rs;
+        using detail::ru;
+        using detail::rld;
+        using detail::checked_set;
+        for (; *fmt != CharT{} && !is.fail(); ++fmt)
+        {
+            switch (*fmt)
+            {
+            case 'a':
+            case 'A':
+            case 'u':
+            case 'w':  // wd:  a, A, u, w
+                if (command)
+                {
+                    int trial_wd = not_a_weekday;
+                    if (*fmt == 'a' || *fmt == 'A')
+                    {
+                        if (modified == CharT{})
+                        {
+#if !ONLY_C_LOCALE
+                            ios::iostate err = ios::goodbit;
+                            f.get(is, nullptr, is, err, &tm, command, fmt+1);
+                            is.setstate(err);
+                            if (!is.fail())
+                                trial_wd = tm.tm_wday;
+#else
+                            auto nm = detail::weekday_names();
+                            auto i = detail::scan_keyword(is, nm.first, nm.second) - nm.first;
+                            if (!is.fail())
+                                trial_wd = i % 7;
+#endif
+                        }
+                        else
+                            read(is, CharT{'%'}, width, modified, *fmt);
+                    }
+                    else  // *fmt == 'u' || *fmt == 'w'
+                    {
+#if !ONLY_C_LOCALE
+                        if (modified == CharT{})
+#else
+                        if (modified != CharT{'E'})
+#endif
+                        {
+                            read(is, ru{trial_wd, 1, width == -1 ?
+                                                      1u : static_cast<unsigned>(width)});
+                            if (!is.fail())
+                            {
+                                if (*fmt == 'u')
+                                {
+                                    if (!(1 <= trial_wd && trial_wd <= 7))
+                                    {
+                                        trial_wd = not_a_weekday;
+                                        is.setstate(ios::failbit);
+                                    }
+                                    else if (trial_wd == 7)
+                                        trial_wd = 0;
+                                }
+                                else  // *fmt == 'w'
+                                {
+                                    if (!(0 <= trial_wd && trial_wd <= 6))
+                                    {
+                                        trial_wd = not_a_weekday;
+                                        is.setstate(ios::failbit);
+                                    }
+                                }
+                            }
+                        }
+#if !ONLY_C_LOCALE
+                        else if (modified == CharT{'O'})
+                        {
+                            ios::iostate err = ios::goodbit;
+                            f.get(is, nullptr, is, err, &tm, command, fmt+1);
+                            is.setstate(err);
+                            if (!is.fail())
+                                trial_wd = tm.tm_wday;
+                        }
+#endif
+                        else
+                            read(is, CharT{'%'}, width, modified, *fmt);
+                    }
+                    if (trial_wd != not_a_weekday)
+                        checked_set(wd, trial_wd, not_a_weekday, is);
+                }
+                else  // !command
+                    read(is, *fmt);
+                command = nullptr;
+                width = -1;
+                modified = CharT{};
+                break;
+            case 'b':
+            case 'B':
+            case 'h':
+                if (command)
+                {
+                    if (modified == CharT{})
+                    {
+                        int ttm = not_a_month;
+#if !ONLY_C_LOCALE
+                        ios::iostate err = ios::goodbit;
+                        f.get(is, nullptr, is, err, &tm, command, fmt+1);
+                        if ((err & ios::failbit) == 0)
+                            ttm = tm.tm_mon + 1;
+                        is.setstate(err);
+#else
+                        auto nm = detail::month_names();
+                        auto i = detail::scan_keyword(is, nm.first, nm.second) - nm.first;
+                        if (!is.fail())
+                            ttm = i % 12 + 1;
+#endif
+                        checked_set(m, ttm, not_a_month, is);
+                    }
+                    else
+                        read(is, CharT{'%'}, width, modified, *fmt);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+                break;
+            case 'c':
+                if (command)
+                {
+                    if (modified != CharT{'O'})
+                    {
+#if !ONLY_C_LOCALE
+                        ios::iostate err = ios::goodbit;
+                        f.get(is, nullptr, is, err, &tm, command, fmt+1);
+                        if ((err & ios::failbit) == 0)
+                        {
+                            checked_set(Y, tm.tm_year + 1900, not_a_year, is);
+                            checked_set(m, tm.tm_mon + 1, not_a_month, is);
+                            checked_set(d, tm.tm_mday, not_a_day, is);
+                            checked_set(H, tm.tm_hour, not_a_hour, is);
+                            checked_set(M, tm.tm_min, not_a_minute, is);
+                            checked_set(s, duration_cast<Duration>(seconds{tm.tm_sec}),
+                                        not_a_second, is);
+                        }
+                        is.setstate(err);
+#else
+                        // "%a %b %e %T %Y"
+                        auto nm = detail::weekday_names();
+                        auto i = detail::scan_keyword(is, nm.first, nm.second) - nm.first;
+                        checked_set(wd, static_cast<int>(i % 7), not_a_weekday, is);
+                        ws(is);
+                        nm = detail::month_names();
+                        i = detail::scan_keyword(is, nm.first, nm.second) - nm.first;
+                        checked_set(m, static_cast<int>(i % 12 + 1), not_a_month, is);
+                        ws(is);
+                        int td = not_a_day;
+                        read(is, rs{td, 1, 2});
+                        checked_set(d, td, not_a_day, is);
+                        ws(is);
+                        using dfs = detail::decimal_format_seconds<Duration>;
+                        CONSTDATA auto w = Duration::period::den == 1 ? 2 : 3 + dfs::width;
+                        int tH;
+                        int tM;
+                        long double S;
+                        read(is, ru{tH, 1, 2}, CharT{':'}, ru{tM, 1, 2},
+                                               CharT{':'}, rld{S, 1, w});
+                        checked_set(H, tH, not_a_hour, is);
+                        checked_set(M, tM, not_a_minute, is);
+                        checked_set(s, round_i<Duration>(duration<long double>{S}),
+                                    not_a_second, is);
+                        ws(is);
+                        int tY = not_a_year;
+                        read(is, rs{tY, 1, 4u});
+                        checked_set(Y, tY, not_a_year, is);
+#endif
+                    }
+                    else
+                        read(is, CharT{'%'}, width, modified, *fmt);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+                break;
+            case 'x':
+                if (command)
+                {
+                    if (modified != CharT{'O'})
+                    {
+#if !ONLY_C_LOCALE
+                        ios::iostate err = ios::goodbit;
+                        f.get(is, nullptr, is, err, &tm, command, fmt+1);
+                        if ((err & ios::failbit) == 0)
+                        {
+                            checked_set(Y, tm.tm_year + 1900, not_a_year, is);
+                            checked_set(m, tm.tm_mon + 1, not_a_month, is);
+                            checked_set(d, tm.tm_mday, not_a_day, is);
+                        }
+                        is.setstate(err);
+#else
+                        // "%m/%d/%y"
+                        int ty = not_a_2digit_year;
+                        int tm = not_a_month;
+                        int td = not_a_day;
+                        read(is, ru{tm, 1, 2}, CharT{'/'}, ru{td, 1, 2}, CharT{'/'},
+                                 rs{ty, 1, 2});
+                        checked_set(y, ty, not_a_2digit_year, is);
+                        checked_set(m, tm, not_a_month, is);
+                        checked_set(d, td, not_a_day, is);
+#endif
+                    }
+                    else
+                        read(is, CharT{'%'}, width, modified, *fmt);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+                break;
+            case 'X':
+                if (command)
+                {
+                    if (modified != CharT{'O'})
+                    {
+#if !ONLY_C_LOCALE
+                        ios::iostate err = ios::goodbit;
+                        f.get(is, nullptr, is, err, &tm, command, fmt+1);
+                        if ((err & ios::failbit) == 0)
+                        {
+                            checked_set(H, tm.tm_hour, not_a_hour, is);
+                            checked_set(M, tm.tm_min, not_a_minute, is);
+                            checked_set(s, duration_cast<Duration>(seconds{tm.tm_sec}),
+                                        not_a_second, is);
+                        }
+                        is.setstate(err);
+#else
+                        // "%T"
+                        using dfs = detail::decimal_format_seconds<Duration>;
+                        CONSTDATA auto w = Duration::period::den == 1 ? 2 : 3 + dfs::width;
+                        int tH = not_a_hour;
+                        int tM = not_a_minute;
+                        long double S;
+                        read(is, ru{tH, 1, 2}, CharT{':'}, ru{tM, 1, 2},
+                                               CharT{':'}, rld{S, 1, w});
+                        checked_set(H, tH, not_a_hour, is);
+                        checked_set(M, tM, not_a_minute, is);
+                        checked_set(s, round_i<Duration>(duration<long double>{S}),
+                                    not_a_second, is);
+#endif
+                    }
+                    else
+                        read(is, CharT{'%'}, width, modified, *fmt);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+                break;
+            case 'C':
+                if (command)
+                {
+                    int tC = not_a_century;
+#if !ONLY_C_LOCALE
+                    if (modified == CharT{})
+                    {
+#endif
+                        read(is, rs{tC, 1, width == -1 ? 2u : static_cast<unsigned>(width)});
+#if !ONLY_C_LOCALE
+                    }
+                    else
+                    {
+                        ios::iostate err = ios::goodbit;
+                        f.get(is, nullptr, is, err, &tm, command, fmt+1);
+                        if ((err & ios::failbit) == 0)
+                        {
+                            auto tY = tm.tm_year + 1900;
+                            tC = (tY >= 0 ? tY : tY-99) / 100;
+                        }
+                        is.setstate(err);
+                    }
+#endif
+                    checked_set(C, tC, not_a_century, is);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+                break;
+            case 'D':
+                if (command)
+                {
+                    if (modified == CharT{})
+                    {
+                        int tn = not_a_month;
+                        int td = not_a_day;
+                        int ty = not_a_2digit_year;
+                        read(is, ru{tn, 1, 2}, CharT{'\0'}, CharT{'/'}, CharT{'\0'},
+                                 ru{td, 1, 2}, CharT{'\0'}, CharT{'/'}, CharT{'\0'},
+                                 rs{ty, 1, 2});
+                        checked_set(y, ty, not_a_2digit_year, is);
+                        checked_set(m, tn, not_a_month, is);
+                        checked_set(d, td, not_a_day, is);
+                    }
+                    else
+                        read(is, CharT{'%'}, width, modified, *fmt);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+                break;
+            case 'F':
+                if (command)
+                {
+                    if (modified == CharT{})
+                    {
+                        int tY = not_a_year;
+                        int tn = not_a_month;
+                        int td = not_a_day;
+                        read(is, rs{tY, 1, width == -1 ? 4u : static_cast<unsigned>(width)},
+                                 CharT{'-'}, ru{tn, 1, 2}, CharT{'-'}, ru{td, 1, 2});
+                        checked_set(Y, tY, not_a_year, is);
+                        checked_set(m, tn, not_a_month, is);
+                        checked_set(d, td, not_a_day, is);
+                    }
+                    else
+                        read(is, CharT{'%'}, width, modified, *fmt);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+                break;
+            case 'd':
+            case 'e':
+                if (command)
+                {
+#if !ONLY_C_LOCALE
+                    if (modified == CharT{})
+#else
+                    if (modified != CharT{'E'})
+#endif
+                    {
+                        int td = not_a_day;
+                        read(is, rs{td, 1, width == -1 ? 2u : static_cast<unsigned>(width)});
+                        checked_set(d, td, not_a_day, is);
+                    }
+#if !ONLY_C_LOCALE
+                    else if (modified == CharT{'O'})
+                    {
+                        ios::iostate err = ios::goodbit;
+                        f.get(is, nullptr, is, err, &tm, command, fmt+1);
+                        command = nullptr;
+                        width = -1;
+                        modified = CharT{};
+                        if ((err & ios::failbit) == 0)
+                            checked_set(d, tm.tm_mday, not_a_day, is);
+                        is.setstate(err);
+                    }
+#endif
+                    else
+                        read(is, CharT{'%'}, width, modified, *fmt);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+                break;
+            case 'H':
+                if (command)
+                {
+#if !ONLY_C_LOCALE
+                    if (modified == CharT{})
+#else
+                    if (modified != CharT{'E'})
+#endif
+                    {
+                        int tH = not_a_hour;
+                        read(is, ru{tH, 1, width == -1 ? 2u : static_cast<unsigned>(width)});
+                        checked_set(H, tH, not_a_hour, is);
+                    }
+#if !ONLY_C_LOCALE
+                    else if (modified == CharT{'O'})
+                    {
+                        ios::iostate err = ios::goodbit;
+                        f.get(is, nullptr, is, err, &tm, command, fmt+1);
+                        if ((err & ios::failbit) == 0)
+                            checked_set(H, tm.tm_hour, not_a_hour, is);
+                        is.setstate(err);
+                    }
+#endif
+                    else
+                        read(is, CharT{'%'}, width, modified, *fmt);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+                break;
+            case 'I':
+                if (command)
+                {
+                    if (modified == CharT{})
+                    {
+                        int tI = not_a_hour_12_value;
+                        // reads in an hour into I, but most be in [1, 12]
+                        read(is, rs{tI, 1, width == -1 ? 2u : static_cast<unsigned>(width)});
+                        if (!(1 <= tI && tI <= 12))
+                            is.setstate(ios::failbit);
+                        checked_set(I, tI, not_a_hour_12_value, is);
+                    }
+                    else
+                        read(is, CharT{'%'}, width, modified, *fmt);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+               break;
+            case 'j':
+                if (command)
+                {
+                    if (modified == CharT{})
+                    {
+                        int tj = not_a_doy;
+                        read(is, ru{tj, 1, width == -1 ? 3u : static_cast<unsigned>(width)});
+                        checked_set(j, tj, not_a_doy, is);
+                    }
+                    else
+                        read(is, CharT{'%'}, width, modified, *fmt);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+                break;
+            case 'M':
+                if (command)
+                {
+#if !ONLY_C_LOCALE
+                    if (modified == CharT{})
+#else
+                    if (modified != CharT{'E'})
+#endif
+                    {
+                        int tM = not_a_minute;
+                        read(is, ru{tM, 1, width == -1 ? 2u : static_cast<unsigned>(width)});
+                        checked_set(M, tM, not_a_minute, is);
+                    }
+#if !ONLY_C_LOCALE
+                    else if (modified == CharT{'O'})
+                    {
+                        ios::iostate err = ios::goodbit;
+                        f.get(is, nullptr, is, err, &tm, command, fmt+1);
+                        if ((err & ios::failbit) == 0)
+                            checked_set(M, tm.tm_min, not_a_minute, is);
+                        is.setstate(err);
+                    }
+#endif
+                    else
+                        read(is, CharT{'%'}, width, modified, *fmt);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+                break;
+            case 'm':
+                if (command)
+                {
+#if !ONLY_C_LOCALE
+                    if (modified == CharT{})
+#else
+                    if (modified != CharT{'E'})
+#endif
+                    {
+                        int tn = not_a_month;
+                        read(is, rs{tn, 1, width == -1 ? 2u : static_cast<unsigned>(width)});
+                        checked_set(m, tn, not_a_month, is);
+                    }
+#if !ONLY_C_LOCALE
+                    else if (modified == CharT{'O'})
+                    {
+                        ios::iostate err = ios::goodbit;
+                        f.get(is, nullptr, is, err, &tm, command, fmt+1);
+                        if ((err & ios::failbit) == 0)
+                            checked_set(m, tm.tm_mon + 1, not_a_month, is);
+                        is.setstate(err);
+                    }
+#endif
+                    else
+                        read(is, CharT{'%'}, width, modified, *fmt);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+                break;
+            case 'n':
+            case 't':
+                if (command)
+                {
+                    if (modified == CharT{})
+                    {
+                        // %n matches a single white space character
+                        // %t matches 0 or 1 white space characters
+                        auto ic = is.peek();
+                        if (Traits::eq_int_type(ic, Traits::eof()))
+                        {
+                            ios::iostate err = ios::eofbit;
+                            if (*fmt == 'n')
+                                err |= ios::failbit;
+                            is.setstate(err);
+                            break;
+                        }
+                        if (isspace(ic))
+                        {
+                            (void)is.get();
+                        }
+                        else if (*fmt == 'n')
+                            is.setstate(ios::failbit);
+                    }
+                    else
+                        read(is, CharT{'%'}, width, modified, *fmt);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+                break;
+            case 'p':
+                if (command)
+                {
+                    if (modified == CharT{})
+                    {
+                        int tp = not_a_ampm;
+#if !ONLY_C_LOCALE
+                        tm = std::tm{};
+                        tm.tm_hour = 1;
+                        ios::iostate err = ios::goodbit;
+                        f.get(is, nullptr, is, err, &tm, command, fmt+1);
+                        is.setstate(err);
+                        if (tm.tm_hour == 1)
+                            tp = 0;
+                        else if (tm.tm_hour == 13)
+                            tp = 1;
+                        else
+                            is.setstate(err);
+#else
+                        auto nm = detail::ampm_names();
+                        auto i = detail::scan_keyword(is, nm.first, nm.second) - nm.first;
+                        tp = static_cast<decltype(tp)>(i);
+#endif
+                        checked_set(p, tp, not_a_ampm, is);
+                    }
+                    else
+                        read(is, CharT{'%'}, width, modified, *fmt);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+
+               break;
+            case 'r':
+                if (command)
+                {
+                    if (modified == CharT{})
+                    {
+#if !ONLY_C_LOCALE
+                        ios::iostate err = ios::goodbit;
+                        f.get(is, nullptr, is, err, &tm, command, fmt+1);
+                        if ((err & ios::failbit) == 0)
+                        {
+                            checked_set(H, tm.tm_hour, not_a_hour, is);
+                            checked_set(M, tm.tm_min, not_a_hour, is);
+                            checked_set(s, duration_cast<Duration>(seconds{tm.tm_sec}),
+                                        not_a_second, is);
+                        }
+                        is.setstate(err);
+#else
+                        // "%I:%M:%S %p"
+                        using dfs = detail::decimal_format_seconds<Duration>;
+                        CONSTDATA auto w = Duration::period::den == 1 ? 2 : 3 + dfs::width;
+                        long double S;
+                        int tI = not_a_hour_12_value;
+                        int tM = not_a_minute;
+                        read(is, ru{tI, 1, 2}, CharT{':'}, ru{tM, 1, 2},
+                                               CharT{':'}, rld{S, 1, w});
+                        checked_set(I, tI, not_a_hour_12_value, is);
+                        checked_set(M, tM, not_a_minute, is);
+                        checked_set(s, round_i<Duration>(duration<long double>{S}),
+                                    not_a_second, is);
+                        ws(is);
+                        auto nm = detail::ampm_names();
+                        auto i = detail::scan_keyword(is, nm.first, nm.second) - nm.first;
+                        checked_set(p, static_cast<int>(i), not_a_ampm, is);
+#endif
+                    }
+                    else
+                        read(is, CharT{'%'}, width, modified, *fmt);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+                break;
+            case 'R':
+                if (command)
+                {
+                    if (modified == CharT{})
+                    {
+                        int tH = not_a_hour;
+                        int tM = not_a_minute;
+                        read(is, ru{tH, 1, 2}, CharT{'\0'}, CharT{':'}, CharT{'\0'},
+                                 ru{tM, 1, 2}, CharT{'\0'});
+                        checked_set(H, tH, not_a_hour, is);
+                        checked_set(M, tM, not_a_minute, is);
+                    }
+                    else
+                        read(is, CharT{'%'}, width, modified, *fmt);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+                break;
+            case 'S':
+                if (command)
+                {
+ #if !ONLY_C_LOCALE
+                   if (modified == CharT{})
+#else
+                   if (modified != CharT{'E'})
+#endif
+                    {
+                        using dfs = detail::decimal_format_seconds<Duration>;
+                        CONSTDATA auto w = Duration::period::den == 1 ? 2 : 3 + dfs::width;
+                        long double S;
+                        read(is, rld{S, 1, width == -1 ? w : static_cast<unsigned>(width)});
+                        checked_set(s, round_i<Duration>(duration<long double>{S}),
+                                    not_a_second, is);
+                    }
+#if !ONLY_C_LOCALE
+                    else if (modified == CharT{'O'})
+                    {
+                        ios::iostate err = ios::goodbit;
+                        f.get(is, nullptr, is, err, &tm, command, fmt+1);
+                        if ((err & ios::failbit) == 0)
+                            checked_set(s, duration_cast<Duration>(seconds{tm.tm_sec}),
+                                        not_a_second, is);
+                        is.setstate(err);
+                    }
+#endif
+                    else
+                        read(is, CharT{'%'}, width, modified, *fmt);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+                break;
+            case 'T':
+                if (command)
+                {
+                    if (modified == CharT{})
+                    {
+                        using dfs = detail::decimal_format_seconds<Duration>;
+                        CONSTDATA auto w = Duration::period::den == 1 ? 2 : 3 + dfs::width;
+                        int tH = not_a_hour;
+                        int tM = not_a_minute;
+                        long double S;
+                        read(is, ru{tH, 1, 2}, CharT{':'}, ru{tM, 1, 2},
+                                               CharT{':'}, rld{S, 1, w});
+                        checked_set(H, tH, not_a_hour, is);
+                        checked_set(M, tM, not_a_minute, is);
+                        checked_set(s, round_i<Duration>(duration<long double>{S}),
+                                    not_a_second, is);
+                    }
+                    else
+                        read(is, CharT{'%'}, width, modified, *fmt);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+                break;
+            case 'Y':
+                if (command)
+                {
+#if !ONLY_C_LOCALE
+                    if (modified == CharT{})
+#else
+                    if (modified != CharT{'O'})
+#endif
+                    {
+                        int tY = not_a_year;
+                        read(is, rs{tY, 1, width == -1 ? 4u : static_cast<unsigned>(width)});
+                        checked_set(Y, tY, not_a_year, is);
+                    }
+#if !ONLY_C_LOCALE
+                    else if (modified == CharT{'E'})
+                    {
+                        ios::iostate err = ios::goodbit;
+                        f.get(is, nullptr, is, err, &tm, command, fmt+1);
+                        if ((err & ios::failbit) == 0)
+                            checked_set(Y, tm.tm_year + 1900, not_a_year, is);
+                        is.setstate(err);
+                    }
+#endif
+                    else
+                        read(is, CharT{'%'}, width, modified, *fmt);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+                break;
+            case 'y':
+                if (command)
+                {
+#if !ONLY_C_LOCALE
+                    if (modified == CharT{})
+#endif
+                    {
+                        int ty = not_a_2digit_year;
+                        read(is, ru{ty, 1, width == -1 ? 2u : static_cast<unsigned>(width)});
+                        checked_set(y, ty, not_a_2digit_year, is);
+                    }
+#if !ONLY_C_LOCALE
+                    else
+                    {
+                        ios::iostate err = ios::goodbit;
+                        f.get(is, nullptr, is, err, &tm, command, fmt+1);
+                        if ((err & ios::failbit) == 0)
+                            checked_set(Y, tm.tm_year + 1900, not_a_year, is);
+                        is.setstate(err);
+                    }
+#endif
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+                break;
+            case 'g':
+                if (command)
+                {
+                    if (modified == CharT{})
+                    {
+                        int tg = not_a_2digit_year;
+                        read(is, ru{tg, 1, width == -1 ? 2u : static_cast<unsigned>(width)});
+                        checked_set(g, tg, not_a_2digit_year, is);
+                    }
+                    else
+                        read(is, CharT{'%'}, width, modified, *fmt);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+                break;
+            case 'G':
+                if (command)
+                {
+                    if (modified == CharT{})
+                    {
+                        int tG = not_a_year;
+                        read(is, rs{tG, 1, width == -1 ? 4u : static_cast<unsigned>(width)});
+                        checked_set(G, tG, not_a_year, is);
+                    }
+                    else
+                        read(is, CharT{'%'}, width, modified, *fmt);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+                break;
+            case 'U':
+                if (command)
+                {
+                    if (modified == CharT{})
+                    {
+                        int tU = not_a_week_num;
+                        read(is, ru{tU, 1, width == -1 ? 2u : static_cast<unsigned>(width)});
+                        checked_set(U, tU, not_a_week_num, is);
+                    }
+                    else
+                        read(is, CharT{'%'}, width, modified, *fmt);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+                break;
+            case 'V':
+                if (command)
+                {
+                    if (modified == CharT{})
+                    {
+                        int tV = not_a_week_num;
+                        read(is, ru{tV, 1, width == -1 ? 2u : static_cast<unsigned>(width)});
+                        checked_set(V, tV, not_a_week_num, is);
+                    }
+                    else
+                        read(is, CharT{'%'}, width, modified, *fmt);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+                break;
+            case 'W':
+                if (command)
+                {
+                    if (modified == CharT{})
+                    {
+                        int tW = not_a_week_num;
+                        read(is, ru{tW, 1, width == -1 ? 2u : static_cast<unsigned>(width)});
+                        checked_set(W, tW, not_a_week_num, is);
+                    }
+                    else
+                        read(is, CharT{'%'}, width, modified, *fmt);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+                break;
+            case 'E':
+            case 'O':
+                if (command)
+                {
+                    if (modified == CharT{})
+                    {
+                        modified = *fmt;
+                    }
+                    else
+                    {
+                        read(is, CharT{'%'}, width, modified, *fmt);
+                        command = nullptr;
+                        width = -1;
+                        modified = CharT{};
+                    }
+                }
+                else
+                    read(is, *fmt);
+                break;
+            case '%':
+                if (command)
+                {
+                    if (modified == CharT{})
+                        read(is, *fmt);
+                    else
+                        read(is, CharT{'%'}, width, modified, *fmt);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    command = fmt;
+                break;
+            case 'z':
+                if (command)
+                {
+                    int tH, tM;
+                    minutes toff = not_a_offset;
+                    bool neg = false;
+                    auto ic = is.peek();
+                    if (!Traits::eq_int_type(ic, Traits::eof()))
+                    {
+                        auto c = static_cast<char>(Traits::to_char_type(ic));
+                        if (c == '-')
+                            neg = true;
+                    }
+                    if (modified == CharT{})
+                    {
+                        read(is, rs{tH, 2, 2});
+                        if (!is.fail())
+                            toff = hours{std::abs(tH)};
+                        if (is.good())
+                        {
+                            ic = is.peek();
+                            if (!Traits::eq_int_type(ic, Traits::eof()))
+                            {
+                                auto c = static_cast<char>(Traits::to_char_type(ic));
+                                if ('0' <= c && c <= '9')
+                                {
+                                    read(is, ru{tM, 2, 2});
+                                    if (!is.fail())
+                                        toff += minutes{tM};
+                                }
+                            }
+                        }
+                    }
+                    else
+                    {
+                        read(is, rs{tH, 1, 2});
+                        if (!is.fail())
+                            toff = hours{std::abs(tH)};
+                        if (is.good())
+                        {
+                            ic = is.peek();
+                            if (!Traits::eq_int_type(ic, Traits::eof()))
+                            {
+                                auto c = static_cast<char>(Traits::to_char_type(ic));
+                                if (c == ':')
+                                {
+                                    (void)is.get();
+                                    read(is, ru{tM, 2, 2});
+                                    if (!is.fail())
+                                        toff += minutes{tM};
+                                }
+                            }
+                        }
+                    }
+                    if (neg)
+                        toff = -toff;
+                    checked_set(temp_offset, toff, not_a_offset, is);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+                break;
+            case 'Z':
+                if (command)
+                {
+                    if (modified == CharT{})
+                    {
+                        std::basic_string<CharT, Traits, Alloc> buf;
+                        while (is.rdstate() == std::ios::goodbit)
+                        {
+                            auto i = is.rdbuf()->sgetc();
+                            if (Traits::eq_int_type(i, Traits::eof()))
+                            {
+                                is.setstate(ios::eofbit);
+                                break;
+                            }
+                            auto wc = Traits::to_char_type(i);
+                            auto c = static_cast<char>(wc);
+                            // is c a valid time zone name or abbreviation character?
+                            if (!(CharT{1} < wc && wc < CharT{127}) || !(isalnum(c) ||
+                                    c == '_' || c == '/' || c == '-' || c == '+'))
+                                break;
+                            buf.push_back(c);
+                            is.rdbuf()->sbumpc();
+                        }
+                        if (buf.empty())
+                            is.setstate(ios::failbit);
+                        checked_set(temp_abbrev, buf, {}, is);
+                    }
+                    else
+                        read(is, CharT{'%'}, width, modified, *fmt);
+                    command = nullptr;
+                    width = -1;
+                    modified = CharT{};
+                }
+                else
+                    read(is, *fmt);
+                break;
+            default:
+                if (command)
+                {
+                    if (width == -1 && modified == CharT{} && '0' <= *fmt && *fmt <= '9')
+                    {
+                        width = static_cast<char>(*fmt) - '0';
+                        while ('0' <= fmt[1] && fmt[1] <= '9')
+                            width = 10*width + static_cast<char>(*++fmt) - '0';
+                    }
+                    else
+                    {
+                        if (modified == CharT{})
+                            read(is, CharT{'%'}, width, *fmt);
+                        else
+                            read(is, CharT{'%'}, width, modified, *fmt);
+                        command = nullptr;
+                        width = -1;
+                        modified = CharT{};
+                    }
+                }
+                else  // !command
+                {
+                    if (isspace(static_cast<unsigned char>(*fmt)))
+                    {
+                        // space matches 0 or more white space characters
+                        if (is.good())
+                           ws(is);
+                    }
+                    else
+                        read(is, *fmt);
+                }
+                break;
+            }
+        }
+        // is.fail() || *fmt == CharT{}
+        if (is.rdstate() == ios::goodbit && command)
+        {
+            if (modified == CharT{})
+                read(is, CharT{'%'}, width);
+            else
+                read(is, CharT{'%'}, width, modified);
+        }
+        if (!is.fail())
+        {
+            if (y != not_a_2digit_year)
+            {
+                // Convert y and an optional C to Y
+                if (!(0 <= y && y <= 99))
+                    goto broken;
+                if (C == not_a_century)
+                {
+                    if (Y == not_a_year)
+                    {
+                        if (y >= 69)
+                            C = 19;
+                        else
+                            C = 20;
+                    }
+                    else
+                    {
+                        C = (Y >= 0 ? Y : Y-100) / 100;
+                    }
+                }
+                int tY;
+                if (C >= 0)
+                    tY = 100*C + y;
+                else
+                    tY = 100*(C+1) - (y == 0 ? 100 : y);
+                if (Y != not_a_year && Y != tY)
+                    goto broken;
+                Y = tY;
+            }
+            if (g != not_a_2digit_year)
+            {
+                // Convert g and an optional C to G
+                if (!(0 <= g && g <= 99))
+                    goto broken;
+                if (C == not_a_century)
+                {
+                    if (G == not_a_year)
+                    {
+                        if (g >= 69)
+                            C = 19;
+                        else
+                            C = 20;
+                    }
+                    else
+                    {
+                        C = (G >= 0 ? G : G-100) / 100;
+                    }
+                }
+                int tG;
+                if (C >= 0)
+                    tG = 100*C + g;
+                else
+                    tG = 100*(C+1) - (g == 0 ? 100 : g);
+                if (G != not_a_year && G != tG)
+                    goto broken;
+                G = tG;
+            }
+            if (Y < static_cast<int>(year::min()) || Y > static_cast<int>(year::max()))
+                Y = not_a_year;
+            bool computed = false;
+            if (G != not_a_year && V != not_a_week_num && wd != not_a_weekday)
+            {
+                year_month_day ymd_trial = sys_days(year{G-1}/December/Thursday[last]) +
+                                           (Monday-Thursday) + weeks{V-1} +
+                                           (weekday{static_cast<unsigned>(wd)}-Monday);
+                if (Y == not_a_year)
+                    Y = static_cast<int>(ymd_trial.year());
+                else if (year{Y} != ymd_trial.year())
+                    goto broken;
+                if (m == not_a_month)
+                    m = static_cast<int>(static_cast<unsigned>(ymd_trial.month()));
+                else if (month(static_cast<unsigned>(m)) != ymd_trial.month())
+                    goto broken;
+                if (d == not_a_day)
+                    d = static_cast<int>(static_cast<unsigned>(ymd_trial.day()));
+                else if (day(static_cast<unsigned>(d)) != ymd_trial.day())
+                    goto broken;
+                computed = true;
+            }
+            if (Y != not_a_year && U != not_a_week_num && wd != not_a_weekday)
+            {
+                year_month_day ymd_trial = sys_days(year{Y}/January/Sunday[1]) +
+                                           weeks{U-1} +
+                                           (weekday{static_cast<unsigned>(wd)} - Sunday);
+                if (Y == not_a_year)
+                    Y = static_cast<int>(ymd_trial.year());
+                else if (year{Y} != ymd_trial.year())
+                    goto broken;
+                if (m == not_a_month)
+                    m = static_cast<int>(static_cast<unsigned>(ymd_trial.month()));
+                else if (month(static_cast<unsigned>(m)) != ymd_trial.month())
+                    goto broken;
+                if (d == not_a_day)
+                    d = static_cast<int>(static_cast<unsigned>(ymd_trial.day()));
+                else if (day(static_cast<unsigned>(d)) != ymd_trial.day())
+                    goto broken;
+                computed = true;
+            }
+            if (Y != not_a_year && W != not_a_week_num && wd != not_a_weekday)
+            {
+                year_month_day ymd_trial = sys_days(year{Y}/January/Monday[1]) +
+                                           weeks{W-1} +
+                                           (weekday{static_cast<unsigned>(wd)} - Monday);
+                if (Y == not_a_year)
+                    Y = static_cast<int>(ymd_trial.year());
+                else if (year{Y} != ymd_trial.year())
+                    goto broken;
+                if (m == not_a_month)
+                    m = static_cast<int>(static_cast<unsigned>(ymd_trial.month()));
+                else if (month(static_cast<unsigned>(m)) != ymd_trial.month())
+                    goto broken;
+                if (d == not_a_day)
+                    d = static_cast<int>(static_cast<unsigned>(ymd_trial.day()));
+                else if (day(static_cast<unsigned>(d)) != ymd_trial.day())
+                    goto broken;
+                computed = true;
+            }
+            if (j != not_a_doy && Y != not_a_year)
+            {
+                auto ymd_trial = year_month_day{local_days(year{Y}/1/1) + days{j-1}};
+                if (m == 0)
+                    m = static_cast<int>(static_cast<unsigned>(ymd_trial.month()));
+                else if (month(static_cast<unsigned>(m)) != ymd_trial.month())
+                    goto broken;
+                if (d == 0)
+                    d = static_cast<int>(static_cast<unsigned>(ymd_trial.day()));
+                else if (day(static_cast<unsigned>(d)) != ymd_trial.day())
+                    goto broken;
+                j = not_a_doy;
+            }
+            auto ymd = year{Y}/m/d;
+            if (ymd.ok())
+            {
+                if (wd == not_a_weekday)
+                    wd = static_cast<int>((weekday(sys_days(ymd)) - Sunday).count());
+                else if (wd != static_cast<int>((weekday(sys_days(ymd)) - Sunday).count()))
+                    goto broken;
+                if (!computed)
+                {
+                    if (G != not_a_year || V != not_a_week_num)
+                    {
+                        sys_days sd = ymd;
+                        auto G_trial = year_month_day{sd + days{3}}.year();
+                        auto start = sys_days((G_trial - years{1})/December/Thursday[last]) +
+                                     (Monday - Thursday);
+                        if (sd < start)
+                        {
+                            --G_trial;
+                            if (V != not_a_week_num)
+                                start = sys_days((G_trial - years{1})/December/Thursday[last])
+                                        + (Monday - Thursday);
+                        }
+                        if (G != not_a_year && G != static_cast<int>(G_trial))
+                            goto broken;
+                        if (V != not_a_week_num)
+                        {
+                            auto V_trial = duration_cast<weeks>(sd - start).count() + 1;
+                            if (V != V_trial)
+                                goto broken;
+                        }
+                    }
+                    if (U != not_a_week_num)
+                    {
+                        auto start = sys_days(Sunday[1]/January/ymd.year());
+                        auto U_trial = floor<weeks>(sys_days(ymd) - start).count() + 1;
+                        if (U != U_trial)
+                            goto broken;
+                    }
+                    if (W != not_a_week_num)
+                    {
+                        auto start = sys_days(Monday[1]/January/ymd.year());
+                        auto W_trial = floor<weeks>(sys_days(ymd) - start).count() + 1;
+                        if (W != W_trial)
+                            goto broken;
+                    }
+                }
+            }
+            fds.ymd = ymd;
+            if (I != not_a_hour_12_value)
+            {
+                if (!(1 <= I && I <= 12))
+                    goto broken;
+                if (p != not_a_ampm)
+                {
+                    // p is in [0, 1] == [AM, PM]
+                    // Store trial H in I
+                    if (I == 12)
+                        --p;
+                    I += p*12;
+                    // Either set H from I or make sure H and I are consistent
+                    if (H == not_a_hour)
+                        H = I;
+                    else if (I != H)
+                        goto broken;
+                }
+                else  // p == not_a_ampm
+                {
+                    // if H, make sure H and I could be consistent
+                    if (H != not_a_hour)
+                    {
+                        if (I == 12)
+                        {
+                            if (H != 0 && H != 12)
+                                goto broken;
+                        }
+                        else if (!(I == H || I == H+12))
+                        {
+                            goto broken;
+                        }
+                    }
+                    else  // I is ambiguous, AM or PM?
+                        goto broken;
+                }
+            }
+            if (H != not_a_hour)
+            {
+                fds.has_tod = true;
+                fds.tod = hh_mm_ss<Duration>{hours{H}};
+            }
+            if (M != not_a_minute)
+            {
+                fds.has_tod = true;
+                fds.tod.m_ = minutes{M};
+            }
+            if (s != not_a_second)
+            {
+                fds.has_tod = true;
+                fds.tod.s_ = detail::decimal_format_seconds<Duration>{s};
+            }
+            if (j != not_a_doy)
+            {
+                fds.has_tod = true;
+                fds.tod.h_ += hours{days{j}};
+            }
+            if (wd != not_a_weekday)
+                fds.wd = weekday{static_cast<unsigned>(wd)};
+            if (abbrev != nullptr)
+                *abbrev = std::move(temp_abbrev);
+            if (offset != nullptr && temp_offset != not_a_offset)
+              *offset = temp_offset;
+        }
+       return is;
+    }
+broken:
+    is.setstate(ios::failbit);
+    return is;
+}
+
+template <class CharT, class Traits, class Alloc = std::allocator<CharT>>
+std::basic_istream<CharT, Traits>&
+from_stream(std::basic_istream<CharT, Traits>& is, const CharT* fmt, year& y,
+            std::basic_string<CharT, Traits, Alloc>* abbrev = nullptr,
+            std::chrono::minutes* offset = nullptr)
+{
+    using CT = std::chrono::seconds;
+    fields<CT> fds{};
+    from_stream(is, fmt, fds, abbrev, offset);
+    if (!fds.ymd.year().ok())
+        is.setstate(std::ios::failbit);
+    if (!is.fail())
+        y = fds.ymd.year();
+    return is;
+}
+
+template <class CharT, class Traits, class Alloc = std::allocator<CharT>>
+std::basic_istream<CharT, Traits>&
+from_stream(std::basic_istream<CharT, Traits>& is, const CharT* fmt, month& m,
+            std::basic_string<CharT, Traits, Alloc>* abbrev = nullptr,
+            std::chrono::minutes* offset = nullptr)
+{
+    using CT = std::chrono::seconds;
+    fields<CT> fds{};
+    from_stream(is, fmt, fds, abbrev, offset);
+    if (!fds.ymd.month().ok())
+        is.setstate(std::ios::failbit);
+    if (!is.fail())
+        m = fds.ymd.month();
+    return is;
+}
+
+template <class CharT, class Traits, class Alloc = std::allocator<CharT>>
+std::basic_istream<CharT, Traits>&
+from_stream(std::basic_istream<CharT, Traits>& is, const CharT* fmt, day& d,
+            std::basic_string<CharT, Traits, Alloc>* abbrev = nullptr,
+            std::chrono::minutes* offset = nullptr)
+{
+    using CT = std::chrono::seconds;
+    fields<CT> fds{};
+    from_stream(is, fmt, fds, abbrev, offset);
+    if (!fds.ymd.day().ok())
+        is.setstate(std::ios::failbit);
+    if (!is.fail())
+        d = fds.ymd.day();
+    return is;
+}
+
+template <class CharT, class Traits, class Alloc = std::allocator<CharT>>
+std::basic_istream<CharT, Traits>&
+from_stream(std::basic_istream<CharT, Traits>& is, const CharT* fmt, weekday& wd,
+            std::basic_string<CharT, Traits, Alloc>* abbrev = nullptr,
+            std::chrono::minutes* offset = nullptr)
+{
+    using CT = std::chrono::seconds;
+    fields<CT> fds{};
+    from_stream(is, fmt, fds, abbrev, offset);
+    if (!fds.wd.ok())
+        is.setstate(std::ios::failbit);
+    if (!is.fail())
+        wd = fds.wd;
+    return is;
+}
+
+template <class CharT, class Traits, class Alloc = std::allocator<CharT>>
+std::basic_istream<CharT, Traits>&
+from_stream(std::basic_istream<CharT, Traits>& is, const CharT* fmt, year_month& ym,
+            std::basic_string<CharT, Traits, Alloc>* abbrev = nullptr,
+            std::chrono::minutes* offset = nullptr)
+{
+    using CT = std::chrono::seconds;
+    fields<CT> fds{};
+    from_stream(is, fmt, fds, abbrev, offset);
+    if (!fds.ymd.month().ok())
+        is.setstate(std::ios::failbit);
+    if (!is.fail())
+        ym = fds.ymd.year()/fds.ymd.month();
+    return is;
+}
+
+template <class CharT, class Traits, class Alloc = std::allocator<CharT>>
+std::basic_istream<CharT, Traits>&
+from_stream(std::basic_istream<CharT, Traits>& is, const CharT* fmt, month_day& md,
+            std::basic_string<CharT, Traits, Alloc>* abbrev = nullptr,
+            std::chrono::minutes* offset = nullptr)
+{
+    using CT = std::chrono::seconds;
+    fields<CT> fds{};
+    from_stream(is, fmt, fds, abbrev, offset);
+    if (!fds.ymd.month().ok() || !fds.ymd.day().ok())
+        is.setstate(std::ios::failbit);
+    if (!is.fail())
+        md = fds.ymd.month()/fds.ymd.day();
+    return is;
+}
+
+template <class CharT, class Traits, class Alloc = std::allocator<CharT>>
+std::basic_istream<CharT, Traits>&
+from_stream(std::basic_istream<CharT, Traits>& is, const CharT* fmt,
+            year_month_day& ymd, std::basic_string<CharT, Traits, Alloc>* abbrev = nullptr,
+            std::chrono::minutes* offset = nullptr)
+{
+    using CT = std::chrono::seconds;
+    fields<CT> fds{};
+    from_stream(is, fmt, fds, abbrev, offset);
+    if (!fds.ymd.ok())
+        is.setstate(std::ios::failbit);
+    if (!is.fail())
+        ymd = fds.ymd;
+    return is;
+}
+
+template <class Duration, class CharT, class Traits, class Alloc = std::allocator<CharT>>
+std::basic_istream<CharT, Traits>&
+from_stream(std::basic_istream<CharT, Traits>& is, const CharT* fmt,
+            sys_time<Duration>& tp, std::basic_string<CharT, Traits, Alloc>* abbrev = nullptr,
+            std::chrono::minutes* offset = nullptr)
+{
+    using CT = typename std::common_type<Duration, std::chrono::seconds>::type;
+    using detail::round_i;
+    std::chrono::minutes offset_local{};
+    auto offptr = offset ? offset : &offset_local;
+    fields<CT> fds{};
+    fds.has_tod = true;
+    from_stream(is, fmt, fds, abbrev, offptr);
+    if (!fds.ymd.ok() || !fds.tod.in_conventional_range())
+        is.setstate(std::ios::failbit);
+    if (!is.fail())
+        tp = round_i<Duration>(sys_days(fds.ymd) - *offptr + fds.tod.to_duration());
+    return is;
+}
+
+template <class Duration, class CharT, class Traits, class Alloc = std::allocator<CharT>>
+std::basic_istream<CharT, Traits>&
+from_stream(std::basic_istream<CharT, Traits>& is, const CharT* fmt,
+            local_time<Duration>& tp, std::basic_string<CharT, Traits, Alloc>* abbrev = nullptr,
+            std::chrono::minutes* offset = nullptr)
+{
+    using CT = typename std::common_type<Duration, std::chrono::seconds>::type;
+    using detail::round_i;
+    fields<CT> fds{};
+    fds.has_tod = true;
+    from_stream(is, fmt, fds, abbrev, offset);
+    if (!fds.ymd.ok() || !fds.tod.in_conventional_range())
+        is.setstate(std::ios::failbit);
+    if (!is.fail())
+        tp = round_i<Duration>(local_seconds{local_days(fds.ymd)} + fds.tod.to_duration());
+    return is;
+}
+
+template <class Rep, class Period, class CharT, class Traits, class Alloc = std::allocator<CharT>>
+std::basic_istream<CharT, Traits>&
+from_stream(std::basic_istream<CharT, Traits>& is, const CharT* fmt,
+            std::chrono::duration<Rep, Period>& d,
+            std::basic_string<CharT, Traits, Alloc>* abbrev = nullptr,
+            std::chrono::minutes* offset = nullptr)
+{
+    using Duration = std::chrono::duration<Rep, Period>;
+    using CT = typename std::common_type<Duration, std::chrono::seconds>::type;
+    fields<CT> fds{};
+    from_stream(is, fmt, fds, abbrev, offset);
+    if (!fds.has_tod)
+        is.setstate(std::ios::failbit);
+    if (!is.fail())
+        d = std::chrono::duration_cast<Duration>(fds.tod.to_duration());
+    return is;
+}
+
+template <class Parsable, class CharT, class Traits = std::char_traits<CharT>,
+          class Alloc = std::allocator<CharT>>
+struct parse_manip
+{
+    const std::basic_string<CharT, Traits, Alloc> format_;
+    Parsable&                                     tp_;
+    std::basic_string<CharT, Traits, Alloc>*      abbrev_;
+    std::chrono::minutes*                         offset_;
+
+public:
+    parse_manip(std::basic_string<CharT, Traits, Alloc> format, Parsable& tp,
+                std::basic_string<CharT, Traits, Alloc>* abbrev = nullptr,
+                std::chrono::minutes* offset = nullptr)
+        : format_(std::move(format))
+        , tp_(tp)
+        , abbrev_(abbrev)
+        , offset_(offset)
+        {}
+
+};
+
+template <class Parsable, class CharT, class Traits, class Alloc>
+std::basic_istream<CharT, Traits>&
+operator>>(std::basic_istream<CharT, Traits>& is,
+           const parse_manip<Parsable, CharT, Traits, Alloc>& x)
+{
+    return from_stream(is, x.format_.c_str(), x.tp_, x.abbrev_, x.offset_);
+}
+
+template <class Parsable, class CharT, class Traits, class Alloc>
+inline
+auto
+parse(const std::basic_string<CharT, Traits, Alloc>& format, Parsable& tp)
+    -> decltype(from_stream(std::declval<std::basic_istream<CharT, Traits>&>(),
+                            format.c_str(), tp),
+                parse_manip<Parsable, CharT, Traits, Alloc>{format, tp})
+{
+    return {format, tp};
+}
+
+template <class Parsable, class CharT, class Traits, class Alloc>
+inline
+auto
+parse(const std::basic_string<CharT, Traits, Alloc>& format, Parsable& tp,
+      std::basic_string<CharT, Traits, Alloc>& abbrev)
+    -> decltype(from_stream(std::declval<std::basic_istream<CharT, Traits>&>(),
+                            format.c_str(), tp, &abbrev),
+                parse_manip<Parsable, CharT, Traits, Alloc>{format, tp, &abbrev})
+{
+    return {format, tp, &abbrev};
+}
+
+template <class Parsable, class CharT, class Traits, class Alloc>
+inline
+auto
+parse(const std::basic_string<CharT, Traits, Alloc>& format, Parsable& tp,
+      std::chrono::minutes& offset)
+    -> decltype(from_stream(std::declval<std::basic_istream<CharT, Traits>&>(),
+                            format.c_str(), tp,
+                            std::declval<std::basic_string<CharT, Traits, Alloc>*>(),
+                            &offset),
+                parse_manip<Parsable, CharT, Traits, Alloc>{format, tp, nullptr, &offset})
+{
+    return {format, tp, nullptr, &offset};
+}
+
+template <class Parsable, class CharT, class Traits, class Alloc>
+inline
+auto
+parse(const std::basic_string<CharT, Traits, Alloc>& format, Parsable& tp,
+      std::basic_string<CharT, Traits, Alloc>& abbrev, std::chrono::minutes& offset)
+    -> decltype(from_stream(std::declval<std::basic_istream<CharT, Traits>&>(),
+                            format.c_str(), tp, &abbrev, &offset),
+                parse_manip<Parsable, CharT, Traits, Alloc>{format, tp, &abbrev, &offset})
+{
+    return {format, tp, &abbrev, &offset};
+}
+
+// const CharT* formats
+
+template <class Parsable, class CharT>
+inline
+auto
+parse(const CharT* format, Parsable& tp)
+    -> decltype(from_stream(std::declval<std::basic_istream<CharT>&>(), format, tp),
+                parse_manip<Parsable, CharT>{format, tp})
+{
+    return {format, tp};
+}
+
+template <class Parsable, class CharT, class Traits, class Alloc>
+inline
+auto
+parse(const CharT* format, Parsable& tp, std::basic_string<CharT, Traits, Alloc>& abbrev)
+    -> decltype(from_stream(std::declval<std::basic_istream<CharT, Traits>&>(), format,
+                            tp, &abbrev),
+                parse_manip<Parsable, CharT, Traits, Alloc>{format, tp, &abbrev})
+{
+    return {format, tp, &abbrev};
+}
+
+template <class Parsable, class CharT>
+inline
+auto
+parse(const CharT* format, Parsable& tp, std::chrono::minutes& offset)
+    -> decltype(from_stream(std::declval<std::basic_istream<CharT>&>(), format,
+                            tp, std::declval<std::basic_string<CharT>*>(), &offset),
+                parse_manip<Parsable, CharT>{format, tp, nullptr, &offset})
+{
+    return {format, tp, nullptr, &offset};
+}
+
+template <class Parsable, class CharT, class Traits, class Alloc>
+inline
+auto
+parse(const CharT* format, Parsable& tp,
+      std::basic_string<CharT, Traits, Alloc>& abbrev, std::chrono::minutes& offset)
+    -> decltype(from_stream(std::declval<std::basic_istream<CharT, Traits>&>(), format,
+                            tp, &abbrev, &offset),
+                parse_manip<Parsable, CharT, Traits, Alloc>{format, tp, &abbrev, &offset})
+{
+    return {format, tp, &abbrev, &offset};
+}
+
+// duration streaming
+
+template <class CharT, class Traits, class Rep, class Period>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os,
+           const std::chrono::duration<Rep, Period>& d)
+{
+    return os << detail::make_string<CharT, Traits>::from(d.count()) +
+                 detail::get_units<CharT>(typename Period::type{});
+}
+
+}  // namespace date
+
+#ifdef _MSC_VER
+#   pragma warning(pop)
+#endif
+
+#ifdef __GNUC__
+# pragma GCC diagnostic pop
+#endif
+
+#endif  // DATE_H
diff --git a/third_party/date-3.0.1/include/date/ios.h b/third_party/date-3.0.1/include/date/ios.h
new file mode 100644
index 00000000..ee54b9d0
--- /dev/null
+++ b/third_party/date-3.0.1/include/date/ios.h
@@ -0,0 +1,50 @@
+//
+//  ios.h
+//  DateTimeLib
+//
+// The MIT License (MIT)
+//
+// Copyright (c) 2016 Alexander Kormanovsky
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+#ifndef ios_hpp
+#define ios_hpp
+
+#if __APPLE__
+# include <TargetConditionals.h>
+# if TARGET_OS_IPHONE
+#   include <string>
+
+    namespace date
+    {
+    namespace iOSUtils
+    {
+    
+    std::string get_tzdata_path();
+    std::string get_current_timezone();
+    
+    }  // namespace iOSUtils
+    }  // namespace date
+
+# endif  // TARGET_OS_IPHONE
+#else   // !__APPLE__
+# define TARGET_OS_IPHONE 0
+#endif  // !__APPLE__
+#endif // ios_hpp
diff --git a/third_party/date-3.0.1/include/date/islamic.h b/third_party/date-3.0.1/include/date/islamic.h
new file mode 100644
index 00000000..82ed6597
--- /dev/null
+++ b/third_party/date-3.0.1/include/date/islamic.h
@@ -0,0 +1,3031 @@
+#ifndef ISLAMIC_H
+#define ISLAMIC_H
+
+// The MIT License (MIT)
+//
+// Copyright (c) 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+//
+// Our apologies.  When the previous paragraph was written, lowercase had not yet
+// been invented (that would involve another several millennia of evolution).
+// We did not mean to shout.
+
+#include "date.h"
+
+namespace islamic
+{
+
+// durations
+
+using days = date::days;
+
+using weeks = date::weeks;
+
+using years = std::chrono::duration
+    <int, date::detail::ratio_multiply<std::ratio<10631, 30>, days::period>>;
+
+using months = std::chrono::duration
+    <int, date::detail::ratio_divide<years::period, std::ratio<12>>>;
+
+// time_point
+
+using sys_days   = date::sys_days;
+using local_days = date::local_days;
+
+// types
+
+struct last_spec
+{
+    explicit last_spec() = default;
+};
+
+class day;
+class month;
+class year;
+
+class weekday;
+class weekday_indexed;
+class weekday_last;
+
+class month_day;
+class month_day_last;
+class month_weekday;
+class month_weekday_last;
+
+class year_month;
+
+class year_month_day;
+class year_month_day_last;
+class year_month_weekday;
+class year_month_weekday_last;
+
+// date composition operators
+
+CONSTCD11 year_month operator/(const year& y, const month& m) NOEXCEPT;
+CONSTCD11 year_month operator/(const year& y, int          m) NOEXCEPT;
+
+CONSTCD11 month_day operator/(const day& d, const month& m) NOEXCEPT;
+CONSTCD11 month_day operator/(const day& d, int          m) NOEXCEPT;
+CONSTCD11 month_day operator/(const month& m, const day& d) NOEXCEPT;
+CONSTCD11 month_day operator/(const month& m, int        d) NOEXCEPT;
+CONSTCD11 month_day operator/(int          m, const day& d) NOEXCEPT;
+
+CONSTCD11 month_day_last operator/(const month& m, last_spec) NOEXCEPT;
+CONSTCD11 month_day_last operator/(int          m, last_spec) NOEXCEPT;
+CONSTCD11 month_day_last operator/(last_spec, const month& m) NOEXCEPT;
+CONSTCD11 month_day_last operator/(last_spec, int          m) NOEXCEPT;
+
+CONSTCD11 month_weekday operator/(const month& m, const weekday_indexed& wdi) NOEXCEPT;
+CONSTCD11 month_weekday operator/(int          m, const weekday_indexed& wdi) NOEXCEPT;
+CONSTCD11 month_weekday operator/(const weekday_indexed& wdi, const month& m) NOEXCEPT;
+CONSTCD11 month_weekday operator/(const weekday_indexed& wdi, int          m) NOEXCEPT;
+
+CONSTCD11 month_weekday_last operator/(const month& m, const weekday_last& wdl) NOEXCEPT;
+CONSTCD11 month_weekday_last operator/(int          m, const weekday_last& wdl) NOEXCEPT;
+CONSTCD11 month_weekday_last operator/(const weekday_last& wdl, const month& m) NOEXCEPT;
+CONSTCD11 month_weekday_last operator/(const weekday_last& wdl, int          m) NOEXCEPT;
+
+CONSTCD11 year_month_day operator/(const year_month& ym, const day& d) NOEXCEPT;
+CONSTCD11 year_month_day operator/(const year_month& ym, int        d) NOEXCEPT;
+CONSTCD11 year_month_day operator/(const year& y, const month_day& md) NOEXCEPT;
+CONSTCD11 year_month_day operator/(int         y, const month_day& md) NOEXCEPT;
+CONSTCD11 year_month_day operator/(const month_day& md, const year& y) NOEXCEPT;
+CONSTCD11 year_month_day operator/(const month_day& md, int         y) NOEXCEPT;
+
+CONSTCD11
+    year_month_day_last operator/(const year_month& ym,   last_spec) NOEXCEPT;
+CONSTCD11
+    year_month_day_last operator/(const year& y, const month_day_last& mdl) NOEXCEPT;
+CONSTCD11
+    year_month_day_last operator/(int         y, const month_day_last& mdl) NOEXCEPT;
+CONSTCD11
+    year_month_day_last operator/(const month_day_last& mdl, const year& y) NOEXCEPT;
+CONSTCD11
+    year_month_day_last operator/(const month_day_last& mdl, int         y) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday
+operator/(const year_month& ym, const weekday_indexed& wdi) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday
+operator/(const year&        y, const month_weekday&   mwd) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday
+operator/(int                y, const month_weekday&   mwd) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday
+operator/(const month_weekday& mwd, const year&          y) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday
+operator/(const month_weekday& mwd, int                  y) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday_last
+operator/(const year_month& ym, const weekday_last& wdl) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday_last
+operator/(const year& y, const month_weekday_last& mwdl) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday_last
+operator/(int         y, const month_weekday_last& mwdl) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday_last
+operator/(const month_weekday_last& mwdl, const year& y) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday_last
+operator/(const month_weekday_last& mwdl, int         y) NOEXCEPT;
+
+// Detailed interface
+
+// day
+
+class day
+{
+    unsigned char d_;
+
+public:
+    explicit CONSTCD11 day(unsigned d) NOEXCEPT;
+
+    CONSTCD14 day& operator++()    NOEXCEPT;
+    CONSTCD14 day  operator++(int) NOEXCEPT;
+    CONSTCD14 day& operator--()    NOEXCEPT;
+    CONSTCD14 day  operator--(int) NOEXCEPT;
+
+    CONSTCD14 day& operator+=(const days& d) NOEXCEPT;
+    CONSTCD14 day& operator-=(const days& d) NOEXCEPT;
+
+    CONSTCD11 explicit operator unsigned() const NOEXCEPT;
+    CONSTCD11 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const day& x, const day& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const day& x, const day& y) NOEXCEPT;
+CONSTCD11 bool operator< (const day& x, const day& y) NOEXCEPT;
+CONSTCD11 bool operator> (const day& x, const day& y) NOEXCEPT;
+CONSTCD11 bool operator<=(const day& x, const day& y) NOEXCEPT;
+CONSTCD11 bool operator>=(const day& x, const day& y) NOEXCEPT;
+
+CONSTCD11 day  operator+(const day&  x, const days& y) NOEXCEPT;
+CONSTCD11 day  operator+(const days& x, const day&  y) NOEXCEPT;
+CONSTCD11 day  operator-(const day&  x, const days& y) NOEXCEPT;
+CONSTCD11 days operator-(const day&  x, const day&  y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const day& d);
+
+// month
+
+class month
+{
+    unsigned char m_;
+
+public:
+    explicit CONSTCD11 month(unsigned m) NOEXCEPT;
+
+    CONSTCD14 month& operator++()    NOEXCEPT;
+    CONSTCD14 month  operator++(int) NOEXCEPT;
+    CONSTCD14 month& operator--()    NOEXCEPT;
+    CONSTCD14 month  operator--(int) NOEXCEPT;
+
+    CONSTCD14 month& operator+=(const months& m) NOEXCEPT;
+    CONSTCD14 month& operator-=(const months& m) NOEXCEPT;
+
+    CONSTCD11 explicit operator unsigned() const NOEXCEPT;
+    CONSTCD11 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const month& x, const month& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const month& x, const month& y) NOEXCEPT;
+CONSTCD11 bool operator< (const month& x, const month& y) NOEXCEPT;
+CONSTCD11 bool operator> (const month& x, const month& y) NOEXCEPT;
+CONSTCD11 bool operator<=(const month& x, const month& y) NOEXCEPT;
+CONSTCD11 bool operator>=(const month& x, const month& y) NOEXCEPT;
+
+CONSTCD14 month  operator+(const month&  x, const months& y) NOEXCEPT;
+CONSTCD14 month  operator+(const months& x,  const month& y) NOEXCEPT;
+CONSTCD14 month  operator-(const month&  x, const months& y) NOEXCEPT;
+CONSTCD14 months operator-(const month&  x,  const month& y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const month& m);
+
+// year
+
+class year
+{
+    short y_;
+
+public:
+    explicit CONSTCD11 year(int y) NOEXCEPT;
+
+    CONSTCD14 year& operator++()    NOEXCEPT;
+    CONSTCD14 year  operator++(int) NOEXCEPT;
+    CONSTCD14 year& operator--()    NOEXCEPT;
+    CONSTCD14 year  operator--(int) NOEXCEPT;
+
+    CONSTCD14 year& operator+=(const years& y) NOEXCEPT;
+    CONSTCD14 year& operator-=(const years& y) NOEXCEPT;
+
+    CONSTCD14 bool is_leap() const NOEXCEPT;
+
+    CONSTCD11 explicit operator int() const NOEXCEPT;
+    CONSTCD11 bool ok() const NOEXCEPT;
+
+    static CONSTCD11 year min() NOEXCEPT;
+    static CONSTCD11 year max() NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const year& x, const year& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const year& x, const year& y) NOEXCEPT;
+CONSTCD11 bool operator< (const year& x, const year& y) NOEXCEPT;
+CONSTCD11 bool operator> (const year& x, const year& y) NOEXCEPT;
+CONSTCD11 bool operator<=(const year& x, const year& y) NOEXCEPT;
+CONSTCD11 bool operator>=(const year& x, const year& y) NOEXCEPT;
+
+CONSTCD11 year  operator+(const year&  x, const years& y) NOEXCEPT;
+CONSTCD11 year  operator+(const years& x, const year&  y) NOEXCEPT;
+CONSTCD11 year  operator-(const year&  x, const years& y) NOEXCEPT;
+CONSTCD11 years operator-(const year&  x, const year&  y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year& y);
+
+// weekday
+
+class weekday
+{
+    unsigned char wd_;
+public:
+    explicit CONSTCD11 weekday(unsigned wd) NOEXCEPT;
+    explicit weekday(int) = delete;
+    CONSTCD11 weekday(const sys_days& dp) NOEXCEPT;
+    CONSTCD11 explicit weekday(const local_days& dp) NOEXCEPT;
+
+    CONSTCD14 weekday& operator++()    NOEXCEPT;
+    CONSTCD14 weekday  operator++(int) NOEXCEPT;
+    CONSTCD14 weekday& operator--()    NOEXCEPT;
+    CONSTCD14 weekday  operator--(int) NOEXCEPT;
+
+    CONSTCD14 weekday& operator+=(const days& d) NOEXCEPT;
+    CONSTCD14 weekday& operator-=(const days& d) NOEXCEPT;
+
+    CONSTCD11 explicit operator unsigned() const NOEXCEPT;
+    CONSTCD11 bool ok() const NOEXCEPT;
+
+    CONSTCD11 weekday_indexed operator[](unsigned index) const NOEXCEPT;
+    CONSTCD11 weekday_last    operator[](last_spec)      const NOEXCEPT;
+
+private:
+    static CONSTCD11 unsigned char weekday_from_days(int z) NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const weekday& x, const weekday& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const weekday& x, const weekday& y) NOEXCEPT;
+
+CONSTCD14 weekday operator+(const weekday& x, const days&    y) NOEXCEPT;
+CONSTCD14 weekday operator+(const days&    x, const weekday& y) NOEXCEPT;
+CONSTCD14 weekday operator-(const weekday& x, const days&    y) NOEXCEPT;
+CONSTCD14 days    operator-(const weekday& x, const weekday& y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const weekday& wd);
+
+// weekday_indexed
+
+class weekday_indexed
+{
+    unsigned char wd_    : 4;
+    unsigned char index_ : 4;
+
+public:
+    CONSTCD11 weekday_indexed(const islamic::weekday& wd, unsigned index) NOEXCEPT;
+
+    CONSTCD11 islamic::weekday weekday() const NOEXCEPT;
+    CONSTCD11 unsigned index() const NOEXCEPT;
+    CONSTCD11 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const weekday_indexed& x, const weekday_indexed& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const weekday_indexed& x, const weekday_indexed& y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const weekday_indexed& wdi);
+
+// weekday_last
+
+class weekday_last
+{
+    islamic::weekday wd_;
+
+public:
+    explicit CONSTCD11 weekday_last(const islamic::weekday& wd) NOEXCEPT;
+
+    CONSTCD11 islamic::weekday weekday() const NOEXCEPT;
+    CONSTCD11 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const weekday_last& x, const weekday_last& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const weekday_last& x, const weekday_last& y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const weekday_last& wdl);
+
+// year_month
+
+class year_month
+{
+    islamic::year  y_;
+    islamic::month m_;
+
+public:
+    CONSTCD11 year_month(const islamic::year& y, const islamic::month& m) NOEXCEPT;
+
+    CONSTCD11 islamic::year  year()  const NOEXCEPT;
+    CONSTCD11 islamic::month month() const NOEXCEPT;
+
+    CONSTCD14 year_month& operator+=(const months& dm) NOEXCEPT;
+    CONSTCD14 year_month& operator-=(const months& dm) NOEXCEPT;
+    CONSTCD14 year_month& operator+=(const years& dy) NOEXCEPT;
+    CONSTCD14 year_month& operator-=(const years& dy) NOEXCEPT;
+
+    CONSTCD11 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const year_month& x, const year_month& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const year_month& x, const year_month& y) NOEXCEPT;
+CONSTCD11 bool operator< (const year_month& x, const year_month& y) NOEXCEPT;
+CONSTCD11 bool operator> (const year_month& x, const year_month& y) NOEXCEPT;
+CONSTCD11 bool operator<=(const year_month& x, const year_month& y) NOEXCEPT;
+CONSTCD11 bool operator>=(const year_month& x, const year_month& y) NOEXCEPT;
+
+CONSTCD14 year_month operator+(const year_month& ym, const months& dm) NOEXCEPT;
+CONSTCD14 year_month operator+(const months& dm, const year_month& ym) NOEXCEPT;
+CONSTCD14 year_month operator-(const year_month& ym, const months& dm) NOEXCEPT;
+
+CONSTCD11 months operator-(const year_month& x, const year_month& y) NOEXCEPT;
+CONSTCD11 year_month operator+(const year_month& ym, const years& dy) NOEXCEPT;
+CONSTCD11 year_month operator+(const years& dy, const year_month& ym) NOEXCEPT;
+CONSTCD11 year_month operator-(const year_month& ym, const years& dy) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_month& ym);
+
+// month_day
+
+class month_day
+{
+    islamic::month m_;
+    islamic::day   d_;
+
+public:
+    CONSTCD11 month_day(const islamic::month& m, const islamic::day& d) NOEXCEPT;
+
+    CONSTCD11 islamic::month month() const NOEXCEPT;
+    CONSTCD11 islamic::day   day() const NOEXCEPT;
+
+    CONSTCD14 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const month_day& x, const month_day& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const month_day& x, const month_day& y) NOEXCEPT;
+CONSTCD11 bool operator< (const month_day& x, const month_day& y) NOEXCEPT;
+CONSTCD11 bool operator> (const month_day& x, const month_day& y) NOEXCEPT;
+CONSTCD11 bool operator<=(const month_day& x, const month_day& y) NOEXCEPT;
+CONSTCD11 bool operator>=(const month_day& x, const month_day& y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const month_day& md);
+
+// month_day_last
+
+class month_day_last
+{
+    islamic::month m_;
+
+public:
+    CONSTCD11 explicit month_day_last(const islamic::month& m) NOEXCEPT;
+
+    CONSTCD11 islamic::month month() const NOEXCEPT;
+    CONSTCD11 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const month_day_last& x, const month_day_last& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const month_day_last& x, const month_day_last& y) NOEXCEPT;
+CONSTCD11 bool operator< (const month_day_last& x, const month_day_last& y) NOEXCEPT;
+CONSTCD11 bool operator> (const month_day_last& x, const month_day_last& y) NOEXCEPT;
+CONSTCD11 bool operator<=(const month_day_last& x, const month_day_last& y) NOEXCEPT;
+CONSTCD11 bool operator>=(const month_day_last& x, const month_day_last& y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const month_day_last& mdl);
+
+// month_weekday
+
+class month_weekday
+{
+    islamic::month           m_;
+    islamic::weekday_indexed wdi_;
+public:
+    CONSTCD11 month_weekday(const islamic::month& m,
+                            const islamic::weekday_indexed& wdi) NOEXCEPT;
+
+    CONSTCD11 islamic::month           month()           const NOEXCEPT;
+    CONSTCD11 islamic::weekday_indexed weekday_indexed() const NOEXCEPT;
+
+    CONSTCD11 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const month_weekday& x, const month_weekday& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const month_weekday& x, const month_weekday& y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const month_weekday& mwd);
+
+// month_weekday_last
+
+class month_weekday_last
+{
+    islamic::month        m_;
+    islamic::weekday_last wdl_;
+
+public:
+    CONSTCD11 month_weekday_last(const islamic::month& m,
+                                 const islamic::weekday_last& wd) NOEXCEPT;
+
+    CONSTCD11 islamic::month        month()        const NOEXCEPT;
+    CONSTCD11 islamic::weekday_last weekday_last() const NOEXCEPT;
+
+    CONSTCD11 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11
+    bool operator==(const month_weekday_last& x, const month_weekday_last& y) NOEXCEPT;
+CONSTCD11
+    bool operator!=(const month_weekday_last& x, const month_weekday_last& y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const month_weekday_last& mwdl);
+
+// class year_month_day
+
+class year_month_day
+{
+    islamic::year  y_;
+    islamic::month m_;
+    islamic::day   d_;
+
+public:
+    CONSTCD11 year_month_day(const islamic::year& y, const islamic::month& m,
+                             const islamic::day& d) NOEXCEPT;
+    CONSTCD14 year_month_day(const year_month_day_last& ymdl) NOEXCEPT;
+
+    CONSTCD14 year_month_day(sys_days dp) NOEXCEPT;
+    CONSTCD14 explicit year_month_day(local_days dp) NOEXCEPT;
+
+    CONSTCD14 year_month_day& operator+=(const months& m) NOEXCEPT;
+    CONSTCD14 year_month_day& operator-=(const months& m) NOEXCEPT;
+    CONSTCD14 year_month_day& operator+=(const years& y)  NOEXCEPT;
+    CONSTCD14 year_month_day& operator-=(const years& y)  NOEXCEPT;
+
+    CONSTCD11 islamic::year  year()  const NOEXCEPT;
+    CONSTCD11 islamic::month month() const NOEXCEPT;
+    CONSTCD11 islamic::day   day()   const NOEXCEPT;
+
+    CONSTCD14 operator sys_days() const NOEXCEPT;
+    CONSTCD14 explicit operator local_days() const NOEXCEPT;
+    CONSTCD14 bool ok() const NOEXCEPT;
+
+private:
+    static CONSTCD14 year_month_day from_days(days dp) NOEXCEPT;
+    CONSTCD14 days to_days() const NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const year_month_day& x, const year_month_day& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const year_month_day& x, const year_month_day& y) NOEXCEPT;
+CONSTCD11 bool operator< (const year_month_day& x, const year_month_day& y) NOEXCEPT;
+CONSTCD11 bool operator> (const year_month_day& x, const year_month_day& y) NOEXCEPT;
+CONSTCD11 bool operator<=(const year_month_day& x, const year_month_day& y) NOEXCEPT;
+CONSTCD11 bool operator>=(const year_month_day& x, const year_month_day& y) NOEXCEPT;
+
+CONSTCD14 year_month_day operator+(const year_month_day& ymd, const months& dm) NOEXCEPT;
+CONSTCD14 year_month_day operator+(const months& dm, const year_month_day& ymd) NOEXCEPT;
+CONSTCD14 year_month_day operator-(const year_month_day& ymd, const months& dm) NOEXCEPT;
+CONSTCD11 year_month_day operator+(const year_month_day& ymd, const years& dy)  NOEXCEPT;
+CONSTCD11 year_month_day operator+(const years& dy, const year_month_day& ymd)  NOEXCEPT;
+CONSTCD11 year_month_day operator-(const year_month_day& ymd, const years& dy)  NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_month_day& ymd);
+
+// year_month_day_last
+
+class year_month_day_last
+{
+    islamic::year           y_;
+    islamic::month_day_last mdl_;
+
+public:
+    CONSTCD11 year_month_day_last(const islamic::year& y,
+                                  const islamic::month_day_last& mdl) NOEXCEPT;
+
+    CONSTCD14 year_month_day_last& operator+=(const months& m) NOEXCEPT;
+    CONSTCD14 year_month_day_last& operator-=(const months& m) NOEXCEPT;
+    CONSTCD14 year_month_day_last& operator+=(const years& y)  NOEXCEPT;
+    CONSTCD14 year_month_day_last& operator-=(const years& y)  NOEXCEPT;
+
+    CONSTCD11 islamic::year           year()           const NOEXCEPT;
+    CONSTCD11 islamic::month          month()          const NOEXCEPT;
+    CONSTCD11 islamic::month_day_last month_day_last() const NOEXCEPT;
+    CONSTCD14 islamic::day            day()            const NOEXCEPT;
+
+    CONSTCD14 operator sys_days() const NOEXCEPT;
+    CONSTCD14 explicit operator local_days() const NOEXCEPT;
+    CONSTCD11 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11
+    bool operator==(const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT;
+CONSTCD11
+    bool operator!=(const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT;
+CONSTCD11
+    bool operator< (const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT;
+CONSTCD11
+    bool operator> (const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT;
+CONSTCD11
+    bool operator<=(const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT;
+CONSTCD11
+    bool operator>=(const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT;
+
+CONSTCD14
+year_month_day_last
+operator+(const year_month_day_last& ymdl, const months& dm) NOEXCEPT;
+
+CONSTCD14
+year_month_day_last
+operator+(const months& dm, const year_month_day_last& ymdl) NOEXCEPT;
+
+CONSTCD11
+year_month_day_last
+operator+(const year_month_day_last& ymdl, const years& dy) NOEXCEPT;
+
+CONSTCD11
+year_month_day_last
+operator+(const years& dy, const year_month_day_last& ymdl) NOEXCEPT;
+
+CONSTCD14
+year_month_day_last
+operator-(const year_month_day_last& ymdl, const months& dm) NOEXCEPT;
+
+CONSTCD11
+year_month_day_last
+operator-(const year_month_day_last& ymdl, const years& dy) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_month_day_last& ymdl);
+
+// year_month_weekday
+
+class year_month_weekday
+{
+    islamic::year            y_;
+    islamic::month           m_;
+    islamic::weekday_indexed wdi_;
+
+public:
+    CONSTCD11 year_month_weekday(const islamic::year& y, const islamic::month& m,
+                                   const islamic::weekday_indexed& wdi) NOEXCEPT;
+    CONSTCD14 year_month_weekday(const sys_days& dp) NOEXCEPT;
+    CONSTCD14 explicit year_month_weekday(const local_days& dp) NOEXCEPT;
+
+    CONSTCD14 year_month_weekday& operator+=(const months& m) NOEXCEPT;
+    CONSTCD14 year_month_weekday& operator-=(const months& m) NOEXCEPT;
+    CONSTCD14 year_month_weekday& operator+=(const years& y)  NOEXCEPT;
+    CONSTCD14 year_month_weekday& operator-=(const years& y)  NOEXCEPT;
+
+    CONSTCD11 islamic::year year() const NOEXCEPT;
+    CONSTCD11 islamic::month month() const NOEXCEPT;
+    CONSTCD11 islamic::weekday weekday() const NOEXCEPT;
+    CONSTCD11 unsigned index() const NOEXCEPT;
+    CONSTCD11 islamic::weekday_indexed weekday_indexed() const NOEXCEPT;
+
+    CONSTCD14 operator sys_days() const NOEXCEPT;
+    CONSTCD14 explicit operator local_days() const NOEXCEPT;
+    CONSTCD14 bool ok() const NOEXCEPT;
+
+private:
+    static CONSTCD14 year_month_weekday from_days(days dp) NOEXCEPT;
+    CONSTCD14 days to_days() const NOEXCEPT;
+};
+
+CONSTCD11
+    bool operator==(const year_month_weekday& x, const year_month_weekday& y) NOEXCEPT;
+CONSTCD11
+    bool operator!=(const year_month_weekday& x, const year_month_weekday& y) NOEXCEPT;
+
+CONSTCD14
+year_month_weekday
+operator+(const year_month_weekday& ymwd, const months& dm) NOEXCEPT;
+
+CONSTCD14
+year_month_weekday
+operator+(const months& dm, const year_month_weekday& ymwd) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday
+operator+(const year_month_weekday& ymwd, const years& dy) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday
+operator+(const years& dy, const year_month_weekday& ymwd) NOEXCEPT;
+
+CONSTCD14
+year_month_weekday
+operator-(const year_month_weekday& ymwd, const months& dm) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday
+operator-(const year_month_weekday& ymwd, const years& dy) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_month_weekday& ymwdi);
+
+// year_month_weekday_last
+
+class year_month_weekday_last
+{
+    islamic::year y_;
+    islamic::month m_;
+    islamic::weekday_last wdl_;
+
+public:
+    CONSTCD11 year_month_weekday_last(const islamic::year& y, const islamic::month& m,
+                                      const islamic::weekday_last& wdl) NOEXCEPT;
+
+    CONSTCD14 year_month_weekday_last& operator+=(const months& m) NOEXCEPT;
+    CONSTCD14 year_month_weekday_last& operator-=(const months& m) NOEXCEPT;
+    CONSTCD14 year_month_weekday_last& operator+=(const years& y) NOEXCEPT;
+    CONSTCD14 year_month_weekday_last& operator-=(const years& y) NOEXCEPT;
+
+    CONSTCD11 islamic::year year() const NOEXCEPT;
+    CONSTCD11 islamic::month month() const NOEXCEPT;
+    CONSTCD11 islamic::weekday weekday() const NOEXCEPT;
+    CONSTCD11 islamic::weekday_last weekday_last() const NOEXCEPT;
+
+    CONSTCD14 operator sys_days() const NOEXCEPT;
+    CONSTCD14 explicit operator local_days() const NOEXCEPT;
+    CONSTCD11 bool ok() const NOEXCEPT;
+
+private:
+    CONSTCD14 days to_days() const NOEXCEPT;
+};
+
+CONSTCD11
+bool
+operator==(const year_month_weekday_last& x, const year_month_weekday_last& y) NOEXCEPT;
+
+CONSTCD11
+bool
+operator!=(const year_month_weekday_last& x, const year_month_weekday_last& y) NOEXCEPT;
+
+CONSTCD14
+year_month_weekday_last
+operator+(const year_month_weekday_last& ymwdl, const months& dm) NOEXCEPT;
+
+CONSTCD14
+year_month_weekday_last
+operator+(const months& dm, const year_month_weekday_last& ymwdl) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday_last
+operator+(const year_month_weekday_last& ymwdl, const years& dy) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday_last
+operator+(const years& dy, const year_month_weekday_last& ymwdl) NOEXCEPT;
+
+CONSTCD14
+year_month_weekday_last
+operator-(const year_month_weekday_last& ymwdl, const months& dm) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday_last
+operator-(const year_month_weekday_last& ymwdl, const years& dy) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_month_weekday_last& ymwdl);
+
+#if !defined(_MSC_VER) || (_MSC_VER >= 1900)
+inline namespace literals
+{
+
+CONSTCD11 islamic::day  operator "" _d(unsigned long long d) NOEXCEPT;
+CONSTCD11 islamic::year operator "" _y(unsigned long long y) NOEXCEPT;
+
+}  // inline namespace literals
+#endif // !defined(_MSC_VER) || (_MSC_VER >= 1900)
+
+//----------------+
+// Implementation |
+//----------------+
+
+// day
+
+CONSTCD11 inline day::day(unsigned d) NOEXCEPT : d_(static_cast<unsigned char>(d)) {}
+CONSTCD14 inline day& day::operator++() NOEXCEPT {++d_; return *this;}
+CONSTCD14 inline day day::operator++(int) NOEXCEPT {auto tmp(*this); ++(*this); return tmp;}
+CONSTCD14 inline day& day::operator--() NOEXCEPT {--d_; return *this;}
+CONSTCD14 inline day day::operator--(int) NOEXCEPT {auto tmp(*this); --(*this); return tmp;}
+CONSTCD14 inline day& day::operator+=(const days& d) NOEXCEPT {*this = *this + d; return *this;}
+CONSTCD14 inline day& day::operator-=(const days& d) NOEXCEPT {*this = *this - d; return *this;}
+CONSTCD11 inline day::operator unsigned() const NOEXCEPT {return d_;}
+CONSTCD11 inline bool day::ok() const NOEXCEPT {return 1 <= d_ && d_ <= 30;}
+
+CONSTCD11
+inline
+bool
+operator==(const day& x, const day& y) NOEXCEPT
+{
+    return static_cast<unsigned>(x) == static_cast<unsigned>(y);
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const day& x, const day& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+CONSTCD11
+inline
+bool
+operator<(const day& x, const day& y) NOEXCEPT
+{
+    return static_cast<unsigned>(x) < static_cast<unsigned>(y);
+}
+
+CONSTCD11
+inline
+bool
+operator>(const day& x, const day& y) NOEXCEPT
+{
+    return y < x;
+}
+
+CONSTCD11
+inline
+bool
+operator<=(const day& x, const day& y) NOEXCEPT
+{
+    return !(y < x);
+}
+
+CONSTCD11
+inline
+bool
+operator>=(const day& x, const day& y) NOEXCEPT
+{
+    return !(x < y);
+}
+
+CONSTCD11
+inline
+days
+operator-(const day& x, const day& y) NOEXCEPT
+{
+    return days{static_cast<days::rep>(static_cast<unsigned>(x)
+                                     - static_cast<unsigned>(y))};
+}
+
+CONSTCD11
+inline
+day
+operator+(const day& x, const days& y) NOEXCEPT
+{
+    return day{static_cast<unsigned>(x) + static_cast<unsigned>(y.count())};
+}
+
+CONSTCD11
+inline
+day
+operator+(const days& x, const day& y) NOEXCEPT
+{
+    return y + x;
+}
+
+CONSTCD11
+inline
+day
+operator-(const day& x, const days& y) NOEXCEPT
+{
+    return x + -y;
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const day& d)
+{
+    date::detail::save_ostream<CharT, Traits> _(os);
+    os.fill('0');
+    os.flags(std::ios::dec | std::ios::right);
+    os.width(2);
+    os << static_cast<unsigned>(d);
+    return os;
+}
+
+// month
+
+CONSTCD11 inline month::month(unsigned m) NOEXCEPT : m_(static_cast<decltype(m_)>(m)) {}
+CONSTCD14 inline month& month::operator++() NOEXCEPT {if (++m_ == 13) m_ = 1; return *this;}
+CONSTCD14 inline month month::operator++(int) NOEXCEPT {auto tmp(*this); ++(*this); return tmp;}
+CONSTCD14 inline month& month::operator--() NOEXCEPT {if (--m_ == 0) m_ = 12; return *this;}
+CONSTCD14 inline month month::operator--(int) NOEXCEPT {auto tmp(*this); --(*this); return tmp;}
+
+CONSTCD14
+inline
+month&
+month::operator+=(const months& m) NOEXCEPT
+{
+    *this = *this + m;
+    return *this;
+}
+
+CONSTCD14
+inline
+month&
+month::operator-=(const months& m) NOEXCEPT
+{
+    *this = *this - m;
+    return *this;
+}
+
+CONSTCD11 inline month::operator unsigned() const NOEXCEPT {return m_;}
+CONSTCD11 inline bool month::ok() const NOEXCEPT {return 1 <= m_ && m_ <= 12;}
+
+CONSTCD11
+inline
+bool
+operator==(const month& x, const month& y) NOEXCEPT
+{
+    return static_cast<unsigned>(x) == static_cast<unsigned>(y);
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const month& x, const month& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+CONSTCD11
+inline
+bool
+operator<(const month& x, const month& y) NOEXCEPT
+{
+    return static_cast<unsigned>(x) < static_cast<unsigned>(y);
+}
+
+CONSTCD11
+inline
+bool
+operator>(const month& x, const month& y) NOEXCEPT
+{
+    return y < x;
+}
+
+CONSTCD11
+inline
+bool
+operator<=(const month& x, const month& y) NOEXCEPT
+{
+    return !(y < x);
+}
+
+CONSTCD11
+inline
+bool
+operator>=(const month& x, const month& y) NOEXCEPT
+{
+    return !(x < y);
+}
+
+CONSTCD14
+inline
+months
+operator-(const month& x, const month& y) NOEXCEPT
+{
+    auto const d = static_cast<unsigned>(x) - static_cast<unsigned>(y);
+    return months(d <= 11 ? d : d + 12);
+}
+
+CONSTCD14
+inline
+month
+operator+(const month& x, const months& y) NOEXCEPT
+{
+    auto const mu = static_cast<long long>(static_cast<unsigned>(x)) - 1 + y.count();
+    auto const yr = (mu >= 0 ? mu : mu-11) / 12;
+    return month{static_cast<unsigned>(mu - yr * 12 + 1)};
+}
+
+CONSTCD14
+inline
+month
+operator+(const months& x, const month& y) NOEXCEPT
+{
+    return y + x;
+}
+
+CONSTCD14
+inline
+month
+operator-(const month& x, const months& y) NOEXCEPT
+{
+    return x + -y;
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const month& m)
+{
+    switch (static_cast<unsigned>(m))
+    {
+    case 1:
+        os << "Muharram";
+        break;
+    case 2:
+        os << "Safar";
+        break;
+    case 3:
+        os << "Rabi' al-awwal";
+        break;
+    case 4:
+        os << "Rabi' al-thani";
+        break;
+    case 5:
+        os << "Jumada al-awwal";
+        break;
+    case 6:
+        os << "Jumada al-Thani";
+        break;
+    case 7:
+        os << "Rajab";
+        break;
+    case 8:
+        os << "Sha'ban";
+        break;
+    case 9:
+        os << "Ramadan";
+        break;
+    case 10:
+        os << "Shawwal";
+        break;
+    case 11:
+        os << "Dhu al-Qi'dah";
+        break;
+    case 12:
+        os << "Dhu al-Hijjah";
+        break;
+    default:
+        os << static_cast<unsigned>(m) << " is not a valid month";
+        break;
+    }
+    return os;
+}
+
+// year
+
+CONSTCD11 inline year::year(int y) NOEXCEPT : y_(static_cast<decltype(y_)>(y)) {}
+CONSTCD14 inline year& year::operator++() NOEXCEPT {++y_; return *this;}
+CONSTCD14 inline year year::operator++(int) NOEXCEPT {auto tmp(*this); ++(*this); return tmp;}
+CONSTCD14 inline year& year::operator--() NOEXCEPT {--y_; return *this;}
+CONSTCD14 inline year year::operator--(int) NOEXCEPT {auto tmp(*this); --(*this); return tmp;}
+CONSTCD14 inline year& year::operator+=(const years& y) NOEXCEPT {*this = *this + y; return *this;}
+CONSTCD14 inline year& year::operator-=(const years& y) NOEXCEPT {*this = *this - y; return *this;}
+
+CONSTCD14
+inline
+bool
+year::is_leap() const NOEXCEPT
+{
+    int y = y_ - 1;
+    const int era = (y >= 0 ? y : y-29) / 30;
+    const unsigned yoe = static_cast<unsigned>(y - era * 30);
+    switch (yoe)
+    {
+    case 1:
+    case 4:
+    case 6:
+    case 9:
+    case 12:
+    case 15:
+    case 17:
+    case 20:
+    case 23:
+    case 25:
+    case 28:
+        return true;
+    default:
+        return false;
+    }
+}
+
+CONSTCD11 inline year::operator int() const NOEXCEPT {return y_;}
+CONSTCD11 inline bool year::ok() const NOEXCEPT {return true;}
+
+CONSTCD11
+inline
+year
+year::min() NOEXCEPT
+{
+    return year{std::numeric_limits<short>::min()};
+}
+
+CONSTCD11
+inline
+year
+year::max() NOEXCEPT
+{
+    return year{std::numeric_limits<short>::max()};
+}
+
+CONSTCD11
+inline
+bool
+operator==(const year& x, const year& y) NOEXCEPT
+{
+    return static_cast<int>(x) == static_cast<int>(y);
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const year& x, const year& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+CONSTCD11
+inline
+bool
+operator<(const year& x, const year& y) NOEXCEPT
+{
+    return static_cast<int>(x) < static_cast<int>(y);
+}
+
+CONSTCD11
+inline
+bool
+operator>(const year& x, const year& y) NOEXCEPT
+{
+    return y < x;
+}
+
+CONSTCD11
+inline
+bool
+operator<=(const year& x, const year& y) NOEXCEPT
+{
+    return !(y < x);
+}
+
+CONSTCD11
+inline
+bool
+operator>=(const year& x, const year& y) NOEXCEPT
+{
+    return !(x < y);
+}
+
+CONSTCD11
+inline
+years
+operator-(const year& x, const year& y) NOEXCEPT
+{
+    return years{static_cast<int>(x) - static_cast<int>(y)};
+}
+
+CONSTCD11
+inline
+year
+operator+(const year& x, const years& y) NOEXCEPT
+{
+    return year{static_cast<int>(x) + y.count()};
+}
+
+CONSTCD11
+inline
+year
+operator+(const years& x, const year& y) NOEXCEPT
+{
+    return y + x;
+}
+
+CONSTCD11
+inline
+year
+operator-(const year& x, const years& y) NOEXCEPT
+{
+    return year{static_cast<int>(x) - y.count()};
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year& y)
+{
+    date::detail::save_ostream<CharT, Traits> _(os);
+    os.fill('0');
+    os.flags(std::ios::dec | std::ios::internal);
+    os.width(4 + (y < year{0}));
+    os << static_cast<int>(y);
+    return os;
+}
+
+// weekday
+
+CONSTCD11
+inline
+unsigned char
+weekday::weekday_from_days(int z) NOEXCEPT
+{
+    return static_cast<unsigned char>(static_cast<unsigned>(
+        z >= -4 ? (z+4) % 7 : (z+5) % 7 + 6));
+}
+
+CONSTCD11
+inline
+weekday::weekday(unsigned wd) NOEXCEPT
+    : wd_(static_cast<decltype(wd_)>(wd))
+    {}
+
+CONSTCD11
+inline
+weekday::weekday(const sys_days& dp) NOEXCEPT
+    : wd_(weekday_from_days(dp.time_since_epoch().count()))
+    {}
+
+CONSTCD11
+inline
+weekday::weekday(const local_days& dp) NOEXCEPT
+    : wd_(weekday_from_days(dp.time_since_epoch().count()))
+    {}
+
+CONSTCD14 inline weekday& weekday::operator++() NOEXCEPT {if (++wd_ == 7) wd_ = 0; return *this;}
+CONSTCD14 inline weekday weekday::operator++(int) NOEXCEPT {auto tmp(*this); ++(*this); return tmp;}
+CONSTCD14 inline weekday& weekday::operator--() NOEXCEPT {if (wd_-- == 0) wd_ = 6; return *this;}
+CONSTCD14 inline weekday weekday::operator--(int) NOEXCEPT {auto tmp(*this); --(*this); return tmp;}
+
+CONSTCD14
+inline
+weekday&
+weekday::operator+=(const days& d) NOEXCEPT
+{
+    *this = *this + d;
+    return *this;
+}
+
+CONSTCD14
+inline
+weekday&
+weekday::operator-=(const days& d) NOEXCEPT
+{
+    *this = *this - d;
+    return *this;
+}
+
+CONSTCD11
+inline
+weekday::operator unsigned() const NOEXCEPT
+{
+    return static_cast<unsigned>(wd_);
+}
+
+CONSTCD11 inline bool weekday::ok() const NOEXCEPT {return wd_ <= 6;}
+
+CONSTCD11
+inline
+bool
+operator==(const weekday& x, const weekday& y) NOEXCEPT
+{
+    return static_cast<unsigned>(x) == static_cast<unsigned>(y);
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const weekday& x, const weekday& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+CONSTCD14
+inline
+days
+operator-(const weekday& x, const weekday& y) NOEXCEPT
+{
+    auto const diff = static_cast<unsigned>(x) - static_cast<unsigned>(y);
+    return days{diff <= 6 ? diff : diff + 7};
+}
+
+CONSTCD14
+inline
+weekday
+operator+(const weekday& x, const days& y) NOEXCEPT
+{
+    auto const wdu = static_cast<long long>(static_cast<unsigned>(x)) + y.count();
+    auto const wk = (wdu >= 0 ? wdu : wdu-6) / 7;
+    return weekday{static_cast<unsigned>(wdu - wk * 7)};
+}
+
+CONSTCD14
+inline
+weekday
+operator+(const days& x, const weekday& y) NOEXCEPT
+{
+    return y + x;
+}
+
+CONSTCD14
+inline
+weekday
+operator-(const weekday& x, const days& y) NOEXCEPT
+{
+    return x + -y;
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const weekday& wd)
+{
+    switch (static_cast<unsigned>(wd))
+    {
+    case 0:
+        os << "al-Aḥad";
+        break;
+    case 1:
+        os << "al-Ithnayn";
+        break;
+    case 2:
+        os << "ath-Thulāthā’";
+        break;
+    case 3:
+        os << "al-Arba‘ā’";
+        break;
+    case 4:
+        os << "al-Khamīs";
+        break;
+    case 5:
+        os << "al-Jum‘ah";
+        break;
+    case 6:
+        os << "as-Sabt";
+        break;
+    default:
+        os << static_cast<unsigned>(wd) << " is not a valid weekday";
+        break;
+    }
+    return os;
+}
+
+#if !defined(_MSC_VER) || (_MSC_VER >= 1900)
+inline namespace literals
+{
+
+CONSTCD11
+inline
+islamic::day
+operator "" _d(unsigned long long d) NOEXCEPT
+{
+    return islamic::day{static_cast<unsigned>(d)};
+}
+
+CONSTCD11
+inline
+islamic::year
+operator "" _y(unsigned long long y) NOEXCEPT
+{
+    return islamic::year(static_cast<int>(y));
+}
+#endif  // !defined(_MSC_VER) || (_MSC_VER >= 1900)
+
+CONSTDATA islamic::last_spec last{};
+
+#if !defined(_MSC_VER) || (_MSC_VER >= 1900)
+}  // inline namespace literals
+#endif
+
+// weekday_indexed
+
+CONSTCD11
+inline
+weekday
+weekday_indexed::weekday() const NOEXCEPT
+{
+    return islamic::weekday{static_cast<unsigned>(wd_)};
+}
+
+CONSTCD11 inline unsigned weekday_indexed::index() const NOEXCEPT {return index_;}
+
+CONSTCD11
+inline
+bool
+weekday_indexed::ok() const NOEXCEPT
+{
+    return weekday().ok() && 1 <= index_ && index_ <= 5;
+}
+
+CONSTCD11
+inline
+weekday_indexed::weekday_indexed(const islamic::weekday& wd, unsigned index) NOEXCEPT
+    : wd_(static_cast<decltype(wd_)>(static_cast<unsigned>(wd)))
+    , index_(static_cast<decltype(index_)>(index))
+    {}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const weekday_indexed& wdi)
+{
+    return os << wdi.weekday() << '[' << wdi.index() << ']';
+}
+
+CONSTCD11
+inline
+weekday_indexed
+weekday::operator[](unsigned index) const NOEXCEPT
+{
+    return {*this, index};
+}
+
+CONSTCD11
+inline
+bool
+operator==(const weekday_indexed& x, const weekday_indexed& y) NOEXCEPT
+{
+    return x.weekday() == y.weekday() && x.index() == y.index();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const weekday_indexed& x, const weekday_indexed& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+// weekday_last
+
+CONSTCD11 inline islamic::weekday weekday_last::weekday() const NOEXCEPT {return wd_;}
+CONSTCD11 inline bool weekday_last::ok() const NOEXCEPT {return wd_.ok();}
+CONSTCD11 inline weekday_last::weekday_last(const islamic::weekday& wd) NOEXCEPT : wd_(wd) {}
+
+CONSTCD11
+inline
+bool
+operator==(const weekday_last& x, const weekday_last& y) NOEXCEPT
+{
+    return x.weekday() == y.weekday();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const weekday_last& x, const weekday_last& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const weekday_last& wdl)
+{
+    return os << wdl.weekday() << "[last]";
+}
+
+CONSTCD11
+inline
+weekday_last
+weekday::operator[](last_spec) const NOEXCEPT
+{
+    return weekday_last{*this};
+}
+
+// year_month
+
+CONSTCD11
+inline
+year_month::year_month(const islamic::year& y, const islamic::month& m) NOEXCEPT
+    : y_(y)
+    , m_(m)
+    {}
+
+CONSTCD11 inline year year_month::year() const NOEXCEPT {return y_;}
+CONSTCD11 inline month year_month::month() const NOEXCEPT {return m_;}
+CONSTCD11 inline bool year_month::ok() const NOEXCEPT {return y_.ok() && m_.ok();}
+
+CONSTCD14
+inline
+year_month&
+year_month::operator+=(const months& dm) NOEXCEPT
+{
+    *this = *this + dm;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month&
+year_month::operator-=(const months& dm) NOEXCEPT
+{
+    *this = *this - dm;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month&
+year_month::operator+=(const years& dy) NOEXCEPT
+{
+    *this = *this + dy;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month&
+year_month::operator-=(const years& dy) NOEXCEPT
+{
+    *this = *this - dy;
+    return *this;
+}
+
+CONSTCD11
+inline
+bool
+operator==(const year_month& x, const year_month& y) NOEXCEPT
+{
+    return x.year() == y.year() && x.month() == y.month();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const year_month& x, const year_month& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+CONSTCD11
+inline
+bool
+operator<(const year_month& x, const year_month& y) NOEXCEPT
+{
+    return x.year() < y.year() ? true
+        : (x.year() > y.year() ? false
+        : (x.month() < y.month()));
+}
+
+CONSTCD11
+inline
+bool
+operator>(const year_month& x, const year_month& y) NOEXCEPT
+{
+    return y < x;
+}
+
+CONSTCD11
+inline
+bool
+operator<=(const year_month& x, const year_month& y) NOEXCEPT
+{
+    return !(y < x);
+}
+
+CONSTCD11
+inline
+bool
+operator>=(const year_month& x, const year_month& y) NOEXCEPT
+{
+    return !(x < y);
+}
+
+CONSTCD14
+inline
+year_month
+operator+(const year_month& ym, const months& dm) NOEXCEPT
+{
+    auto dmi = static_cast<int>(static_cast<unsigned>(ym.month())) - 1 + dm.count();
+    auto dy = (dmi >= 0 ? dmi : dmi-11) / 12;
+    dmi = dmi - dy * 12 + 1;
+    return (ym.year() + years(dy)) / month(static_cast<unsigned>(dmi));
+}
+
+CONSTCD14
+inline
+year_month
+operator+(const months& dm, const year_month& ym) NOEXCEPT
+{
+    return ym + dm;
+}
+
+CONSTCD14
+inline
+year_month
+operator-(const year_month& ym, const months& dm) NOEXCEPT
+{
+    return ym + -dm;
+}
+
+CONSTCD11
+inline
+months
+operator-(const year_month& x, const year_month& y) NOEXCEPT
+{
+    return (x.year() - y.year()) +
+            months(static_cast<unsigned>(x.month()) - static_cast<unsigned>(y.month()));
+}
+
+CONSTCD11
+inline
+year_month
+operator+(const year_month& ym, const years& dy) NOEXCEPT
+{
+    return (ym.year() + dy) / ym.month();
+}
+
+CONSTCD11
+inline
+year_month
+operator+(const years& dy, const year_month& ym) NOEXCEPT
+{
+    return ym + dy;
+}
+
+CONSTCD11
+inline
+year_month
+operator-(const year_month& ym, const years& dy) NOEXCEPT
+{
+    return ym + -dy;
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_month& ym)
+{
+    return os << ym.year() << '/' << ym.month();
+}
+
+// month_day
+
+CONSTCD11
+inline
+month_day::month_day(const islamic::month& m, const islamic::day& d) NOEXCEPT
+    : m_(m)
+    , d_(d)
+    {}
+
+CONSTCD11 inline islamic::month month_day::month() const NOEXCEPT {return m_;}
+CONSTCD11 inline islamic::day month_day::day() const NOEXCEPT {return d_;}
+
+CONSTCD14
+inline
+bool
+month_day::ok() const NOEXCEPT
+{
+    CONSTDATA islamic::day d[] =
+        {30_d, 29_d, 30_d, 29_d, 30_d, 29_d, 30_d, 29_d, 30_d, 29_d, 30_d, 30_d};
+    return m_.ok() && 1_d <= d_ && d_ <= d[static_cast<unsigned>(m_)-1];
+}
+
+CONSTCD11
+inline
+bool
+operator==(const month_day& x, const month_day& y) NOEXCEPT
+{
+    return x.month() == y.month() && x.day() == y.day();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const month_day& x, const month_day& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+CONSTCD11
+inline
+bool
+operator<(const month_day& x, const month_day& y) NOEXCEPT
+{
+    return x.month() < y.month() ? true
+        : (x.month() > y.month() ? false
+        : (x.day() < y.day()));
+}
+
+CONSTCD11
+inline
+bool
+operator>(const month_day& x, const month_day& y) NOEXCEPT
+{
+    return y < x;
+}
+
+CONSTCD11
+inline
+bool
+operator<=(const month_day& x, const month_day& y) NOEXCEPT
+{
+    return !(y < x);
+}
+
+CONSTCD11
+inline
+bool
+operator>=(const month_day& x, const month_day& y) NOEXCEPT
+{
+    return !(x < y);
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const month_day& md)
+{
+    return os << md.month() << '/' << md.day();
+}
+
+// month_day_last
+
+CONSTCD11 inline month month_day_last::month() const NOEXCEPT {return m_;}
+CONSTCD11 inline bool month_day_last::ok() const NOEXCEPT {return m_.ok();}
+CONSTCD11 inline month_day_last::month_day_last(const islamic::month& m) NOEXCEPT : m_(m) {}
+
+CONSTCD11
+inline
+bool
+operator==(const month_day_last& x, const month_day_last& y) NOEXCEPT
+{
+    return x.month() == y.month();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const month_day_last& x, const month_day_last& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+CONSTCD11
+inline
+bool
+operator<(const month_day_last& x, const month_day_last& y) NOEXCEPT
+{
+    return x.month() < y.month();
+}
+
+CONSTCD11
+inline
+bool
+operator>(const month_day_last& x, const month_day_last& y) NOEXCEPT
+{
+    return y < x;
+}
+
+CONSTCD11
+inline
+bool
+operator<=(const month_day_last& x, const month_day_last& y) NOEXCEPT
+{
+    return !(y < x);
+}
+
+CONSTCD11
+inline
+bool
+operator>=(const month_day_last& x, const month_day_last& y) NOEXCEPT
+{
+    return !(x < y);
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const month_day_last& mdl)
+{
+    return os << mdl.month() << "/last";
+}
+
+// month_weekday
+
+CONSTCD11
+inline
+month_weekday::month_weekday(const islamic::month& m,
+                             const islamic::weekday_indexed& wdi) NOEXCEPT
+    : m_(m)
+    , wdi_(wdi)
+    {}
+
+CONSTCD11 inline month month_weekday::month() const NOEXCEPT {return m_;}
+
+CONSTCD11
+inline
+weekday_indexed
+month_weekday::weekday_indexed() const NOEXCEPT
+{
+    return wdi_;
+}
+
+CONSTCD11
+inline
+bool
+month_weekday::ok() const NOEXCEPT
+{
+    return m_.ok() && wdi_.ok();
+}
+
+CONSTCD11
+inline
+bool
+operator==(const month_weekday& x, const month_weekday& y) NOEXCEPT
+{
+    return x.month() == y.month() && x.weekday_indexed() == y.weekday_indexed();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const month_weekday& x, const month_weekday& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const month_weekday& mwd)
+{
+    return os << mwd.month() << '/' << mwd.weekday_indexed();
+}
+
+// month_weekday_last
+
+CONSTCD11
+inline
+month_weekday_last::month_weekday_last(const islamic::month& m,
+                                       const islamic::weekday_last& wdl) NOEXCEPT
+    : m_(m)
+    , wdl_(wdl)
+    {}
+
+CONSTCD11 inline month month_weekday_last::month() const NOEXCEPT {return m_;}
+
+CONSTCD11
+inline
+weekday_last
+month_weekday_last::weekday_last() const NOEXCEPT
+{
+    return wdl_;
+}
+
+CONSTCD11
+inline
+bool
+month_weekday_last::ok() const NOEXCEPT
+{
+    return m_.ok() && wdl_.ok();
+}
+
+CONSTCD11
+inline
+bool
+operator==(const month_weekday_last& x, const month_weekday_last& y) NOEXCEPT
+{
+    return x.month() == y.month() && x.weekday_last() == y.weekday_last();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const month_weekday_last& x, const month_weekday_last& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const month_weekday_last& mwdl)
+{
+    return os << mwdl.month() << '/' << mwdl.weekday_last();
+}
+
+// year_month_day_last
+
+CONSTCD11
+inline
+year_month_day_last::year_month_day_last(const islamic::year& y,
+                                         const islamic::month_day_last& mdl) NOEXCEPT
+    : y_(y)
+    , mdl_(mdl)
+    {}
+
+CONSTCD14
+inline
+year_month_day_last&
+year_month_day_last::operator+=(const months& m) NOEXCEPT
+{
+    *this = *this + m;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month_day_last&
+year_month_day_last::operator-=(const months& m) NOEXCEPT
+{
+    *this = *this - m;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month_day_last&
+year_month_day_last::operator+=(const years& y) NOEXCEPT
+{
+    *this = *this + y;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month_day_last&
+year_month_day_last::operator-=(const years& y) NOEXCEPT
+{
+    *this = *this - y;
+    return *this;
+}
+
+CONSTCD11 inline year year_month_day_last::year() const NOEXCEPT {return y_;}
+CONSTCD11 inline month year_month_day_last::month() const NOEXCEPT {return mdl_.month();}
+
+CONSTCD11
+inline
+month_day_last
+year_month_day_last::month_day_last() const NOEXCEPT
+{
+    return mdl_;
+}
+
+CONSTCD14
+inline
+day
+year_month_day_last::day() const NOEXCEPT
+{
+    CONSTDATA islamic::day d[] =
+        {30_d, 29_d, 30_d, 29_d, 30_d, 29_d, 30_d, 29_d, 30_d, 29_d, 30_d, 29_d};
+    return month() != islamic::month(12) || !y_.is_leap() ?
+               d[static_cast<unsigned>(month())-1] : 30_d;
+}
+
+CONSTCD14
+inline
+year_month_day_last::operator sys_days() const NOEXCEPT
+{
+    return sys_days(year()/month()/day());
+}
+
+CONSTCD14
+inline
+year_month_day_last::operator local_days() const NOEXCEPT
+{
+    return local_days(year()/month()/day());
+}
+
+CONSTCD11
+inline
+bool
+year_month_day_last::ok() const NOEXCEPT
+{
+    return y_.ok() && mdl_.ok();
+}
+
+CONSTCD11
+inline
+bool
+operator==(const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT
+{
+    return x.year() == y.year() && x.month_day_last() == y.month_day_last();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+CONSTCD11
+inline
+bool
+operator<(const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT
+{
+    return x.year() < y.year() ? true
+        : (x.year() > y.year() ? false
+        : (x.month_day_last() < y.month_day_last()));
+}
+
+CONSTCD11
+inline
+bool
+operator>(const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT
+{
+    return y < x;
+}
+
+CONSTCD11
+inline
+bool
+operator<=(const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT
+{
+    return !(y < x);
+}
+
+CONSTCD11
+inline
+bool
+operator>=(const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT
+{
+    return !(x < y);
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_month_day_last& ymdl)
+{
+    return os << ymdl.year() << '/' << ymdl.month_day_last();
+}
+
+CONSTCD14
+inline
+year_month_day_last
+operator+(const year_month_day_last& ymdl, const months& dm) NOEXCEPT
+{
+    return (ymdl.year() / ymdl.month() + dm) / last;
+}
+
+CONSTCD14
+inline
+year_month_day_last
+operator+(const months& dm, const year_month_day_last& ymdl) NOEXCEPT
+{
+    return ymdl + dm;
+}
+
+CONSTCD14
+inline
+year_month_day_last
+operator-(const year_month_day_last& ymdl, const months& dm) NOEXCEPT
+{
+    return ymdl + (-dm);
+}
+
+CONSTCD11
+inline
+year_month_day_last
+operator+(const year_month_day_last& ymdl, const years& dy) NOEXCEPT
+{
+    return {ymdl.year()+dy, ymdl.month_day_last()};
+}
+
+CONSTCD11
+inline
+year_month_day_last
+operator+(const years& dy, const year_month_day_last& ymdl) NOEXCEPT
+{
+    return ymdl + dy;
+}
+
+CONSTCD11
+inline
+year_month_day_last
+operator-(const year_month_day_last& ymdl, const years& dy) NOEXCEPT
+{
+    return ymdl + (-dy);
+}
+
+// year_month_day
+
+CONSTCD11
+inline
+year_month_day::year_month_day(const islamic::year& y, const islamic::month& m,
+                               const islamic::day& d) NOEXCEPT
+    : y_(y)
+    , m_(m)
+    , d_(d)
+    {}
+
+CONSTCD14
+inline
+year_month_day::year_month_day(const year_month_day_last& ymdl) NOEXCEPT
+    : y_(ymdl.year())
+    , m_(ymdl.month())
+    , d_(ymdl.day())
+    {}
+
+CONSTCD14
+inline
+year_month_day::year_month_day(sys_days dp) NOEXCEPT
+    : year_month_day(from_days(dp.time_since_epoch()))
+    {}
+
+CONSTCD14
+inline
+year_month_day::year_month_day(local_days dp) NOEXCEPT
+    : year_month_day(from_days(dp.time_since_epoch()))
+    {}
+
+CONSTCD11 inline year year_month_day::year() const NOEXCEPT {return y_;}
+CONSTCD11 inline month year_month_day::month() const NOEXCEPT {return m_;}
+CONSTCD11 inline day year_month_day::day() const NOEXCEPT {return d_;}
+
+CONSTCD14
+inline
+year_month_day&
+year_month_day::operator+=(const months& m) NOEXCEPT
+{
+    *this = *this + m;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month_day&
+year_month_day::operator-=(const months& m) NOEXCEPT
+{
+    *this = *this - m;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month_day&
+year_month_day::operator+=(const years& y) NOEXCEPT
+{
+    *this = *this + y;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month_day&
+year_month_day::operator-=(const years& y) NOEXCEPT
+{
+    *this = *this - y;
+    return *this;
+}
+
+CONSTCD14
+inline
+days
+year_month_day::to_days() const NOEXCEPT
+{
+    static_assert(std::numeric_limits<unsigned>::digits >= 18,
+             "This algorithm has not been ported to a 16 bit unsigned integer");
+    static_assert(std::numeric_limits<int>::digits >= 20,
+             "This algorithm has not been ported to a 16 bit signed integer");
+    auto const y = static_cast<int>(y_) - 1;
+    auto const m = static_cast<unsigned>(m_);
+    auto const d = static_cast<unsigned>(d_);
+    auto const era = (y >= 0 ? y : y-29) / 30;
+    auto const yoe = static_cast<unsigned>(y - era * 30);      // [0, 29]
+    auto const doy = 29*(m-1) + m/2 + d-1;                     // [0, 354]
+    auto const doe = yoe * 354 + (11*(yoe+1)+3)/30 + doy;      // [0, 10630]
+    return days{era * 10631 + static_cast<int>(doe) - 492148};
+}
+
+CONSTCD14
+inline
+year_month_day::operator sys_days() const NOEXCEPT
+{
+    return sys_days{to_days()};
+}
+
+CONSTCD14
+inline
+year_month_day::operator local_days() const NOEXCEPT
+{
+    return local_days{to_days()};
+}
+
+CONSTCD14
+inline
+bool
+year_month_day::ok() const NOEXCEPT
+{
+    if (!(y_.ok() && m_.ok()))
+        return false;
+    return 1_d <= d_ && d_ <= (y_/m_/last).day();
+}
+
+CONSTCD11
+inline
+bool
+operator==(const year_month_day& x, const year_month_day& y) NOEXCEPT
+{
+    return x.year() == y.year() && x.month() == y.month() && x.day() == y.day();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const year_month_day& x, const year_month_day& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+CONSTCD11
+inline
+bool
+operator<(const year_month_day& x, const year_month_day& y) NOEXCEPT
+{
+    return x.year() < y.year() ? true
+        : (x.year() > y.year() ? false
+        : (x.month() < y.month() ? true
+        : (x.month() > y.month() ? false
+        : (x.day() < y.day()))));
+}
+
+CONSTCD11
+inline
+bool
+operator>(const year_month_day& x, const year_month_day& y) NOEXCEPT
+{
+    return y < x;
+}
+
+CONSTCD11
+inline
+bool
+operator<=(const year_month_day& x, const year_month_day& y) NOEXCEPT
+{
+    return !(y < x);
+}
+
+CONSTCD11
+inline
+bool
+operator>=(const year_month_day& x, const year_month_day& y) NOEXCEPT
+{
+    return !(x < y);
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_month_day& ymd)
+{
+    date::detail::save_ostream<CharT, Traits> _(os);
+    os.fill('0');
+    os.flags(std::ios::dec | std::ios::right);
+    os << ymd.year() << '-';
+    os.width(2);
+    os << static_cast<unsigned>(ymd.month()) << '-';
+    os << ymd.day();
+    return os;
+}
+
+CONSTCD14
+inline
+year_month_day
+year_month_day::from_days(days dp) NOEXCEPT
+{
+    static_assert(std::numeric_limits<unsigned>::digits >= 18,
+             "This algorithm has not been ported to a 16 bit unsigned integer");
+    static_assert(std::numeric_limits<int>::digits >= 20,
+             "This algorithm has not been ported to a 16 bit signed integer");
+    auto const z = dp.count() + 492148;
+    auto const era = (z >= 0 ? z : z - 10630) / 10631;
+    auto const doe = static_cast<unsigned>(z - era * 10631);         // [0, 10630]
+    auto const yoe = (30*doe + 10646)/10631 - 1;                     // [0, 29]
+    auto const y = static_cast<sys_days::rep>(yoe) + era * 30 + 1;
+    auto const doy = doe - (yoe * 354 + (11*(yoe+1)+3)/30);          // [0, 354]
+    auto const m = (11*doy + 330) / 325;                             // [1, 12]
+    auto const d = doy - (29*(m-1) + m/2) + 1;                       // [1, 30]
+    return year_month_day{islamic::year{y}, islamic::month(m), islamic::day(d)};
+}
+
+CONSTCD14
+inline
+year_month_day
+operator+(const year_month_day& ymd, const months& dm) NOEXCEPT
+{
+    return (ymd.year() / ymd.month() + dm) / ymd.day();
+}
+
+CONSTCD14
+inline
+year_month_day
+operator+(const months& dm, const year_month_day& ymd) NOEXCEPT
+{
+    return ymd + dm;
+}
+
+CONSTCD14
+inline
+year_month_day
+operator-(const year_month_day& ymd, const months& dm) NOEXCEPT
+{
+    return ymd + (-dm);
+}
+
+CONSTCD11
+inline
+year_month_day
+operator+(const year_month_day& ymd, const years& dy) NOEXCEPT
+{
+    return (ymd.year() + dy) / ymd.month() / ymd.day();
+}
+
+CONSTCD11
+inline
+year_month_day
+operator+(const years& dy, const year_month_day& ymd) NOEXCEPT
+{
+    return ymd + dy;
+}
+
+CONSTCD11
+inline
+year_month_day
+operator-(const year_month_day& ymd, const years& dy) NOEXCEPT
+{
+    return ymd + (-dy);
+}
+
+// year_month_weekday
+
+CONSTCD11
+inline
+year_month_weekday::year_month_weekday(const islamic::year& y, const islamic::month& m,
+                                       const islamic::weekday_indexed& wdi)
+        NOEXCEPT
+    : y_(y)
+    , m_(m)
+    , wdi_(wdi)
+    {}
+
+CONSTCD14
+inline
+year_month_weekday::year_month_weekday(const sys_days& dp) NOEXCEPT
+    : year_month_weekday(from_days(dp.time_since_epoch()))
+    {}
+
+CONSTCD14
+inline
+year_month_weekday::year_month_weekday(const local_days& dp) NOEXCEPT
+    : year_month_weekday(from_days(dp.time_since_epoch()))
+    {}
+
+CONSTCD14
+inline
+year_month_weekday&
+year_month_weekday::operator+=(const months& m) NOEXCEPT
+{
+    *this = *this + m;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month_weekday&
+year_month_weekday::operator-=(const months& m) NOEXCEPT
+{
+    *this = *this - m;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month_weekday&
+year_month_weekday::operator+=(const years& y) NOEXCEPT
+{
+    *this = *this + y;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month_weekday&
+year_month_weekday::operator-=(const years& y) NOEXCEPT
+{
+    *this = *this - y;
+    return *this;
+}
+
+CONSTCD11 inline year year_month_weekday::year() const NOEXCEPT {return y_;}
+CONSTCD11 inline month year_month_weekday::month() const NOEXCEPT {return m_;}
+
+CONSTCD11
+inline
+weekday
+year_month_weekday::weekday() const NOEXCEPT
+{
+    return wdi_.weekday();
+}
+
+CONSTCD11
+inline
+unsigned
+year_month_weekday::index() const NOEXCEPT
+{
+    return wdi_.index();
+}
+
+CONSTCD11
+inline
+weekday_indexed
+year_month_weekday::weekday_indexed() const NOEXCEPT
+{
+    return wdi_;
+}
+
+CONSTCD14
+inline
+year_month_weekday::operator sys_days() const NOEXCEPT
+{
+    return sys_days{to_days()};
+}
+
+CONSTCD14
+inline
+year_month_weekday::operator local_days() const NOEXCEPT
+{
+    return local_days{to_days()};
+}
+
+CONSTCD14
+inline
+bool
+year_month_weekday::ok() const NOEXCEPT
+{
+    if (!y_.ok() || !m_.ok() || !wdi_.weekday().ok() || wdi_.index() < 1)
+        return false;
+    if (wdi_.index() <= 4)
+        return true;
+    auto d2 = wdi_.weekday() - islamic::weekday(y_/m_/1) + days((wdi_.index()-1)*7 + 1);
+    return static_cast<unsigned>(d2.count()) <= static_cast<unsigned>((y_/m_/last).day());
+}
+
+CONSTCD14
+inline
+year_month_weekday
+year_month_weekday::from_days(days d) NOEXCEPT
+{
+    sys_days dp{d};
+    auto const wd = islamic::weekday(dp);
+    auto const ymd = year_month_day(dp);
+    return {ymd.year(), ymd.month(), wd[(static_cast<unsigned>(ymd.day())-1)/7+1]};
+}
+
+CONSTCD14
+inline
+days
+year_month_weekday::to_days() const NOEXCEPT
+{
+    auto d = sys_days(y_/m_/1);
+    return (d + (wdi_.weekday() - islamic::weekday(d) + days{(wdi_.index()-1)*7})
+           ).time_since_epoch();
+}
+
+CONSTCD11
+inline
+bool
+operator==(const year_month_weekday& x, const year_month_weekday& y) NOEXCEPT
+{
+    return x.year() == y.year() && x.month() == y.month() &&
+           x.weekday_indexed() == y.weekday_indexed();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const year_month_weekday& x, const year_month_weekday& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_month_weekday& ymwdi)
+{
+    return os << ymwdi.year() << '/' << ymwdi.month()
+              << '/' << ymwdi.weekday_indexed();
+}
+
+CONSTCD14
+inline
+year_month_weekday
+operator+(const year_month_weekday& ymwd, const months& dm) NOEXCEPT
+{
+    return (ymwd.year() / ymwd.month() + dm) / ymwd.weekday_indexed();
+}
+
+CONSTCD14
+inline
+year_month_weekday
+operator+(const months& dm, const year_month_weekday& ymwd) NOEXCEPT
+{
+    return ymwd + dm;
+}
+
+CONSTCD14
+inline
+year_month_weekday
+operator-(const year_month_weekday& ymwd, const months& dm) NOEXCEPT
+{
+    return ymwd + (-dm);
+}
+
+CONSTCD11
+inline
+year_month_weekday
+operator+(const year_month_weekday& ymwd, const years& dy) NOEXCEPT
+{
+    return {ymwd.year()+dy, ymwd.month(), ymwd.weekday_indexed()};
+}
+
+CONSTCD11
+inline
+year_month_weekday
+operator+(const years& dy, const year_month_weekday& ymwd) NOEXCEPT
+{
+    return ymwd + dy;
+}
+
+CONSTCD11
+inline
+year_month_weekday
+operator-(const year_month_weekday& ymwd, const years& dy) NOEXCEPT
+{
+    return ymwd + (-dy);
+}
+
+// year_month_weekday_last
+
+CONSTCD11
+inline
+year_month_weekday_last::year_month_weekday_last(const islamic::year& y,
+                                                 const islamic::month& m,
+                                                 const islamic::weekday_last& wdl) NOEXCEPT
+    : y_(y)
+    , m_(m)
+    , wdl_(wdl)
+    {}
+
+CONSTCD14
+inline
+year_month_weekday_last&
+year_month_weekday_last::operator+=(const months& m) NOEXCEPT
+{
+    *this = *this + m;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month_weekday_last&
+year_month_weekday_last::operator-=(const months& m) NOEXCEPT
+{
+    *this = *this - m;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month_weekday_last&
+year_month_weekday_last::operator+=(const years& y) NOEXCEPT
+{
+    *this = *this + y;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month_weekday_last&
+year_month_weekday_last::operator-=(const years& y) NOEXCEPT
+{
+    *this = *this - y;
+    return *this;
+}
+
+CONSTCD11 inline year year_month_weekday_last::year() const NOEXCEPT {return y_;}
+CONSTCD11 inline month year_month_weekday_last::month() const NOEXCEPT {return m_;}
+
+CONSTCD11
+inline
+weekday
+year_month_weekday_last::weekday() const NOEXCEPT
+{
+    return wdl_.weekday();
+}
+
+CONSTCD11
+inline
+weekday_last
+year_month_weekday_last::weekday_last() const NOEXCEPT
+{
+    return wdl_;
+}
+
+CONSTCD14
+inline
+year_month_weekday_last::operator sys_days() const NOEXCEPT
+{
+    return sys_days{to_days()};
+}
+
+CONSTCD14
+inline
+year_month_weekday_last::operator local_days() const NOEXCEPT
+{
+    return local_days{to_days()};
+}
+
+CONSTCD11
+inline
+bool
+year_month_weekday_last::ok() const NOEXCEPT
+{
+    return y_.ok() && m_.ok() && wdl_.ok();
+}
+
+CONSTCD14
+inline
+days
+year_month_weekday_last::to_days() const NOEXCEPT
+{
+    auto const d = sys_days(y_/m_/last);
+    return (d - (islamic::weekday{d} - wdl_.weekday())).time_since_epoch();
+}
+
+CONSTCD11
+inline
+bool
+operator==(const year_month_weekday_last& x, const year_month_weekday_last& y) NOEXCEPT
+{
+    return x.year() == y.year() && x.month() == y.month() &&
+           x.weekday_last() == y.weekday_last();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const year_month_weekday_last& x, const year_month_weekday_last& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_month_weekday_last& ymwdl)
+{
+    return os << ymwdl.year() << '/' << ymwdl.month() << '/' << ymwdl.weekday_last();
+}
+
+CONSTCD14
+inline
+year_month_weekday_last
+operator+(const year_month_weekday_last& ymwdl, const months& dm) NOEXCEPT
+{
+    return (ymwdl.year() / ymwdl.month() + dm) / ymwdl.weekday_last();
+}
+
+CONSTCD14
+inline
+year_month_weekday_last
+operator+(const months& dm, const year_month_weekday_last& ymwdl) NOEXCEPT
+{
+    return ymwdl + dm;
+}
+
+CONSTCD14
+inline
+year_month_weekday_last
+operator-(const year_month_weekday_last& ymwdl, const months& dm) NOEXCEPT
+{
+    return ymwdl + (-dm);
+}
+
+CONSTCD11
+inline
+year_month_weekday_last
+operator+(const year_month_weekday_last& ymwdl, const years& dy) NOEXCEPT
+{
+    return {ymwdl.year()+dy, ymwdl.month(), ymwdl.weekday_last()};
+}
+
+CONSTCD11
+inline
+year_month_weekday_last
+operator+(const years& dy, const year_month_weekday_last& ymwdl) NOEXCEPT
+{
+    return ymwdl + dy;
+}
+
+CONSTCD11
+inline
+year_month_weekday_last
+operator-(const year_month_weekday_last& ymwdl, const years& dy) NOEXCEPT
+{
+    return ymwdl + (-dy);
+}
+
+// year_month from operator/()
+
+CONSTCD11
+inline
+year_month
+operator/(const year& y, const month& m) NOEXCEPT
+{
+    return {y, m};
+}
+
+CONSTCD11
+inline
+year_month
+operator/(const year& y, int   m) NOEXCEPT
+{
+    return y / month(static_cast<unsigned>(m));
+}
+
+// month_day from operator/()
+
+CONSTCD11
+inline
+month_day
+operator/(const month& m, const day& d) NOEXCEPT
+{
+    return {m, d};
+}
+
+CONSTCD11
+inline
+month_day
+operator/(const day& d, const month& m) NOEXCEPT
+{
+    return m / d;
+}
+
+CONSTCD11
+inline
+month_day
+operator/(const month& m, int d) NOEXCEPT
+{
+    return m / day(static_cast<unsigned>(d));
+}
+
+CONSTCD11
+inline
+month_day
+operator/(int m, const day& d) NOEXCEPT
+{
+    return month(static_cast<unsigned>(m)) / d;
+}
+
+CONSTCD11 inline month_day operator/(const day& d, int m) NOEXCEPT {return m / d;}
+
+// month_day_last from operator/()
+
+CONSTCD11
+inline
+month_day_last
+operator/(const month& m, last_spec) NOEXCEPT
+{
+    return month_day_last{m};
+}
+
+CONSTCD11
+inline
+month_day_last
+operator/(last_spec, const month& m) NOEXCEPT
+{
+    return m/last;
+}
+
+CONSTCD11
+inline
+month_day_last
+operator/(int m, last_spec) NOEXCEPT
+{
+    return month(static_cast<unsigned>(m))/last;
+}
+
+CONSTCD11
+inline
+month_day_last
+operator/(last_spec, int m) NOEXCEPT
+{
+    return m/last;
+}
+
+// month_weekday from operator/()
+
+CONSTCD11
+inline
+month_weekday
+operator/(const month& m, const weekday_indexed& wdi) NOEXCEPT
+{
+    return {m, wdi};
+}
+
+CONSTCD11
+inline
+month_weekday
+operator/(const weekday_indexed& wdi, const month& m) NOEXCEPT
+{
+    return m / wdi;
+}
+
+CONSTCD11
+inline
+month_weekday
+operator/(int m, const weekday_indexed& wdi) NOEXCEPT
+{
+    return month(static_cast<unsigned>(m)) / wdi;
+}
+
+CONSTCD11
+inline
+month_weekday
+operator/(const weekday_indexed& wdi, int m) NOEXCEPT
+{
+    return m / wdi;
+}
+
+// month_weekday_last from operator/()
+
+CONSTCD11
+inline
+month_weekday_last
+operator/(const month& m, const weekday_last& wdl) NOEXCEPT
+{
+    return {m, wdl};
+}
+
+CONSTCD11
+inline
+month_weekday_last
+operator/(const weekday_last& wdl, const month& m) NOEXCEPT
+{
+    return m / wdl;
+}
+
+CONSTCD11
+inline
+month_weekday_last
+operator/(int m, const weekday_last& wdl) NOEXCEPT
+{
+    return month(static_cast<unsigned>(m)) / wdl;
+}
+
+CONSTCD11
+inline
+month_weekday_last
+operator/(const weekday_last& wdl, int m) NOEXCEPT
+{
+    return m / wdl;
+}
+
+// year_month_day from operator/()
+
+CONSTCD11
+inline
+year_month_day
+operator/(const year_month& ym, const day& d) NOEXCEPT
+{
+    return {ym.year(), ym.month(), d};
+}
+
+CONSTCD11
+inline
+year_month_day
+operator/(const year_month& ym, int d)  NOEXCEPT
+{
+    return ym / day(static_cast<unsigned>(d));
+}
+
+CONSTCD11
+inline
+year_month_day
+operator/(const year& y, const month_day& md) NOEXCEPT
+{
+    return y / md.month() / md.day();
+}
+
+CONSTCD11
+inline
+year_month_day
+operator/(int y, const month_day& md) NOEXCEPT
+{
+    return year(y) / md;
+}
+
+CONSTCD11
+inline
+year_month_day
+operator/(const month_day& md, const year& y)  NOEXCEPT
+{
+    return y / md;
+}
+
+CONSTCD11
+inline
+year_month_day
+operator/(const month_day& md, int y) NOEXCEPT
+{
+    return year(y) / md;
+}
+
+// year_month_day_last from operator/()
+
+CONSTCD11
+inline
+year_month_day_last
+operator/(const year_month& ym, last_spec) NOEXCEPT
+{
+    return {ym.year(), month_day_last{ym.month()}};
+}
+
+CONSTCD11
+inline
+year_month_day_last
+operator/(const year& y, const month_day_last& mdl) NOEXCEPT
+{
+    return {y, mdl};
+}
+
+CONSTCD11
+inline
+year_month_day_last
+operator/(int y, const month_day_last& mdl) NOEXCEPT
+{
+    return year(y) / mdl;
+}
+
+CONSTCD11
+inline
+year_month_day_last
+operator/(const month_day_last& mdl, const year& y) NOEXCEPT
+{
+    return y / mdl;
+}
+
+CONSTCD11
+inline
+year_month_day_last
+operator/(const month_day_last& mdl, int y) NOEXCEPT
+{
+    return year(y) / mdl;
+}
+
+// year_month_weekday from operator/()
+
+CONSTCD11
+inline
+year_month_weekday
+operator/(const year_month& ym, const weekday_indexed& wdi) NOEXCEPT
+{
+    return {ym.year(), ym.month(), wdi};
+}
+
+CONSTCD11
+inline
+year_month_weekday
+operator/(const year& y, const month_weekday& mwd) NOEXCEPT
+{
+    return {y, mwd.month(), mwd.weekday_indexed()};
+}
+
+CONSTCD11
+inline
+year_month_weekday
+operator/(int y, const month_weekday& mwd) NOEXCEPT
+{
+    return year(y) / mwd;
+}
+
+CONSTCD11
+inline
+year_month_weekday
+operator/(const month_weekday& mwd, const year& y) NOEXCEPT
+{
+    return y / mwd;
+}
+
+CONSTCD11
+inline
+year_month_weekday
+operator/(const month_weekday& mwd, int y) NOEXCEPT
+{
+    return year(y) / mwd;
+}
+
+// year_month_weekday_last from operator/()
+
+CONSTCD11
+inline
+year_month_weekday_last
+operator/(const year_month& ym, const weekday_last& wdl) NOEXCEPT
+{
+    return {ym.year(), ym.month(), wdl};
+}
+
+CONSTCD11
+inline
+year_month_weekday_last
+operator/(const year& y, const month_weekday_last& mwdl) NOEXCEPT
+{
+    return {y, mwdl.month(), mwdl.weekday_last()};
+}
+
+CONSTCD11
+inline
+year_month_weekday_last
+operator/(int y, const month_weekday_last& mwdl) NOEXCEPT
+{
+    return year(y) / mwdl;
+}
+
+CONSTCD11
+inline
+year_month_weekday_last
+operator/(const month_weekday_last& mwdl, const year& y) NOEXCEPT
+{
+    return y / mwdl;
+}
+
+CONSTCD11
+inline
+year_month_weekday_last
+operator/(const month_weekday_last& mwdl, int y) NOEXCEPT
+{
+    return year(y) / mwdl;
+}
+
+}  // namespace islamic
+
+#endif  // ISLAMIC_H
diff --git a/third_party/date-3.0.1/include/date/iso_week.h b/third_party/date-3.0.1/include/date/iso_week.h
new file mode 100644
index 00000000..4a0a4a9b
--- /dev/null
+++ b/third_party/date-3.0.1/include/date/iso_week.h
@@ -0,0 +1,1751 @@
+#ifndef ISO_WEEK_H
+#define ISO_WEEK_H
+
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016, 2017 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+#include "date.h"
+
+#include <climits>
+
+namespace iso_week
+{
+
+// y/wn/wd
+// wn/wd/y
+// wd/wn/y
+
+using days = date::days;
+using weeks = date::weeks;
+using years = date::years;
+
+// time_point
+
+using sys_days = date::sys_days;
+using local_days = date::local_days;
+
+// types
+
+struct last_week
+{
+    explicit last_week() = default;
+};
+
+class weekday;
+class weeknum;
+class year;
+
+class year_weeknum;
+class year_lastweek;
+class weeknum_weekday;
+class lastweek_weekday;
+
+class year_weeknum_weekday;
+class year_lastweek_weekday;
+
+// date composition operators
+
+CONSTCD11 year_weeknum operator/(const year& y, const weeknum& wn) NOEXCEPT;
+CONSTCD11 year_weeknum operator/(const year& y, int            wn) NOEXCEPT;
+
+CONSTCD11 year_lastweek operator/(const year& y, last_week      wn) NOEXCEPT;
+
+CONSTCD11 weeknum_weekday operator/(const weeknum& wn, const weekday& wd) NOEXCEPT;
+CONSTCD11 weeknum_weekday operator/(const weeknum& wn, int            wd) NOEXCEPT;
+CONSTCD11 weeknum_weekday operator/(const weekday& wd, const weeknum& wn) NOEXCEPT;
+CONSTCD11 weeknum_weekday operator/(const weekday& wd, int            wn) NOEXCEPT;
+
+CONSTCD11 lastweek_weekday operator/(const last_week& wn, const weekday& wd) NOEXCEPT;
+CONSTCD11 lastweek_weekday operator/(const last_week& wn, int            wd) NOEXCEPT;
+CONSTCD11 lastweek_weekday operator/(const weekday& wd, const last_week& wn) NOEXCEPT;
+
+CONSTCD11 year_weeknum_weekday operator/(const year_weeknum& ywn, const weekday& wd) NOEXCEPT;
+CONSTCD11 year_weeknum_weekday operator/(const year_weeknum& ywn, int            wd) NOEXCEPT;
+CONSTCD11 year_weeknum_weekday operator/(const weeknum_weekday& wnwd, const year& y) NOEXCEPT;
+CONSTCD11 year_weeknum_weekday operator/(const weeknum_weekday& wnwd, int         y) NOEXCEPT;
+
+CONSTCD11 year_lastweek_weekday operator/(const year_lastweek& ylw, const weekday& wd) NOEXCEPT;
+CONSTCD11 year_lastweek_weekday operator/(const year_lastweek& ylw, int            wd) NOEXCEPT;
+
+CONSTCD11 year_lastweek_weekday operator/(const lastweek_weekday& lwwd, const year& y) NOEXCEPT;
+CONSTCD11 year_lastweek_weekday operator/(const lastweek_weekday& lwwd, int         y) NOEXCEPT;
+
+// weekday
+
+class weekday
+{
+    unsigned char wd_;
+public:
+    explicit CONSTCD11 weekday(unsigned wd) NOEXCEPT;
+    CONSTCD11 weekday(date::weekday wd) NOEXCEPT;
+    explicit weekday(int) = delete;
+    CONSTCD11 weekday(const sys_days& dp) NOEXCEPT;
+    CONSTCD11 explicit weekday(const local_days& dp) NOEXCEPT;
+
+    weekday& operator++()    NOEXCEPT;
+    weekday  operator++(int) NOEXCEPT;
+    weekday& operator--()    NOEXCEPT;
+    weekday  operator--(int) NOEXCEPT;
+
+    weekday& operator+=(const days& d) NOEXCEPT;
+    weekday& operator-=(const days& d) NOEXCEPT;
+
+    CONSTCD11 explicit operator unsigned() const NOEXCEPT;
+    CONSTCD11 operator date::weekday() const NOEXCEPT;
+    CONSTCD11 bool ok() const NOEXCEPT;
+
+private:
+    static CONSTCD11 unsigned char weekday_from_days(int z) NOEXCEPT;
+    static CONSTCD11 unsigned char to_iso_encoding(unsigned char) NOEXCEPT;
+    static CONSTCD11 unsigned from_iso_encoding(unsigned) NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const weekday& x, const weekday& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const weekday& x, const weekday& y) NOEXCEPT;
+
+CONSTCD14 weekday operator+(const weekday& x, const days&    y) NOEXCEPT;
+CONSTCD14 weekday operator+(const days&    x, const weekday& y) NOEXCEPT;
+CONSTCD14 weekday operator-(const weekday& x, const days&    y) NOEXCEPT;
+CONSTCD14 days    operator-(const weekday& x, const weekday& y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const weekday& wd);
+
+// year
+
+class year
+{
+    short y_;
+
+public:
+    explicit CONSTCD11 year(int y) NOEXCEPT;
+
+    year& operator++()    NOEXCEPT;
+    year  operator++(int) NOEXCEPT;
+    year& operator--()    NOEXCEPT;
+    year  operator--(int) NOEXCEPT;
+
+    year& operator+=(const years& y) NOEXCEPT;
+    year& operator-=(const years& y) NOEXCEPT;
+
+    CONSTCD11 explicit operator int() const NOEXCEPT;
+    CONSTCD11 bool ok() const NOEXCEPT;
+
+    static CONSTCD11 year min() NOEXCEPT;
+    static CONSTCD11 year max() NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const year& x, const year& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const year& x, const year& y) NOEXCEPT;
+CONSTCD11 bool operator< (const year& x, const year& y) NOEXCEPT;
+CONSTCD11 bool operator> (const year& x, const year& y) NOEXCEPT;
+CONSTCD11 bool operator<=(const year& x, const year& y) NOEXCEPT;
+CONSTCD11 bool operator>=(const year& x, const year& y) NOEXCEPT;
+
+CONSTCD11 year  operator+(const year&  x, const years& y) NOEXCEPT;
+CONSTCD11 year  operator+(const years& x, const year&  y) NOEXCEPT;
+CONSTCD11 year  operator-(const year&  x, const years& y) NOEXCEPT;
+CONSTCD11 years operator-(const year&  x, const year&  y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year& y);
+
+// weeknum
+
+class weeknum
+{
+    unsigned char wn_;
+
+public:
+    explicit CONSTCD11 weeknum(unsigned wn) NOEXCEPT;
+
+    weeknum& operator++()    NOEXCEPT;
+    weeknum  operator++(int) NOEXCEPT;
+    weeknum& operator--()    NOEXCEPT;
+    weeknum  operator--(int) NOEXCEPT;
+
+    weeknum& operator+=(const weeks& y) NOEXCEPT;
+    weeknum& operator-=(const weeks& y) NOEXCEPT;
+
+    CONSTCD11 explicit operator unsigned() const NOEXCEPT;
+    CONSTCD11 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const weeknum& x, const weeknum& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const weeknum& x, const weeknum& y) NOEXCEPT;
+CONSTCD11 bool operator< (const weeknum& x, const weeknum& y) NOEXCEPT;
+CONSTCD11 bool operator> (const weeknum& x, const weeknum& y) NOEXCEPT;
+CONSTCD11 bool operator<=(const weeknum& x, const weeknum& y) NOEXCEPT;
+CONSTCD11 bool operator>=(const weeknum& x, const weeknum& y) NOEXCEPT;
+
+CONSTCD11 weeknum  operator+(const weeknum& x, const weeks&   y) NOEXCEPT;
+CONSTCD11 weeknum  operator+(const weeks&   x, const weeknum& y) NOEXCEPT;
+CONSTCD11 weeknum  operator-(const weeknum& x, const weeks&   y) NOEXCEPT;
+CONSTCD11 weeks    operator-(const weeknum& x, const weeknum& y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const weeknum& wn);
+
+// year_weeknum
+
+class year_weeknum
+{
+    iso_week::year    y_;
+    iso_week::weeknum wn_;
+
+public:
+    CONSTCD11 year_weeknum(const iso_week::year& y, const iso_week::weeknum& wn) NOEXCEPT;
+
+    CONSTCD11 iso_week::year    year()    const NOEXCEPT;
+    CONSTCD11 iso_week::weeknum weeknum() const NOEXCEPT;
+
+    year_weeknum& operator+=(const years& dy) NOEXCEPT;
+    year_weeknum& operator-=(const years& dy) NOEXCEPT;
+
+    CONSTCD11 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const year_weeknum& x, const year_weeknum& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const year_weeknum& x, const year_weeknum& y) NOEXCEPT;
+CONSTCD11 bool operator< (const year_weeknum& x, const year_weeknum& y) NOEXCEPT;
+CONSTCD11 bool operator> (const year_weeknum& x, const year_weeknum& y) NOEXCEPT;
+CONSTCD11 bool operator<=(const year_weeknum& x, const year_weeknum& y) NOEXCEPT;
+CONSTCD11 bool operator>=(const year_weeknum& x, const year_weeknum& y) NOEXCEPT;
+
+CONSTCD11 year_weeknum operator+(const year_weeknum& ym, const years& dy) NOEXCEPT;
+CONSTCD11 year_weeknum operator+(const years& dy, const year_weeknum& ym) NOEXCEPT;
+CONSTCD11 year_weeknum operator-(const year_weeknum& ym, const years& dy) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_weeknum& ym);
+
+// year_lastweek
+
+class year_lastweek
+{
+    iso_week::year    y_;
+
+public:
+    CONSTCD11 explicit year_lastweek(const iso_week::year& y) NOEXCEPT;
+
+    CONSTCD11 iso_week::year    year()    const NOEXCEPT;
+    CONSTCD14 iso_week::weeknum weeknum() const NOEXCEPT;
+
+    year_lastweek& operator+=(const years& dy) NOEXCEPT;
+    year_lastweek& operator-=(const years& dy) NOEXCEPT;
+
+    CONSTCD11 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const year_lastweek& x, const year_lastweek& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const year_lastweek& x, const year_lastweek& y) NOEXCEPT;
+CONSTCD11 bool operator< (const year_lastweek& x, const year_lastweek& y) NOEXCEPT;
+CONSTCD11 bool operator> (const year_lastweek& x, const year_lastweek& y) NOEXCEPT;
+CONSTCD11 bool operator<=(const year_lastweek& x, const year_lastweek& y) NOEXCEPT;
+CONSTCD11 bool operator>=(const year_lastweek& x, const year_lastweek& y) NOEXCEPT;
+
+CONSTCD11 year_lastweek operator+(const year_lastweek& ym, const years& dy) NOEXCEPT;
+CONSTCD11 year_lastweek operator+(const years& dy, const year_lastweek& ym) NOEXCEPT;
+CONSTCD11 year_lastweek operator-(const year_lastweek& ym, const years& dy) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_lastweek& ym);
+
+// weeknum_weekday
+
+class weeknum_weekday
+{
+    iso_week::weeknum wn_;
+    iso_week::weekday wd_;
+
+public:
+    CONSTCD11 weeknum_weekday(const iso_week::weeknum& wn,
+                              const iso_week::weekday& wd) NOEXCEPT;
+
+    CONSTCD11 iso_week::weeknum weeknum() const NOEXCEPT;
+    CONSTCD11 iso_week::weekday weekday() const NOEXCEPT;
+
+    CONSTCD14 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const weeknum_weekday& x, const weeknum_weekday& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const weeknum_weekday& x, const weeknum_weekday& y) NOEXCEPT;
+CONSTCD11 bool operator< (const weeknum_weekday& x, const weeknum_weekday& y) NOEXCEPT;
+CONSTCD11 bool operator> (const weeknum_weekday& x, const weeknum_weekday& y) NOEXCEPT;
+CONSTCD11 bool operator<=(const weeknum_weekday& x, const weeknum_weekday& y) NOEXCEPT;
+CONSTCD11 bool operator>=(const weeknum_weekday& x, const weeknum_weekday& y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const weeknum_weekday& md);
+
+// lastweek_weekday
+
+class lastweek_weekday
+{
+    iso_week::weekday wd_;
+
+public:
+    CONSTCD11 explicit lastweek_weekday(const iso_week::weekday& wd) NOEXCEPT;
+
+    CONSTCD11 iso_week::weekday weekday() const NOEXCEPT;
+
+    CONSTCD14 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const lastweek_weekday& x, const lastweek_weekday& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const lastweek_weekday& x, const lastweek_weekday& y) NOEXCEPT;
+CONSTCD11 bool operator< (const lastweek_weekday& x, const lastweek_weekday& y) NOEXCEPT;
+CONSTCD11 bool operator> (const lastweek_weekday& x, const lastweek_weekday& y) NOEXCEPT;
+CONSTCD11 bool operator<=(const lastweek_weekday& x, const lastweek_weekday& y) NOEXCEPT;
+CONSTCD11 bool operator>=(const lastweek_weekday& x, const lastweek_weekday& y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const lastweek_weekday& md);
+
+// year_lastweek_weekday
+
+class year_lastweek_weekday
+{
+    iso_week::year    y_;
+    iso_week::weekday wd_;
+
+public:
+    CONSTCD11 year_lastweek_weekday(const iso_week::year& y,
+                                    const iso_week::weekday& wd) NOEXCEPT;
+
+    year_lastweek_weekday& operator+=(const years& y) NOEXCEPT;
+    year_lastweek_weekday& operator-=(const years& y) NOEXCEPT;
+
+    CONSTCD11 iso_week::year    year()    const NOEXCEPT;
+    CONSTCD14 iso_week::weeknum weeknum() const NOEXCEPT;
+    CONSTCD11 iso_week::weekday weekday() const NOEXCEPT;
+
+    CONSTCD14 operator sys_days() const NOEXCEPT;
+    CONSTCD14 explicit operator local_days() const NOEXCEPT;
+    CONSTCD11 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const year_lastweek_weekday& x, const year_lastweek_weekday& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const year_lastweek_weekday& x, const year_lastweek_weekday& y) NOEXCEPT;
+CONSTCD11 bool operator< (const year_lastweek_weekday& x, const year_lastweek_weekday& y) NOEXCEPT;
+CONSTCD11 bool operator> (const year_lastweek_weekday& x, const year_lastweek_weekday& y) NOEXCEPT;
+CONSTCD11 bool operator<=(const year_lastweek_weekday& x, const year_lastweek_weekday& y) NOEXCEPT;
+CONSTCD11 bool operator>=(const year_lastweek_weekday& x, const year_lastweek_weekday& y) NOEXCEPT;
+
+CONSTCD11 year_lastweek_weekday operator+(const year_lastweek_weekday& ywnwd, const years& y) NOEXCEPT;
+CONSTCD11 year_lastweek_weekday operator+(const years& y, const year_lastweek_weekday& ywnwd) NOEXCEPT;
+CONSTCD11 year_lastweek_weekday operator-(const year_lastweek_weekday& ywnwd, const years& y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_lastweek_weekday& ywnwd);
+
+// class year_weeknum_weekday
+
+class year_weeknum_weekday
+{
+    iso_week::year    y_;
+    iso_week::weeknum wn_;
+    iso_week::weekday wd_;
+
+public:
+    CONSTCD11 year_weeknum_weekday(const iso_week::year& y, const iso_week::weeknum& wn,
+                                   const iso_week::weekday& wd) NOEXCEPT;
+    CONSTCD14 year_weeknum_weekday(const year_lastweek_weekday& ylwwd) NOEXCEPT;
+    CONSTCD14 year_weeknum_weekday(const sys_days& dp) NOEXCEPT;
+    CONSTCD14 explicit year_weeknum_weekday(const local_days& dp) NOEXCEPT;
+
+    year_weeknum_weekday& operator+=(const years& y) NOEXCEPT;
+    year_weeknum_weekday& operator-=(const years& y) NOEXCEPT;
+
+    CONSTCD11 iso_week::year    year()    const NOEXCEPT;
+    CONSTCD11 iso_week::weeknum weeknum() const NOEXCEPT;
+    CONSTCD11 iso_week::weekday weekday() const NOEXCEPT;
+
+    CONSTCD14 operator sys_days() const NOEXCEPT;
+    CONSTCD14 explicit operator local_days() const NOEXCEPT;
+    CONSTCD14 bool ok() const NOEXCEPT;
+
+private:
+    static CONSTCD14 year_weeknum_weekday from_days(days dp) NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const year_weeknum_weekday& x, const year_weeknum_weekday& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const year_weeknum_weekday& x, const year_weeknum_weekday& y) NOEXCEPT;
+CONSTCD11 bool operator< (const year_weeknum_weekday& x, const year_weeknum_weekday& y) NOEXCEPT;
+CONSTCD11 bool operator> (const year_weeknum_weekday& x, const year_weeknum_weekday& y) NOEXCEPT;
+CONSTCD11 bool operator<=(const year_weeknum_weekday& x, const year_weeknum_weekday& y) NOEXCEPT;
+CONSTCD11 bool operator>=(const year_weeknum_weekday& x, const year_weeknum_weekday& y) NOEXCEPT;
+
+CONSTCD11 year_weeknum_weekday operator+(const year_weeknum_weekday& ywnwd, const years& y) NOEXCEPT;
+CONSTCD11 year_weeknum_weekday operator+(const years& y, const year_weeknum_weekday& ywnwd) NOEXCEPT;
+CONSTCD11 year_weeknum_weekday operator-(const year_weeknum_weekday& ywnwd, const years& y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_weeknum_weekday& ywnwd);
+
+//----------------+
+// Implementation |
+//----------------+
+
+// weekday
+
+CONSTCD11
+inline
+unsigned char
+weekday::to_iso_encoding(unsigned char z) NOEXCEPT
+{
+    return z != 0 ? z : (unsigned char)7;
+}
+
+CONSTCD11
+inline
+unsigned
+weekday::from_iso_encoding(unsigned z) NOEXCEPT
+{
+    return z != 7 ? z : 0u;
+}
+
+CONSTCD11
+inline
+unsigned char
+weekday::weekday_from_days(int z) NOEXCEPT
+{
+    return to_iso_encoding(static_cast<unsigned char>(static_cast<unsigned>(
+        z >= -4 ? (z+4) % 7 : (z+5) % 7 + 6)));
+}
+
+CONSTCD11
+inline
+weekday::weekday(unsigned wd) NOEXCEPT
+    : wd_(static_cast<decltype(wd_)>(wd))
+    {}
+
+CONSTCD11
+inline
+weekday::weekday(date::weekday wd) NOEXCEPT
+    : wd_(wd.iso_encoding())
+    {}
+
+CONSTCD11
+inline
+weekday::weekday(const sys_days& dp) NOEXCEPT
+    : wd_(weekday_from_days(dp.time_since_epoch().count()))
+    {}
+
+CONSTCD11
+inline
+weekday::weekday(const local_days& dp) NOEXCEPT
+    : wd_(weekday_from_days(dp.time_since_epoch().count()))
+    {}
+
+inline weekday& weekday::operator++() NOEXCEPT {if (++wd_ == 8) wd_ = 1; return *this;}
+inline weekday weekday::operator++(int) NOEXCEPT {auto tmp(*this); ++(*this); return tmp;}
+inline weekday& weekday::operator--() NOEXCEPT {if (wd_-- == 1) wd_ = 7; return *this;}
+inline weekday weekday::operator--(int) NOEXCEPT {auto tmp(*this); --(*this); return tmp;}
+
+inline
+weekday&
+weekday::operator+=(const days& d) NOEXCEPT
+{
+    *this = *this + d;
+    return *this;
+}
+
+inline
+weekday&
+weekday::operator-=(const days& d) NOEXCEPT
+{
+    *this = *this - d;
+    return *this;
+}
+
+CONSTCD11
+inline
+weekday::operator unsigned() const NOEXCEPT
+{
+    return wd_;
+}
+
+CONSTCD11
+inline
+weekday::operator date::weekday() const NOEXCEPT
+{
+    return date::weekday{from_iso_encoding(unsigned{wd_})};
+}
+
+CONSTCD11 inline bool weekday::ok() const NOEXCEPT {return 1 <= wd_ && wd_ <= 7;}
+
+CONSTCD11
+inline
+bool
+operator==(const weekday& x, const weekday& y) NOEXCEPT
+{
+    return static_cast<unsigned>(x) == static_cast<unsigned>(y);
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const weekday& x, const weekday& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+CONSTCD14
+inline
+days
+operator-(const weekday& x, const weekday& y) NOEXCEPT
+{
+    auto const diff = static_cast<unsigned>(x) - static_cast<unsigned>(y);
+    return days{diff <= 6 ? diff : diff + 7};
+}
+
+CONSTCD14
+inline
+weekday
+operator+(const weekday& x, const days& y) NOEXCEPT
+{
+    auto const wdu = static_cast<long long>(static_cast<unsigned>(x) - 1u) + y.count();
+    auto const wk = (wdu >= 0 ? wdu : wdu-6) / 7;
+    return weekday{static_cast<unsigned>(wdu - wk * 7) + 1u};
+}
+
+CONSTCD14
+inline
+weekday
+operator+(const days& x, const weekday& y) NOEXCEPT
+{
+    return y + x;
+}
+
+CONSTCD14
+inline
+weekday
+operator-(const weekday& x, const days& y) NOEXCEPT
+{
+    return x + -y;
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const weekday& wd)
+{
+    switch (static_cast<unsigned>(wd))
+    {
+    case 7:
+        os << "Sun";
+        break;
+    case 1:
+        os << "Mon";
+        break;
+    case 2:
+        os << "Tue";
+        break;
+    case 3:
+        os << "Wed";
+        break;
+    case 4:
+        os << "Thu";
+        break;
+    case 5:
+        os << "Fri";
+        break;
+    case 6:
+        os << "Sat";
+        break;
+    default:
+        os << static_cast<unsigned>(wd) << " is not a valid weekday";
+        break;
+    }
+    return os;
+}
+
+// year
+
+CONSTCD11 inline year::year(int y) NOEXCEPT : y_(static_cast<decltype(y_)>(y)) {}
+inline year& year::operator++() NOEXCEPT {++y_; return *this;}
+inline year year::operator++(int) NOEXCEPT {auto tmp(*this); ++(*this); return tmp;}
+inline year& year::operator--() NOEXCEPT {--y_; return *this;}
+inline year year::operator--(int) NOEXCEPT {auto tmp(*this); --(*this); return tmp;}
+inline year& year::operator+=(const years& y) NOEXCEPT {*this = *this + y; return *this;}
+inline year& year::operator-=(const years& y) NOEXCEPT {*this = *this - y; return *this;}
+
+CONSTCD11 inline year::operator int() const NOEXCEPT {return y_;}
+CONSTCD11 inline bool year::ok() const NOEXCEPT {return min() <= *this && *this <= max();}
+
+CONSTCD11
+inline
+year
+year::min() NOEXCEPT
+{
+    using std::chrono::seconds;
+    using std::chrono::minutes;
+    using std::chrono::hours;
+    using std::chrono::duration_cast;
+    static_assert(sizeof(seconds)*CHAR_BIT >= 41, "seconds may overflow");
+    static_assert(sizeof(hours)*CHAR_BIT >= 30, "hours may overflow");
+    return sizeof(minutes)*CHAR_BIT < 34 ?
+        year{1970} + duration_cast<years>(minutes::min()) :
+        year{std::numeric_limits<short>::min()};
+}
+
+CONSTCD11
+inline
+year
+year::max() NOEXCEPT
+{
+    using std::chrono::seconds;
+    using std::chrono::minutes;
+    using std::chrono::hours;
+    using std::chrono::duration_cast;
+    static_assert(sizeof(seconds)*CHAR_BIT >= 41, "seconds may overflow");
+    static_assert(sizeof(hours)*CHAR_BIT >= 30, "hours may overflow");
+    return sizeof(minutes)*CHAR_BIT < 34 ?
+        year{1969} + duration_cast<years>(minutes::max()) :
+        year{std::numeric_limits<short>::max()};
+}
+
+CONSTCD11
+inline
+bool
+operator==(const year& x, const year& y) NOEXCEPT
+{
+    return static_cast<int>(x) == static_cast<int>(y);
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const year& x, const year& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+CONSTCD11
+inline
+bool
+operator<(const year& x, const year& y) NOEXCEPT
+{
+    return static_cast<int>(x) < static_cast<int>(y);
+}
+
+CONSTCD11
+inline
+bool
+operator>(const year& x, const year& y) NOEXCEPT
+{
+    return y < x;
+}
+
+CONSTCD11
+inline
+bool
+operator<=(const year& x, const year& y) NOEXCEPT
+{
+    return !(y < x);
+}
+
+CONSTCD11
+inline
+bool
+operator>=(const year& x, const year& y) NOEXCEPT
+{
+    return !(x < y);
+}
+
+CONSTCD11
+inline
+years
+operator-(const year& x, const year& y) NOEXCEPT
+{
+    return years{static_cast<int>(x) - static_cast<int>(y)};
+}
+
+CONSTCD11
+inline
+year
+operator+(const year& x, const years& y) NOEXCEPT
+{
+    return year{static_cast<int>(x) + y.count()};
+}
+
+CONSTCD11
+inline
+year
+operator+(const years& x, const year& y) NOEXCEPT
+{
+    return y + x;
+}
+
+CONSTCD11
+inline
+year
+operator-(const year& x, const years& y) NOEXCEPT
+{
+    return year{static_cast<int>(x) - y.count()};
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year& y)
+{
+    date::detail::save_ostream<CharT, Traits> _(os);
+    os.fill('0');
+    os.flags(std::ios::dec | std::ios::internal);
+    os.width(4 + (y < year{0}));
+    os << static_cast<int>(y);
+    return os;
+}
+
+#if !defined(_MSC_VER) || (_MSC_VER >= 1900)
+inline namespace literals
+{
+
+CONSTCD11
+inline
+iso_week::year
+operator "" _y(unsigned long long y) NOEXCEPT
+{
+    return iso_week::year(static_cast<int>(y));
+}
+
+CONSTCD11
+inline
+iso_week::weeknum
+operator "" _w(unsigned long long wn) NOEXCEPT
+{
+    return iso_week::weeknum(static_cast<unsigned>(wn));
+}
+
+#endif  // !defined(_MSC_VER) || (_MSC_VER >= 1900)
+
+CONSTDATA iso_week::last_week last{};
+
+CONSTDATA iso_week::weekday sun{7u};
+CONSTDATA iso_week::weekday mon{1u};
+CONSTDATA iso_week::weekday tue{2u};
+CONSTDATA iso_week::weekday wed{3u};
+CONSTDATA iso_week::weekday thu{4u};
+CONSTDATA iso_week::weekday fri{5u};
+CONSTDATA iso_week::weekday sat{6u};
+
+#if !defined(_MSC_VER) || (_MSC_VER >= 1900)
+}  // inline namespace literals
+#endif
+
+// weeknum
+
+CONSTCD11
+inline
+weeknum::weeknum(unsigned wn) NOEXCEPT
+    : wn_(static_cast<decltype(wn_)>(wn))
+    {}
+
+inline weeknum& weeknum::operator++() NOEXCEPT {++wn_; return *this;}
+inline weeknum weeknum::operator++(int) NOEXCEPT {auto tmp(*this); ++(*this); return tmp;}
+inline weeknum& weeknum::operator--() NOEXCEPT {--wn_; return *this;}
+inline weeknum weeknum::operator--(int) NOEXCEPT {auto tmp(*this); --(*this); return tmp;}
+
+inline
+weeknum&
+weeknum::operator+=(const weeks& y) NOEXCEPT
+{
+    *this = *this + y;
+    return *this;
+}
+
+inline
+weeknum&
+weeknum::operator-=(const weeks& y) NOEXCEPT
+{
+    *this = *this - y;
+    return *this;
+}
+
+CONSTCD11 inline weeknum::operator unsigned() const NOEXCEPT {return wn_;}
+CONSTCD11 inline bool weeknum::ok() const NOEXCEPT {return 1 <= wn_ && wn_ <= 53;}
+
+CONSTCD11
+inline
+bool
+operator==(const weeknum& x, const weeknum& y) NOEXCEPT
+{
+    return static_cast<unsigned>(x) == static_cast<unsigned>(y);
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const weeknum& x, const weeknum& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+CONSTCD11
+inline
+bool
+operator<(const weeknum& x, const weeknum& y) NOEXCEPT
+{
+    return static_cast<unsigned>(x) < static_cast<unsigned>(y);
+}
+
+CONSTCD11
+inline
+bool
+operator>(const weeknum& x, const weeknum& y) NOEXCEPT
+{
+    return y < x;
+}
+
+CONSTCD11
+inline
+bool
+operator<=(const weeknum& x, const weeknum& y) NOEXCEPT
+{
+    return !(y < x);
+}
+
+CONSTCD11
+inline
+bool
+operator>=(const weeknum& x, const weeknum& y) NOEXCEPT
+{
+    return !(x < y);
+}
+
+CONSTCD11
+inline
+weeks
+operator-(const weeknum& x, const weeknum& y) NOEXCEPT
+{
+    return weeks{static_cast<weeks::rep>(static_cast<unsigned>(x)) -
+                 static_cast<weeks::rep>(static_cast<unsigned>(y))};
+}
+
+CONSTCD11
+inline
+weeknum
+operator+(const weeknum& x, const weeks& y) NOEXCEPT
+{
+    return weeknum{static_cast<unsigned>(x) + static_cast<unsigned>(y.count())};
+}
+
+CONSTCD11
+inline
+weeknum
+operator+(const weeks& x, const weeknum& y) NOEXCEPT
+{
+    return y + x;
+}
+
+CONSTCD11
+inline
+weeknum
+operator-(const weeknum& x, const weeks& y) NOEXCEPT
+{
+    return x + -y;
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const weeknum& wn)
+{
+    date::detail::save_ostream<CharT, Traits> _(os);
+    os << 'W';
+    os.fill('0');
+    os.flags(std::ios::dec | std::ios::right);
+    os.width(2);
+    os << static_cast<unsigned>(wn);
+    return os;
+}
+
+// year_weeknum
+
+CONSTCD11
+inline
+year_weeknum::year_weeknum(const iso_week::year& y, const iso_week::weeknum& wn) NOEXCEPT
+    : y_(y)
+    , wn_(wn)
+    {}
+
+CONSTCD11 inline year year_weeknum::year() const NOEXCEPT {return y_;}
+CONSTCD11 inline weeknum year_weeknum::weeknum() const NOEXCEPT {return wn_;}
+CONSTCD11 inline bool year_weeknum::ok() const NOEXCEPT
+{
+    return y_.ok() && 1u <= static_cast<unsigned>(wn_) && wn_ <= (y_/last).weeknum();
+}
+
+inline
+year_weeknum&
+year_weeknum::operator+=(const years& dy) NOEXCEPT
+{
+    *this = *this + dy;
+    return *this;
+}
+
+inline
+year_weeknum&
+year_weeknum::operator-=(const years& dy) NOEXCEPT
+{
+    *this = *this - dy;
+    return *this;
+}
+
+CONSTCD11
+inline
+bool
+operator==(const year_weeknum& x, const year_weeknum& y) NOEXCEPT
+{
+    return x.year() == y.year() && x.weeknum() == y.weeknum();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const year_weeknum& x, const year_weeknum& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+CONSTCD11
+inline
+bool
+operator<(const year_weeknum& x, const year_weeknum& y) NOEXCEPT
+{
+    return x.year() < y.year() ? true
+        : (x.year() > y.year() ? false
+        : (x.weeknum() < y.weeknum()));
+}
+
+CONSTCD11
+inline
+bool
+operator>(const year_weeknum& x, const year_weeknum& y) NOEXCEPT
+{
+    return y < x;
+}
+
+CONSTCD11
+inline
+bool
+operator<=(const year_weeknum& x, const year_weeknum& y) NOEXCEPT
+{
+    return !(y < x);
+}
+
+CONSTCD11
+inline
+bool
+operator>=(const year_weeknum& x, const year_weeknum& y) NOEXCEPT
+{
+    return !(x < y);
+}
+
+CONSTCD11
+inline
+year_weeknum
+operator+(const year_weeknum& ym, const years& dy) NOEXCEPT
+{
+    return (ym.year() + dy) / ym.weeknum();
+}
+
+CONSTCD11
+inline
+year_weeknum
+operator+(const years& dy, const year_weeknum& ym) NOEXCEPT
+{
+    return ym + dy;
+}
+
+CONSTCD11
+inline
+year_weeknum
+operator-(const year_weeknum& ym, const years& dy) NOEXCEPT
+{
+    return ym + -dy;
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_weeknum& ywn)
+{
+    return os << ywn.year() << '-' << ywn.weeknum();
+}
+
+
+// year_lastweek
+
+CONSTCD11
+inline
+year_lastweek::year_lastweek(const iso_week::year& y) NOEXCEPT
+    : y_(y)
+    {}
+
+CONSTCD11 inline year year_lastweek::year() const NOEXCEPT {return y_;}
+
+CONSTCD14
+inline
+weeknum
+year_lastweek::weeknum() const NOEXCEPT
+{
+    const auto y = date::year{static_cast<int>(y_)};
+    const auto s0 = sys_days((y-years{1})/12/date::thu[date::last]);
+    const auto s1 = sys_days(y/12/date::thu[date::last]);
+    return iso_week::weeknum(static_cast<unsigned>(date::trunc<weeks>(s1-s0).count()));
+}
+
+CONSTCD11 inline bool year_lastweek::ok() const NOEXCEPT {return y_.ok();}
+
+inline
+year_lastweek&
+year_lastweek::operator+=(const years& dy) NOEXCEPT
+{
+    *this = *this + dy;
+    return *this;
+}
+
+inline
+year_lastweek&
+year_lastweek::operator-=(const years& dy) NOEXCEPT
+{
+    *this = *this - dy;
+    return *this;
+}
+
+CONSTCD11
+inline
+bool
+operator==(const year_lastweek& x, const year_lastweek& y) NOEXCEPT
+{
+    return x.year() == y.year();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const year_lastweek& x, const year_lastweek& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+CONSTCD11
+inline
+bool
+operator<(const year_lastweek& x, const year_lastweek& y) NOEXCEPT
+{
+    return x.year() < y.year();
+}
+
+CONSTCD11
+inline
+bool
+operator>(const year_lastweek& x, const year_lastweek& y) NOEXCEPT
+{
+    return y < x;
+}
+
+CONSTCD11
+inline
+bool
+operator<=(const year_lastweek& x, const year_lastweek& y) NOEXCEPT
+{
+    return !(y < x);
+}
+
+CONSTCD11
+inline
+bool
+operator>=(const year_lastweek& x, const year_lastweek& y) NOEXCEPT
+{
+    return !(x < y);
+}
+
+CONSTCD11
+inline
+year_lastweek
+operator+(const year_lastweek& ym, const years& dy) NOEXCEPT
+{
+    return year_lastweek{ym.year() + dy};
+}
+
+CONSTCD11
+inline
+year_lastweek
+operator+(const years& dy, const year_lastweek& ym) NOEXCEPT
+{
+    return ym + dy;
+}
+
+CONSTCD11
+inline
+year_lastweek
+operator-(const year_lastweek& ym, const years& dy) NOEXCEPT
+{
+    return ym + -dy;
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_lastweek& ywn)
+{
+    return os << ywn.year() << "-W last";
+}
+
+// weeknum_weekday
+
+CONSTCD11
+inline
+weeknum_weekday::weeknum_weekday(const iso_week::weeknum& wn,
+                                 const iso_week::weekday& wd) NOEXCEPT
+    : wn_(wn)
+    , wd_(wd)
+    {}
+
+CONSTCD11 inline weeknum weeknum_weekday::weeknum() const NOEXCEPT {return wn_;}
+CONSTCD11 inline weekday weeknum_weekday::weekday() const NOEXCEPT {return wd_;}
+
+CONSTCD14
+inline
+bool
+weeknum_weekday::ok() const NOEXCEPT
+{
+    return wn_.ok() && wd_.ok();
+}
+
+CONSTCD11
+inline
+bool
+operator==(const weeknum_weekday& x, const weeknum_weekday& y) NOEXCEPT
+{
+    return x.weeknum() == y.weeknum() && x.weekday() == y.weekday();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const weeknum_weekday& x, const weeknum_weekday& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+CONSTCD11
+inline
+bool
+operator<(const weeknum_weekday& x, const weeknum_weekday& y) NOEXCEPT
+{
+    return x.weeknum() < y.weeknum() ? true
+        : (x.weeknum() > y.weeknum() ? false
+        : (static_cast<unsigned>(x.weekday()) < static_cast<unsigned>(y.weekday())));
+}
+
+CONSTCD11
+inline
+bool
+operator>(const weeknum_weekday& x, const weeknum_weekday& y) NOEXCEPT
+{
+    return y < x;
+}
+
+CONSTCD11
+inline
+bool
+operator<=(const weeknum_weekday& x, const weeknum_weekday& y) NOEXCEPT
+{
+    return !(y < x);
+}
+
+CONSTCD11
+inline
+bool
+operator>=(const weeknum_weekday& x, const weeknum_weekday& y) NOEXCEPT
+{
+    return !(x < y);
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const weeknum_weekday& md)
+{
+    return os << md.weeknum() << '-' << md.weekday();
+}
+
+// lastweek_weekday
+
+CONSTCD11
+inline
+lastweek_weekday::lastweek_weekday(const iso_week::weekday& wd) NOEXCEPT
+    : wd_(wd)
+    {}
+
+CONSTCD11 inline weekday lastweek_weekday::weekday() const NOEXCEPT {return wd_;}
+
+CONSTCD14
+inline
+bool
+lastweek_weekday::ok() const NOEXCEPT
+{
+    return wd_.ok();
+}
+
+CONSTCD11
+inline
+bool
+operator==(const lastweek_weekday& x, const lastweek_weekday& y) NOEXCEPT
+{
+    return x.weekday() == y.weekday();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const lastweek_weekday& x, const lastweek_weekday& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+CONSTCD11
+inline
+bool
+operator<(const lastweek_weekday& x, const lastweek_weekday& y) NOEXCEPT
+{
+    return static_cast<unsigned>(x.weekday()) < static_cast<unsigned>(y.weekday());
+}
+
+CONSTCD11
+inline
+bool
+operator>(const lastweek_weekday& x, const lastweek_weekday& y) NOEXCEPT
+{
+    return y < x;
+}
+
+CONSTCD11
+inline
+bool
+operator<=(const lastweek_weekday& x, const lastweek_weekday& y) NOEXCEPT
+{
+    return !(y < x);
+}
+
+CONSTCD11
+inline
+bool
+operator>=(const lastweek_weekday& x, const lastweek_weekday& y) NOEXCEPT
+{
+    return !(x < y);
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const lastweek_weekday& md)
+{
+    return os << "W last-" << md.weekday();
+}
+
+// year_lastweek_weekday
+
+CONSTCD11
+inline
+year_lastweek_weekday::year_lastweek_weekday(const iso_week::year& y,
+                                             const iso_week::weekday& wd) NOEXCEPT
+    : y_(y)
+    , wd_(wd)
+    {}
+
+inline
+year_lastweek_weekday&
+year_lastweek_weekday::operator+=(const years& y) NOEXCEPT
+{
+    *this = *this + y;
+    return *this;
+}
+
+inline
+year_lastweek_weekday&
+year_lastweek_weekday::operator-=(const years& y) NOEXCEPT
+{
+    *this = *this - y;
+    return *this;
+}
+
+CONSTCD11 inline year year_lastweek_weekday::year() const NOEXCEPT {return y_;}
+
+CONSTCD14
+inline
+weeknum
+year_lastweek_weekday::weeknum() const NOEXCEPT
+{
+    return (y_ / last).weeknum();
+}
+
+CONSTCD11 inline weekday year_lastweek_weekday::weekday() const NOEXCEPT {return wd_;}
+
+CONSTCD14
+inline
+year_lastweek_weekday::operator sys_days() const NOEXCEPT
+{
+    return sys_days(date::year{static_cast<int>(y_)}/date::dec/date::thu[date::last])
+         + (sun - thu) - (sun - wd_);
+}
+
+CONSTCD14
+inline
+year_lastweek_weekday::operator local_days() const NOEXCEPT
+{
+    return local_days(date::year{static_cast<int>(y_)}/date::dec/date::thu[date::last])
+         + (sun - thu) - (sun - wd_);
+}
+
+CONSTCD11
+inline
+bool
+year_lastweek_weekday::ok() const NOEXCEPT
+{
+    return y_.ok() && wd_.ok();
+}
+
+CONSTCD11
+inline
+bool
+operator==(const year_lastweek_weekday& x, const year_lastweek_weekday& y) NOEXCEPT
+{
+    return x.year() == y.year() && x.weekday() == y.weekday();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const year_lastweek_weekday& x, const year_lastweek_weekday& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+CONSTCD11
+inline
+bool
+operator<(const year_lastweek_weekday& x, const year_lastweek_weekday& y) NOEXCEPT
+{
+    return x.year() < y.year() ? true
+        : (x.year() > y.year() ? false
+        : (static_cast<unsigned>(x.weekday()) < static_cast<unsigned>(y.weekday())));
+}
+
+CONSTCD11
+inline
+bool
+operator>(const year_lastweek_weekday& x, const year_lastweek_weekday& y) NOEXCEPT
+{
+    return y < x;
+}
+
+CONSTCD11
+inline
+bool
+operator<=(const year_lastweek_weekday& x, const year_lastweek_weekday& y) NOEXCEPT
+{
+    return !(y < x);
+}
+
+CONSTCD11
+inline
+bool
+operator>=(const year_lastweek_weekday& x, const year_lastweek_weekday& y) NOEXCEPT
+{
+    return !(x < y);
+}
+
+CONSTCD11
+inline
+year_lastweek_weekday
+operator+(const year_lastweek_weekday& ywnwd, const years& y)  NOEXCEPT
+{
+    return (ywnwd.year() + y) / last / ywnwd.weekday();
+}
+
+CONSTCD11
+inline
+year_lastweek_weekday
+operator+(const years& y, const year_lastweek_weekday& ywnwd)  NOEXCEPT
+{
+    return ywnwd + y;
+}
+
+CONSTCD11
+inline
+year_lastweek_weekday
+operator-(const year_lastweek_weekday& ywnwd, const years& y)  NOEXCEPT
+{
+    return ywnwd + -y;
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_lastweek_weekday& ywnwd)
+{
+    return os << ywnwd.year() << "-W last-" << ywnwd.weekday();
+}
+
+// year_weeknum_weekday
+
+CONSTCD11
+inline
+year_weeknum_weekday::year_weeknum_weekday(const iso_week::year& y,
+                                           const iso_week::weeknum& wn,
+                                           const iso_week::weekday& wd) NOEXCEPT
+    : y_(y)
+    , wn_(wn)
+    , wd_(wd)
+    {}
+
+CONSTCD14
+inline
+year_weeknum_weekday::year_weeknum_weekday(const year_lastweek_weekday& ylwwd) NOEXCEPT
+    : y_(ylwwd.year())
+    , wn_(ylwwd.weeknum())
+    , wd_(ylwwd.weekday())
+    {}
+
+CONSTCD14
+inline
+year_weeknum_weekday::year_weeknum_weekday(const sys_days& dp) NOEXCEPT
+    : year_weeknum_weekday(from_days(dp.time_since_epoch()))
+    {}
+
+CONSTCD14
+inline
+year_weeknum_weekday::year_weeknum_weekday(const local_days& dp) NOEXCEPT
+    : year_weeknum_weekday(from_days(dp.time_since_epoch()))
+    {}
+
+inline
+year_weeknum_weekday&
+year_weeknum_weekday::operator+=(const years& y) NOEXCEPT
+{
+    *this = *this + y;
+    return *this;
+}
+
+inline
+year_weeknum_weekday&
+year_weeknum_weekday::operator-=(const years& y) NOEXCEPT
+{
+    *this = *this - y;
+    return *this;
+}
+
+CONSTCD11 inline year year_weeknum_weekday::year() const NOEXCEPT {return y_;}
+CONSTCD11 inline weeknum year_weeknum_weekday::weeknum() const NOEXCEPT {return wn_;}
+CONSTCD11 inline weekday year_weeknum_weekday::weekday() const NOEXCEPT {return wd_;}
+
+CONSTCD14
+inline
+year_weeknum_weekday::operator sys_days() const NOEXCEPT
+{
+    return sys_days(date::year{static_cast<int>(y_)-1}/date::dec/date::thu[date::last])
+         + (date::mon - date::thu) + weeks{static_cast<unsigned>(wn_)-1} + (wd_ - mon);
+}
+
+CONSTCD14
+inline
+year_weeknum_weekday::operator local_days() const NOEXCEPT
+{
+    return local_days(date::year{static_cast<int>(y_)-1}/date::dec/date::thu[date::last])
+         + (date::mon - date::thu) + weeks{static_cast<unsigned>(wn_)-1} + (wd_ - mon);
+}
+
+CONSTCD14
+inline
+bool
+year_weeknum_weekday::ok() const NOEXCEPT
+{
+    return y_.ok() && wd_.ok() && iso_week::weeknum{1u} <= wn_ && wn_ <= year_lastweek{y_}.weeknum();
+}
+
+CONSTCD14
+inline
+year_weeknum_weekday
+year_weeknum_weekday::from_days(days d) NOEXCEPT
+{
+    const auto dp = sys_days{d};
+    const auto wd = iso_week::weekday{dp};
+    auto y = date::year_month_day{dp + days{3}}.year();
+    auto start = sys_days((y - date::years{1})/date::dec/date::thu[date::last]) + (mon-thu);
+    if (dp < start)
+    {
+        --y;
+        start = sys_days((y - date::years{1})/date::dec/date::thu[date::last]) + (mon-thu);
+    }
+    const auto wn = iso_week::weeknum(
+                       static_cast<unsigned>(date::trunc<weeks>(dp - start).count() + 1));
+    return {iso_week::year(static_cast<int>(y)), wn, wd};
+}
+
+CONSTCD11
+inline
+bool
+operator==(const year_weeknum_weekday& x, const year_weeknum_weekday& y) NOEXCEPT
+{
+    return x.year() == y.year() && x.weeknum() == y.weeknum() && x.weekday() == y.weekday();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const year_weeknum_weekday& x, const year_weeknum_weekday& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+CONSTCD11
+inline
+bool
+operator<(const year_weeknum_weekday& x, const year_weeknum_weekday& y) NOEXCEPT
+{
+    return x.year() < y.year() ? true
+        : (x.year() > y.year() ? false
+        : (x.weeknum() < y.weeknum() ? true
+        : (x.weeknum() > y.weeknum() ? false
+        : (static_cast<unsigned>(x.weekday()) < static_cast<unsigned>(y.weekday())))));
+}
+
+CONSTCD11
+inline
+bool
+operator>(const year_weeknum_weekday& x, const year_weeknum_weekday& y) NOEXCEPT
+{
+    return y < x;
+}
+
+CONSTCD11
+inline
+bool
+operator<=(const year_weeknum_weekday& x, const year_weeknum_weekday& y) NOEXCEPT
+{
+    return !(y < x);
+}
+
+CONSTCD11
+inline
+bool
+operator>=(const year_weeknum_weekday& x, const year_weeknum_weekday& y) NOEXCEPT
+{
+    return !(x < y);
+}
+
+CONSTCD11
+inline
+year_weeknum_weekday
+operator+(const year_weeknum_weekday& ywnwd, const years& y)  NOEXCEPT
+{
+    return (ywnwd.year() + y) / ywnwd.weeknum() / ywnwd.weekday();
+}
+
+CONSTCD11
+inline
+year_weeknum_weekday
+operator+(const years& y, const year_weeknum_weekday& ywnwd)  NOEXCEPT
+{
+    return ywnwd + y;
+}
+
+CONSTCD11
+inline
+year_weeknum_weekday
+operator-(const year_weeknum_weekday& ywnwd, const years& y)  NOEXCEPT
+{
+    return ywnwd + -y;
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_weeknum_weekday& ywnwd)
+{
+    return os << ywnwd.year() << '-' << ywnwd.weeknum() << '-' << ywnwd.weekday();
+}
+
+// date composition operators
+
+CONSTCD11
+inline
+year_weeknum
+operator/(const year& y, const weeknum& wn) NOEXCEPT
+{
+    return {y, wn};
+}
+
+CONSTCD11
+inline
+year_weeknum
+operator/(const year& y, int wn) NOEXCEPT
+{
+    return y/weeknum(static_cast<unsigned>(wn));
+}
+
+CONSTCD11
+inline
+year_lastweek
+operator/(const year& y, last_week) NOEXCEPT
+{
+    return year_lastweek{y};
+}
+
+CONSTCD11
+inline
+weeknum_weekday
+operator/(const weeknum& wn, const weekday& wd) NOEXCEPT
+{
+    return {wn, wd};
+}
+
+CONSTCD11
+inline
+weeknum_weekday
+operator/(const weeknum& wn, int wd) NOEXCEPT
+{
+    return wn/weekday{static_cast<unsigned>(wd)};
+}
+
+CONSTCD11
+inline
+weeknum_weekday
+operator/(const weekday& wd, const weeknum& wn) NOEXCEPT
+{
+    return wn/wd;
+}
+
+CONSTCD11
+inline
+weeknum_weekday
+operator/(const weekday& wd, int wn) NOEXCEPT
+{
+    return weeknum{static_cast<unsigned>(wn)}/wd;
+}
+
+CONSTCD11
+inline
+lastweek_weekday
+operator/(const last_week&, const weekday& wd) NOEXCEPT
+{
+    return lastweek_weekday{wd};
+}
+
+CONSTCD11
+inline
+lastweek_weekday
+operator/(const last_week& wn, int wd) NOEXCEPT
+{
+    return wn / weekday{static_cast<unsigned>(wd)};
+}
+
+CONSTCD11
+inline
+lastweek_weekday
+operator/(const weekday& wd, const last_week& wn) NOEXCEPT
+{
+    return wn / wd;
+}
+
+CONSTCD11
+inline
+year_weeknum_weekday
+operator/(const year_weeknum& ywn, const weekday& wd) NOEXCEPT
+{
+    return {ywn.year(), ywn.weeknum(), wd};
+}
+
+CONSTCD11
+inline
+year_weeknum_weekday
+operator/(const year_weeknum& ywn, int wd) NOEXCEPT
+{
+    return ywn / weekday(static_cast<unsigned>(wd));
+}
+
+CONSTCD11
+inline
+year_weeknum_weekday
+operator/(const weeknum_weekday& wnwd, const year& y) NOEXCEPT
+{
+    return {y, wnwd.weeknum(), wnwd.weekday()};
+}
+
+CONSTCD11
+inline
+year_weeknum_weekday
+operator/(const weeknum_weekday& wnwd, int y) NOEXCEPT
+{
+    return wnwd / year{y};
+}
+
+CONSTCD11
+inline
+year_lastweek_weekday
+operator/(const year_lastweek& ylw, const weekday& wd) NOEXCEPT
+{
+    return {ylw.year(), wd};
+}
+
+CONSTCD11
+inline
+year_lastweek_weekday
+operator/(const year_lastweek& ylw, int wd) NOEXCEPT
+{
+    return ylw / weekday(static_cast<unsigned>(wd));
+}
+
+CONSTCD11
+inline
+year_lastweek_weekday
+operator/(const lastweek_weekday& lwwd, const year& y) NOEXCEPT
+{
+    return {y, lwwd.weekday()};
+}
+
+CONSTCD11
+inline
+year_lastweek_weekday
+operator/(const lastweek_weekday& lwwd, int y) NOEXCEPT
+{
+    return lwwd / year{y};
+}
+
+}  // namespace iso_week
+
+#endif  // ISO_WEEK_H
diff --git a/third_party/date-3.0.1/include/date/julian.h b/third_party/date-3.0.1/include/date/julian.h
new file mode 100644
index 00000000..d909d69b
--- /dev/null
+++ b/third_party/date-3.0.1/include/date/julian.h
@@ -0,0 +1,3052 @@
+#ifndef JULIAN_H
+#define JULIAN_H
+
+// The MIT License (MIT)
+//
+// Copyright (c) 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+//
+// Our apologies.  When the previous paragraph was written, lowercase had not yet
+// been invented (that would involve another several millennia of evolution).
+// We did not mean to shout.
+
+#include "date.h"
+
+namespace julian
+{
+
+// durations
+
+using days = date::days;
+
+using weeks = date::weeks;
+
+using years = std::chrono::duration
+    <int, date::detail::ratio_multiply<std::ratio<1461, 4>, days::period>>;
+
+using months = std::chrono::duration
+    <int, date::detail::ratio_divide<years::period, std::ratio<12>>>;
+
+// time_point
+
+using sys_days   = date::sys_days;
+using local_days = date::local_days;
+
+// types
+
+struct last_spec
+{
+    explicit last_spec() = default;
+};
+
+class day;
+class month;
+class year;
+
+class weekday;
+class weekday_indexed;
+class weekday_last;
+
+class month_day;
+class month_day_last;
+class month_weekday;
+class month_weekday_last;
+
+class year_month;
+
+class year_month_day;
+class year_month_day_last;
+class year_month_weekday;
+class year_month_weekday_last;
+
+// date composition operators
+
+CONSTCD11 year_month operator/(const year& y, const month& m) NOEXCEPT;
+CONSTCD11 year_month operator/(const year& y, int          m) NOEXCEPT;
+
+CONSTCD11 month_day operator/(const day& d, const month& m) NOEXCEPT;
+CONSTCD11 month_day operator/(const day& d, int          m) NOEXCEPT;
+CONSTCD11 month_day operator/(const month& m, const day& d) NOEXCEPT;
+CONSTCD11 month_day operator/(const month& m, int        d) NOEXCEPT;
+CONSTCD11 month_day operator/(int          m, const day& d) NOEXCEPT;
+
+CONSTCD11 month_day_last operator/(const month& m, last_spec) NOEXCEPT;
+CONSTCD11 month_day_last operator/(int          m, last_spec) NOEXCEPT;
+CONSTCD11 month_day_last operator/(last_spec, const month& m) NOEXCEPT;
+CONSTCD11 month_day_last operator/(last_spec, int          m) NOEXCEPT;
+
+CONSTCD11 month_weekday operator/(const month& m, const weekday_indexed& wdi) NOEXCEPT;
+CONSTCD11 month_weekday operator/(int          m, const weekday_indexed& wdi) NOEXCEPT;
+CONSTCD11 month_weekday operator/(const weekday_indexed& wdi, const month& m) NOEXCEPT;
+CONSTCD11 month_weekday operator/(const weekday_indexed& wdi, int          m) NOEXCEPT;
+
+CONSTCD11 month_weekday_last operator/(const month& m, const weekday_last& wdl) NOEXCEPT;
+CONSTCD11 month_weekday_last operator/(int          m, const weekday_last& wdl) NOEXCEPT;
+CONSTCD11 month_weekday_last operator/(const weekday_last& wdl, const month& m) NOEXCEPT;
+CONSTCD11 month_weekday_last operator/(const weekday_last& wdl, int          m) NOEXCEPT;
+
+CONSTCD11 year_month_day operator/(const year_month& ym, const day& d) NOEXCEPT;
+CONSTCD11 year_month_day operator/(const year_month& ym, int        d) NOEXCEPT;
+CONSTCD11 year_month_day operator/(const year& y, const month_day& md) NOEXCEPT;
+CONSTCD11 year_month_day operator/(int         y, const month_day& md) NOEXCEPT;
+CONSTCD11 year_month_day operator/(const month_day& md, const year& y) NOEXCEPT;
+CONSTCD11 year_month_day operator/(const month_day& md, int         y) NOEXCEPT;
+
+CONSTCD11
+    year_month_day_last operator/(const year_month& ym,   last_spec) NOEXCEPT;
+CONSTCD11
+    year_month_day_last operator/(const year& y, const month_day_last& mdl) NOEXCEPT;
+CONSTCD11
+    year_month_day_last operator/(int         y, const month_day_last& mdl) NOEXCEPT;
+CONSTCD11
+    year_month_day_last operator/(const month_day_last& mdl, const year& y) NOEXCEPT;
+CONSTCD11
+    year_month_day_last operator/(const month_day_last& mdl, int         y) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday
+operator/(const year_month& ym, const weekday_indexed& wdi) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday
+operator/(const year&        y, const month_weekday&   mwd) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday
+operator/(int                y, const month_weekday&   mwd) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday
+operator/(const month_weekday& mwd, const year&          y) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday
+operator/(const month_weekday& mwd, int                  y) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday_last
+operator/(const year_month& ym, const weekday_last& wdl) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday_last
+operator/(const year& y, const month_weekday_last& mwdl) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday_last
+operator/(int         y, const month_weekday_last& mwdl) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday_last
+operator/(const month_weekday_last& mwdl, const year& y) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday_last
+operator/(const month_weekday_last& mwdl, int         y) NOEXCEPT;
+
+// Detailed interface
+
+// day
+
+class day
+{
+    unsigned char d_;
+
+public:
+    explicit CONSTCD11 day(unsigned d) NOEXCEPT;
+
+    CONSTCD14 day& operator++()    NOEXCEPT;
+    CONSTCD14 day  operator++(int) NOEXCEPT;
+    CONSTCD14 day& operator--()    NOEXCEPT;
+    CONSTCD14 day  operator--(int) NOEXCEPT;
+
+    CONSTCD14 day& operator+=(const days& d) NOEXCEPT;
+    CONSTCD14 day& operator-=(const days& d) NOEXCEPT;
+
+    CONSTCD11 explicit operator unsigned() const NOEXCEPT;
+    CONSTCD11 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const day& x, const day& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const day& x, const day& y) NOEXCEPT;
+CONSTCD11 bool operator< (const day& x, const day& y) NOEXCEPT;
+CONSTCD11 bool operator> (const day& x, const day& y) NOEXCEPT;
+CONSTCD11 bool operator<=(const day& x, const day& y) NOEXCEPT;
+CONSTCD11 bool operator>=(const day& x, const day& y) NOEXCEPT;
+
+CONSTCD11 day  operator+(const day&  x, const days& y) NOEXCEPT;
+CONSTCD11 day  operator+(const days& x, const day&  y) NOEXCEPT;
+CONSTCD11 day  operator-(const day&  x, const days& y) NOEXCEPT;
+CONSTCD11 days operator-(const day&  x, const day&  y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const day& d);
+
+// month
+
+class month
+{
+    unsigned char m_;
+
+public:
+    explicit CONSTCD11 month(unsigned m) NOEXCEPT;
+
+    CONSTCD14 month& operator++()    NOEXCEPT;
+    CONSTCD14 month  operator++(int) NOEXCEPT;
+    CONSTCD14 month& operator--()    NOEXCEPT;
+    CONSTCD14 month  operator--(int) NOEXCEPT;
+
+    CONSTCD14 month& operator+=(const months& m) NOEXCEPT;
+    CONSTCD14 month& operator-=(const months& m) NOEXCEPT;
+
+    CONSTCD11 explicit operator unsigned() const NOEXCEPT;
+    CONSTCD11 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const month& x, const month& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const month& x, const month& y) NOEXCEPT;
+CONSTCD11 bool operator< (const month& x, const month& y) NOEXCEPT;
+CONSTCD11 bool operator> (const month& x, const month& y) NOEXCEPT;
+CONSTCD11 bool operator<=(const month& x, const month& y) NOEXCEPT;
+CONSTCD11 bool operator>=(const month& x, const month& y) NOEXCEPT;
+
+CONSTCD14 month  operator+(const month&  x, const months& y) NOEXCEPT;
+CONSTCD14 month  operator+(const months& x,  const month& y) NOEXCEPT;
+CONSTCD14 month  operator-(const month&  x, const months& y) NOEXCEPT;
+CONSTCD14 months operator-(const month&  x,  const month& y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const month& m);
+
+// year
+
+class year
+{
+    short y_;
+
+public:
+    explicit CONSTCD11 year(int y) NOEXCEPT;
+
+    CONSTCD14 year& operator++()    NOEXCEPT;
+    CONSTCD14 year  operator++(int) NOEXCEPT;
+    CONSTCD14 year& operator--()    NOEXCEPT;
+    CONSTCD14 year  operator--(int) NOEXCEPT;
+
+    CONSTCD14 year& operator+=(const years& y) NOEXCEPT;
+    CONSTCD14 year& operator-=(const years& y) NOEXCEPT;
+
+    CONSTCD11 bool is_leap() const NOEXCEPT;
+
+    CONSTCD11 explicit operator int() const NOEXCEPT;
+    CONSTCD11 bool ok() const NOEXCEPT;
+
+    static CONSTCD11 year min() NOEXCEPT;
+    static CONSTCD11 year max() NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const year& x, const year& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const year& x, const year& y) NOEXCEPT;
+CONSTCD11 bool operator< (const year& x, const year& y) NOEXCEPT;
+CONSTCD11 bool operator> (const year& x, const year& y) NOEXCEPT;
+CONSTCD11 bool operator<=(const year& x, const year& y) NOEXCEPT;
+CONSTCD11 bool operator>=(const year& x, const year& y) NOEXCEPT;
+
+CONSTCD11 year  operator+(const year&  x, const years& y) NOEXCEPT;
+CONSTCD11 year  operator+(const years& x, const year&  y) NOEXCEPT;
+CONSTCD11 year  operator-(const year&  x, const years& y) NOEXCEPT;
+CONSTCD11 years operator-(const year&  x, const year&  y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year& y);
+
+// weekday
+
+class weekday
+{
+    unsigned char wd_;
+public:
+    explicit CONSTCD11 weekday(unsigned wd) NOEXCEPT;
+    explicit weekday(int) = delete;
+    CONSTCD11 weekday(const sys_days& dp) NOEXCEPT;
+    CONSTCD11 explicit weekday(const local_days& dp) NOEXCEPT;
+
+    CONSTCD14 weekday& operator++()    NOEXCEPT;
+    CONSTCD14 weekday  operator++(int) NOEXCEPT;
+    CONSTCD14 weekday& operator--()    NOEXCEPT;
+    CONSTCD14 weekday  operator--(int) NOEXCEPT;
+
+    CONSTCD14 weekday& operator+=(const days& d) NOEXCEPT;
+    CONSTCD14 weekday& operator-=(const days& d) NOEXCEPT;
+
+    CONSTCD11 explicit operator unsigned() const NOEXCEPT;
+    CONSTCD11 bool ok() const NOEXCEPT;
+
+    CONSTCD11 weekday_indexed operator[](unsigned index) const NOEXCEPT;
+    CONSTCD11 weekday_last    operator[](last_spec)      const NOEXCEPT;
+
+private:
+    static CONSTCD11 unsigned char weekday_from_days(int z) NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const weekday& x, const weekday& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const weekday& x, const weekday& y) NOEXCEPT;
+
+CONSTCD14 weekday operator+(const weekday& x, const days&    y) NOEXCEPT;
+CONSTCD14 weekday operator+(const days&    x, const weekday& y) NOEXCEPT;
+CONSTCD14 weekday operator-(const weekday& x, const days&    y) NOEXCEPT;
+CONSTCD14 days    operator-(const weekday& x, const weekday& y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const weekday& wd);
+
+// weekday_indexed
+
+class weekday_indexed
+{
+    unsigned char wd_    : 4;
+    unsigned char index_ : 4;
+
+public:
+    CONSTCD11 weekday_indexed(const julian::weekday& wd, unsigned index) NOEXCEPT;
+
+    CONSTCD11 julian::weekday weekday() const NOEXCEPT;
+    CONSTCD11 unsigned index() const NOEXCEPT;
+    CONSTCD11 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const weekday_indexed& x, const weekday_indexed& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const weekday_indexed& x, const weekday_indexed& y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const weekday_indexed& wdi);
+
+// weekday_last
+
+class weekday_last
+{
+    julian::weekday wd_;
+
+public:
+    explicit CONSTCD11 weekday_last(const julian::weekday& wd) NOEXCEPT;
+
+    CONSTCD11 julian::weekday weekday() const NOEXCEPT;
+    CONSTCD11 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const weekday_last& x, const weekday_last& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const weekday_last& x, const weekday_last& y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const weekday_last& wdl);
+
+// year_month
+
+class year_month
+{
+    julian::year  y_;
+    julian::month m_;
+
+public:
+    CONSTCD11 year_month(const julian::year& y, const julian::month& m) NOEXCEPT;
+
+    CONSTCD11 julian::year  year()  const NOEXCEPT;
+    CONSTCD11 julian::month month() const NOEXCEPT;
+
+    CONSTCD14 year_month& operator+=(const months& dm) NOEXCEPT;
+    CONSTCD14 year_month& operator-=(const months& dm) NOEXCEPT;
+    CONSTCD14 year_month& operator+=(const years& dy) NOEXCEPT;
+    CONSTCD14 year_month& operator-=(const years& dy) NOEXCEPT;
+
+    CONSTCD11 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const year_month& x, const year_month& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const year_month& x, const year_month& y) NOEXCEPT;
+CONSTCD11 bool operator< (const year_month& x, const year_month& y) NOEXCEPT;
+CONSTCD11 bool operator> (const year_month& x, const year_month& y) NOEXCEPT;
+CONSTCD11 bool operator<=(const year_month& x, const year_month& y) NOEXCEPT;
+CONSTCD11 bool operator>=(const year_month& x, const year_month& y) NOEXCEPT;
+
+CONSTCD14 year_month operator+(const year_month& ym, const months& dm) NOEXCEPT;
+CONSTCD14 year_month operator+(const months& dm, const year_month& ym) NOEXCEPT;
+CONSTCD14 year_month operator-(const year_month& ym, const months& dm) NOEXCEPT;
+
+CONSTCD11 months operator-(const year_month& x, const year_month& y) NOEXCEPT;
+CONSTCD11 year_month operator+(const year_month& ym, const years& dy) NOEXCEPT;
+CONSTCD11 year_month operator+(const years& dy, const year_month& ym) NOEXCEPT;
+CONSTCD11 year_month operator-(const year_month& ym, const years& dy) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_month& ym);
+
+// month_day
+
+class month_day
+{
+    julian::month m_;
+    julian::day   d_;
+
+public:
+    CONSTCD11 month_day(const julian::month& m, const julian::day& d) NOEXCEPT;
+
+    CONSTCD11 julian::month month() const NOEXCEPT;
+    CONSTCD11 julian::day   day() const NOEXCEPT;
+
+    CONSTCD14 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const month_day& x, const month_day& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const month_day& x, const month_day& y) NOEXCEPT;
+CONSTCD11 bool operator< (const month_day& x, const month_day& y) NOEXCEPT;
+CONSTCD11 bool operator> (const month_day& x, const month_day& y) NOEXCEPT;
+CONSTCD11 bool operator<=(const month_day& x, const month_day& y) NOEXCEPT;
+CONSTCD11 bool operator>=(const month_day& x, const month_day& y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const month_day& md);
+
+// month_day_last
+
+class month_day_last
+{
+    julian::month m_;
+
+public:
+    CONSTCD11 explicit month_day_last(const julian::month& m) NOEXCEPT;
+
+    CONSTCD11 julian::month month() const NOEXCEPT;
+    CONSTCD11 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const month_day_last& x, const month_day_last& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const month_day_last& x, const month_day_last& y) NOEXCEPT;
+CONSTCD11 bool operator< (const month_day_last& x, const month_day_last& y) NOEXCEPT;
+CONSTCD11 bool operator> (const month_day_last& x, const month_day_last& y) NOEXCEPT;
+CONSTCD11 bool operator<=(const month_day_last& x, const month_day_last& y) NOEXCEPT;
+CONSTCD11 bool operator>=(const month_day_last& x, const month_day_last& y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const month_day_last& mdl);
+
+// month_weekday
+
+class month_weekday
+{
+    julian::month           m_;
+    julian::weekday_indexed wdi_;
+public:
+    CONSTCD11 month_weekday(const julian::month& m,
+                            const julian::weekday_indexed& wdi) NOEXCEPT;
+
+    CONSTCD11 julian::month           month()           const NOEXCEPT;
+    CONSTCD11 julian::weekday_indexed weekday_indexed() const NOEXCEPT;
+
+    CONSTCD11 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const month_weekday& x, const month_weekday& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const month_weekday& x, const month_weekday& y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const month_weekday& mwd);
+
+// month_weekday_last
+
+class month_weekday_last
+{
+    julian::month        m_;
+    julian::weekday_last wdl_;
+
+public:
+    CONSTCD11 month_weekday_last(const julian::month& m,
+                                 const julian::weekday_last& wd) NOEXCEPT;
+
+    CONSTCD11 julian::month        month()        const NOEXCEPT;
+    CONSTCD11 julian::weekday_last weekday_last() const NOEXCEPT;
+
+    CONSTCD11 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11
+    bool operator==(const month_weekday_last& x, const month_weekday_last& y) NOEXCEPT;
+CONSTCD11
+    bool operator!=(const month_weekday_last& x, const month_weekday_last& y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const month_weekday_last& mwdl);
+
+// class year_month_day
+
+class year_month_day
+{
+    julian::year  y_;
+    julian::month m_;
+    julian::day   d_;
+
+public:
+    CONSTCD11 year_month_day(const julian::year& y, const julian::month& m,
+                             const julian::day& d) NOEXCEPT;
+    CONSTCD14 year_month_day(const year_month_day_last& ymdl) NOEXCEPT;
+
+    CONSTCD14 year_month_day(sys_days dp) NOEXCEPT;
+    CONSTCD14 explicit year_month_day(local_days dp) NOEXCEPT;
+
+    CONSTCD14 year_month_day& operator+=(const months& m) NOEXCEPT;
+    CONSTCD14 year_month_day& operator-=(const months& m) NOEXCEPT;
+    CONSTCD14 year_month_day& operator+=(const years& y)  NOEXCEPT;
+    CONSTCD14 year_month_day& operator-=(const years& y)  NOEXCEPT;
+
+    CONSTCD11 julian::year  year()  const NOEXCEPT;
+    CONSTCD11 julian::month month() const NOEXCEPT;
+    CONSTCD11 julian::day   day()   const NOEXCEPT;
+
+    CONSTCD14 operator sys_days() const NOEXCEPT;
+    CONSTCD14 explicit operator local_days() const NOEXCEPT;
+    CONSTCD14 bool ok() const NOEXCEPT;
+
+private:
+    static CONSTCD14 year_month_day from_days(days dp) NOEXCEPT;
+    CONSTCD14 days to_days() const NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const year_month_day& x, const year_month_day& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const year_month_day& x, const year_month_day& y) NOEXCEPT;
+CONSTCD11 bool operator< (const year_month_day& x, const year_month_day& y) NOEXCEPT;
+CONSTCD11 bool operator> (const year_month_day& x, const year_month_day& y) NOEXCEPT;
+CONSTCD11 bool operator<=(const year_month_day& x, const year_month_day& y) NOEXCEPT;
+CONSTCD11 bool operator>=(const year_month_day& x, const year_month_day& y) NOEXCEPT;
+
+CONSTCD14 year_month_day operator+(const year_month_day& ymd, const months& dm) NOEXCEPT;
+CONSTCD14 year_month_day operator+(const months& dm, const year_month_day& ymd) NOEXCEPT;
+CONSTCD14 year_month_day operator-(const year_month_day& ymd, const months& dm) NOEXCEPT;
+CONSTCD11 year_month_day operator+(const year_month_day& ymd, const years& dy)  NOEXCEPT;
+CONSTCD11 year_month_day operator+(const years& dy, const year_month_day& ymd)  NOEXCEPT;
+CONSTCD11 year_month_day operator-(const year_month_day& ymd, const years& dy)  NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_month_day& ymd);
+
+// year_month_day_last
+
+class year_month_day_last
+{
+    julian::year           y_;
+    julian::month_day_last mdl_;
+
+public:
+    CONSTCD11 year_month_day_last(const julian::year& y,
+                                  const julian::month_day_last& mdl) NOEXCEPT;
+
+    CONSTCD14 year_month_day_last& operator+=(const months& m) NOEXCEPT;
+    CONSTCD14 year_month_day_last& operator-=(const months& m) NOEXCEPT;
+    CONSTCD14 year_month_day_last& operator+=(const years& y)  NOEXCEPT;
+    CONSTCD14 year_month_day_last& operator-=(const years& y)  NOEXCEPT;
+
+    CONSTCD11 julian::year           year()           const NOEXCEPT;
+    CONSTCD11 julian::month          month()          const NOEXCEPT;
+    CONSTCD11 julian::month_day_last month_day_last() const NOEXCEPT;
+    CONSTCD14 julian::day            day()            const NOEXCEPT;
+
+    CONSTCD14 operator sys_days() const NOEXCEPT;
+    CONSTCD14 explicit operator local_days() const NOEXCEPT;
+    CONSTCD11 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11
+    bool operator==(const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT;
+CONSTCD11
+    bool operator!=(const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT;
+CONSTCD11
+    bool operator< (const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT;
+CONSTCD11
+    bool operator> (const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT;
+CONSTCD11
+    bool operator<=(const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT;
+CONSTCD11
+    bool operator>=(const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT;
+
+CONSTCD14
+year_month_day_last
+operator+(const year_month_day_last& ymdl, const months& dm) NOEXCEPT;
+
+CONSTCD14
+year_month_day_last
+operator+(const months& dm, const year_month_day_last& ymdl) NOEXCEPT;
+
+CONSTCD11
+year_month_day_last
+operator+(const year_month_day_last& ymdl, const years& dy) NOEXCEPT;
+
+CONSTCD11
+year_month_day_last
+operator+(const years& dy, const year_month_day_last& ymdl) NOEXCEPT;
+
+CONSTCD14
+year_month_day_last
+operator-(const year_month_day_last& ymdl, const months& dm) NOEXCEPT;
+
+CONSTCD11
+year_month_day_last
+operator-(const year_month_day_last& ymdl, const years& dy) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_month_day_last& ymdl);
+
+// year_month_weekday
+
+class year_month_weekday
+{
+    julian::year            y_;
+    julian::month           m_;
+    julian::weekday_indexed wdi_;
+
+public:
+    CONSTCD11 year_month_weekday(const julian::year& y, const julian::month& m,
+                                   const julian::weekday_indexed& wdi) NOEXCEPT;
+    CONSTCD14 year_month_weekday(const sys_days& dp) NOEXCEPT;
+    CONSTCD14 explicit year_month_weekday(const local_days& dp) NOEXCEPT;
+
+    CONSTCD14 year_month_weekday& operator+=(const months& m) NOEXCEPT;
+    CONSTCD14 year_month_weekday& operator-=(const months& m) NOEXCEPT;
+    CONSTCD14 year_month_weekday& operator+=(const years& y)  NOEXCEPT;
+    CONSTCD14 year_month_weekday& operator-=(const years& y)  NOEXCEPT;
+
+    CONSTCD11 julian::year year() const NOEXCEPT;
+    CONSTCD11 julian::month month() const NOEXCEPT;
+    CONSTCD11 julian::weekday weekday() const NOEXCEPT;
+    CONSTCD11 unsigned index() const NOEXCEPT;
+    CONSTCD11 julian::weekday_indexed weekday_indexed() const NOEXCEPT;
+
+    CONSTCD14 operator sys_days() const NOEXCEPT;
+    CONSTCD14 explicit operator local_days() const NOEXCEPT;
+    CONSTCD14 bool ok() const NOEXCEPT;
+
+private:
+    static CONSTCD14 year_month_weekday from_days(days dp) NOEXCEPT;
+    CONSTCD14 days to_days() const NOEXCEPT;
+};
+
+CONSTCD11
+    bool operator==(const year_month_weekday& x, const year_month_weekday& y) NOEXCEPT;
+CONSTCD11
+    bool operator!=(const year_month_weekday& x, const year_month_weekday& y) NOEXCEPT;
+
+CONSTCD14
+year_month_weekday
+operator+(const year_month_weekday& ymwd, const months& dm) NOEXCEPT;
+
+CONSTCD14
+year_month_weekday
+operator+(const months& dm, const year_month_weekday& ymwd) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday
+operator+(const year_month_weekday& ymwd, const years& dy) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday
+operator+(const years& dy, const year_month_weekday& ymwd) NOEXCEPT;
+
+CONSTCD14
+year_month_weekday
+operator-(const year_month_weekday& ymwd, const months& dm) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday
+operator-(const year_month_weekday& ymwd, const years& dy) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_month_weekday& ymwdi);
+
+// year_month_weekday_last
+
+class year_month_weekday_last
+{
+    julian::year y_;
+    julian::month m_;
+    julian::weekday_last wdl_;
+
+public:
+    CONSTCD11 year_month_weekday_last(const julian::year& y, const julian::month& m,
+                                      const julian::weekday_last& wdl) NOEXCEPT;
+
+    CONSTCD14 year_month_weekday_last& operator+=(const months& m) NOEXCEPT;
+    CONSTCD14 year_month_weekday_last& operator-=(const months& m) NOEXCEPT;
+    CONSTCD14 year_month_weekday_last& operator+=(const years& y) NOEXCEPT;
+    CONSTCD14 year_month_weekday_last& operator-=(const years& y) NOEXCEPT;
+
+    CONSTCD11 julian::year year() const NOEXCEPT;
+    CONSTCD11 julian::month month() const NOEXCEPT;
+    CONSTCD11 julian::weekday weekday() const NOEXCEPT;
+    CONSTCD11 julian::weekday_last weekday_last() const NOEXCEPT;
+
+    CONSTCD14 operator sys_days() const NOEXCEPT;
+    CONSTCD14 explicit operator local_days() const NOEXCEPT;
+    CONSTCD11 bool ok() const NOEXCEPT;
+
+private:
+    CONSTCD14 days to_days() const NOEXCEPT;
+};
+
+CONSTCD11
+bool
+operator==(const year_month_weekday_last& x, const year_month_weekday_last& y) NOEXCEPT;
+
+CONSTCD11
+bool
+operator!=(const year_month_weekday_last& x, const year_month_weekday_last& y) NOEXCEPT;
+
+CONSTCD14
+year_month_weekday_last
+operator+(const year_month_weekday_last& ymwdl, const months& dm) NOEXCEPT;
+
+CONSTCD14
+year_month_weekday_last
+operator+(const months& dm, const year_month_weekday_last& ymwdl) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday_last
+operator+(const year_month_weekday_last& ymwdl, const years& dy) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday_last
+operator+(const years& dy, const year_month_weekday_last& ymwdl) NOEXCEPT;
+
+CONSTCD14
+year_month_weekday_last
+operator-(const year_month_weekday_last& ymwdl, const months& dm) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday_last
+operator-(const year_month_weekday_last& ymwdl, const years& dy) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_month_weekday_last& ymwdl);
+
+#if !defined(_MSC_VER) || (_MSC_VER >= 1900)
+inline namespace literals
+{
+
+CONSTCD11 julian::day  operator "" _d(unsigned long long d) NOEXCEPT;
+CONSTCD11 julian::year operator "" _y(unsigned long long y) NOEXCEPT;
+
+// CONSTDATA julian::month jan{1};
+// CONSTDATA julian::month feb{2};
+// CONSTDATA julian::month mar{3};
+// CONSTDATA julian::month apr{4};
+// CONSTDATA julian::month may{5};
+// CONSTDATA julian::month jun{6};
+// CONSTDATA julian::month jul{7};
+// CONSTDATA julian::month aug{8};
+// CONSTDATA julian::month sep{9};
+// CONSTDATA julian::month oct{10};
+// CONSTDATA julian::month nov{11};
+// CONSTDATA julian::month dec{12};
+
+}  // inline namespace literals
+#endif // !defined(_MSC_VER) || (_MSC_VER >= 1900)
+
+//----------------+
+// Implementation |
+//----------------+
+
+// day
+
+CONSTCD11 inline day::day(unsigned d) NOEXCEPT : d_(static_cast<unsigned char>(d)) {}
+CONSTCD14 inline day& day::operator++() NOEXCEPT {++d_; return *this;}
+CONSTCD14 inline day day::operator++(int) NOEXCEPT {auto tmp(*this); ++(*this); return tmp;}
+CONSTCD14 inline day& day::operator--() NOEXCEPT {--d_; return *this;}
+CONSTCD14 inline day day::operator--(int) NOEXCEPT {auto tmp(*this); --(*this); return tmp;}
+CONSTCD14 inline day& day::operator+=(const days& d) NOEXCEPT {*this = *this + d; return *this;}
+CONSTCD14 inline day& day::operator-=(const days& d) NOEXCEPT {*this = *this - d; return *this;}
+CONSTCD11 inline day::operator unsigned() const NOEXCEPT {return d_;}
+CONSTCD11 inline bool day::ok() const NOEXCEPT {return 1 <= d_ && d_ <= 31;}
+
+CONSTCD11
+inline
+bool
+operator==(const day& x, const day& y) NOEXCEPT
+{
+    return static_cast<unsigned>(x) == static_cast<unsigned>(y);
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const day& x, const day& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+CONSTCD11
+inline
+bool
+operator<(const day& x, const day& y) NOEXCEPT
+{
+    return static_cast<unsigned>(x) < static_cast<unsigned>(y);
+}
+
+CONSTCD11
+inline
+bool
+operator>(const day& x, const day& y) NOEXCEPT
+{
+    return y < x;
+}
+
+CONSTCD11
+inline
+bool
+operator<=(const day& x, const day& y) NOEXCEPT
+{
+    return !(y < x);
+}
+
+CONSTCD11
+inline
+bool
+operator>=(const day& x, const day& y) NOEXCEPT
+{
+    return !(x < y);
+}
+
+CONSTCD11
+inline
+days
+operator-(const day& x, const day& y) NOEXCEPT
+{
+    return days{static_cast<days::rep>(static_cast<unsigned>(x)
+                                     - static_cast<unsigned>(y))};
+}
+
+CONSTCD11
+inline
+day
+operator+(const day& x, const days& y) NOEXCEPT
+{
+    return day{static_cast<unsigned>(x) + static_cast<unsigned>(y.count())};
+}
+
+CONSTCD11
+inline
+day
+operator+(const days& x, const day& y) NOEXCEPT
+{
+    return y + x;
+}
+
+CONSTCD11
+inline
+day
+operator-(const day& x, const days& y) NOEXCEPT
+{
+    return x + -y;
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const day& d)
+{
+    date::detail::save_ostream<CharT, Traits> _(os);
+    os.fill('0');
+    os.flags(std::ios::dec | std::ios::right);
+    os.width(2);
+    os << static_cast<unsigned>(d);
+    return os;
+}
+
+// month
+
+CONSTCD11 inline month::month(unsigned m) NOEXCEPT : m_(static_cast<decltype(m_)>(m)) {}
+CONSTCD14 inline month& month::operator++() NOEXCEPT {if (++m_ == 13) m_ = 1; return *this;}
+CONSTCD14 inline month month::operator++(int) NOEXCEPT {auto tmp(*this); ++(*this); return tmp;}
+CONSTCD14 inline month& month::operator--() NOEXCEPT {if (--m_ == 0) m_ = 12; return *this;}
+CONSTCD14 inline month month::operator--(int) NOEXCEPT {auto tmp(*this); --(*this); return tmp;}
+
+CONSTCD14
+inline
+month&
+month::operator+=(const months& m) NOEXCEPT
+{
+    *this = *this + m;
+    return *this;
+}
+
+CONSTCD14
+inline
+month&
+month::operator-=(const months& m) NOEXCEPT
+{
+    *this = *this - m;
+    return *this;
+}
+
+CONSTCD11 inline month::operator unsigned() const NOEXCEPT {return m_;}
+CONSTCD11 inline bool month::ok() const NOEXCEPT {return 1 <= m_ && m_ <= 12;}
+
+CONSTCD11
+inline
+bool
+operator==(const month& x, const month& y) NOEXCEPT
+{
+    return static_cast<unsigned>(x) == static_cast<unsigned>(y);
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const month& x, const month& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+CONSTCD11
+inline
+bool
+operator<(const month& x, const month& y) NOEXCEPT
+{
+    return static_cast<unsigned>(x) < static_cast<unsigned>(y);
+}
+
+CONSTCD11
+inline
+bool
+operator>(const month& x, const month& y) NOEXCEPT
+{
+    return y < x;
+}
+
+CONSTCD11
+inline
+bool
+operator<=(const month& x, const month& y) NOEXCEPT
+{
+    return !(y < x);
+}
+
+CONSTCD11
+inline
+bool
+operator>=(const month& x, const month& y) NOEXCEPT
+{
+    return !(x < y);
+}
+
+CONSTCD14
+inline
+months
+operator-(const month& x, const month& y) NOEXCEPT
+{
+    auto const d = static_cast<unsigned>(x) - static_cast<unsigned>(y);
+    return months(d <= 11 ? d : d + 12);
+}
+
+CONSTCD14
+inline
+month
+operator+(const month& x, const months& y) NOEXCEPT
+{
+    auto const mu = static_cast<long long>(static_cast<unsigned>(x)) - 1 + y.count();
+    auto const yr = (mu >= 0 ? mu : mu-11) / 12;
+    return month{static_cast<unsigned>(mu - yr * 12 + 1)};
+}
+
+CONSTCD14
+inline
+month
+operator+(const months& x, const month& y) NOEXCEPT
+{
+    return y + x;
+}
+
+CONSTCD14
+inline
+month
+operator-(const month& x, const months& y) NOEXCEPT
+{
+    return x + -y;
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const month& m)
+{
+    switch (static_cast<unsigned>(m))
+    {
+    case 1:
+        os << "Jan";
+        break;
+    case 2:
+        os << "Feb";
+        break;
+    case 3:
+        os << "Mar";
+        break;
+    case 4:
+        os << "Apr";
+        break;
+    case 5:
+        os << "May";
+        break;
+    case 6:
+        os << "Jun";
+        break;
+    case 7:
+        os << "Jul";
+        break;
+    case 8:
+        os << "Aug";
+        break;
+    case 9:
+        os << "Sep";
+        break;
+    case 10:
+        os << "Oct";
+        break;
+    case 11:
+        os << "Nov";
+        break;
+    case 12:
+        os << "Dec";
+        break;
+    default:
+        os << static_cast<unsigned>(m) << " is not a valid month";
+        break;
+    }
+    return os;
+}
+
+// year
+
+CONSTCD11 inline year::year(int y) NOEXCEPT : y_(static_cast<decltype(y_)>(y)) {}
+CONSTCD14 inline year& year::operator++() NOEXCEPT {++y_; return *this;}
+CONSTCD14 inline year year::operator++(int) NOEXCEPT {auto tmp(*this); ++(*this); return tmp;}
+CONSTCD14 inline year& year::operator--() NOEXCEPT {--y_; return *this;}
+CONSTCD14 inline year year::operator--(int) NOEXCEPT {auto tmp(*this); --(*this); return tmp;}
+CONSTCD14 inline year& year::operator+=(const years& y) NOEXCEPT {*this = *this + y; return *this;}
+CONSTCD14 inline year& year::operator-=(const years& y) NOEXCEPT {*this = *this - y; return *this;}
+
+CONSTCD11
+inline
+bool
+year::is_leap() const NOEXCEPT
+{
+    return y_ % 4 == 0;
+}
+
+CONSTCD11 inline year::operator int() const NOEXCEPT {return y_;}
+CONSTCD11 inline bool year::ok() const NOEXCEPT {return true;}
+
+CONSTCD11
+inline
+year
+year::min() NOEXCEPT
+{
+    return year{std::numeric_limits<short>::min()};
+}
+
+CONSTCD11
+inline
+year
+year::max() NOEXCEPT
+{
+    return year{std::numeric_limits<short>::max()};
+}
+
+CONSTCD11
+inline
+bool
+operator==(const year& x, const year& y) NOEXCEPT
+{
+    return static_cast<int>(x) == static_cast<int>(y);
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const year& x, const year& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+CONSTCD11
+inline
+bool
+operator<(const year& x, const year& y) NOEXCEPT
+{
+    return static_cast<int>(x) < static_cast<int>(y);
+}
+
+CONSTCD11
+inline
+bool
+operator>(const year& x, const year& y) NOEXCEPT
+{
+    return y < x;
+}
+
+CONSTCD11
+inline
+bool
+operator<=(const year& x, const year& y) NOEXCEPT
+{
+    return !(y < x);
+}
+
+CONSTCD11
+inline
+bool
+operator>=(const year& x, const year& y) NOEXCEPT
+{
+    return !(x < y);
+}
+
+CONSTCD11
+inline
+years
+operator-(const year& x, const year& y) NOEXCEPT
+{
+    return years{static_cast<int>(x) - static_cast<int>(y)};
+}
+
+CONSTCD11
+inline
+year
+operator+(const year& x, const years& y) NOEXCEPT
+{
+    return year{static_cast<int>(x) + y.count()};
+}
+
+CONSTCD11
+inline
+year
+operator+(const years& x, const year& y) NOEXCEPT
+{
+    return y + x;
+}
+
+CONSTCD11
+inline
+year
+operator-(const year& x, const years& y) NOEXCEPT
+{
+    return year{static_cast<int>(x) - y.count()};
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year& y)
+{
+    date::detail::save_ostream<CharT, Traits> _(os);
+    os.fill('0');
+    os.flags(std::ios::dec | std::ios::internal);
+    os.width(4 + (y < year{0}));
+    os << static_cast<int>(y);
+    return os;
+}
+
+// weekday
+
+CONSTCD11
+inline
+unsigned char
+weekday::weekday_from_days(int z) NOEXCEPT
+{
+    return static_cast<unsigned char>(static_cast<unsigned>(
+        z >= -4 ? (z+4) % 7 : (z+5) % 7 + 6));
+}
+
+CONSTCD11
+inline
+weekday::weekday(unsigned wd) NOEXCEPT
+    : wd_(static_cast<decltype(wd_)>(wd))
+    {}
+
+CONSTCD11
+inline
+weekday::weekday(const sys_days& dp) NOEXCEPT
+    : wd_(weekday_from_days(dp.time_since_epoch().count()))
+    {}
+
+CONSTCD11
+inline
+weekday::weekday(const local_days& dp) NOEXCEPT
+    : wd_(weekday_from_days(dp.time_since_epoch().count()))
+    {}
+
+CONSTCD14 inline weekday& weekday::operator++() NOEXCEPT {if (++wd_ == 7) wd_ = 0; return *this;}
+CONSTCD14 inline weekday weekday::operator++(int) NOEXCEPT {auto tmp(*this); ++(*this); return tmp;}
+CONSTCD14 inline weekday& weekday::operator--() NOEXCEPT {if (wd_-- == 0) wd_ = 6; return *this;}
+CONSTCD14 inline weekday weekday::operator--(int) NOEXCEPT {auto tmp(*this); --(*this); return tmp;}
+
+CONSTCD14
+inline
+weekday&
+weekday::operator+=(const days& d) NOEXCEPT
+{
+    *this = *this + d;
+    return *this;
+}
+
+CONSTCD14
+inline
+weekday&
+weekday::operator-=(const days& d) NOEXCEPT
+{
+    *this = *this - d;
+    return *this;
+}
+
+CONSTCD11
+inline
+weekday::operator unsigned() const NOEXCEPT
+{
+    return static_cast<unsigned>(wd_);
+}
+
+CONSTCD11 inline bool weekday::ok() const NOEXCEPT {return wd_ <= 6;}
+
+CONSTCD11
+inline
+bool
+operator==(const weekday& x, const weekday& y) NOEXCEPT
+{
+    return static_cast<unsigned>(x) == static_cast<unsigned>(y);
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const weekday& x, const weekday& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+CONSTCD14
+inline
+days
+operator-(const weekday& x, const weekday& y) NOEXCEPT
+{
+    auto const diff = static_cast<unsigned>(x) - static_cast<unsigned>(y);
+    return days{diff <= 6 ? diff : diff + 7};
+}
+
+CONSTCD14
+inline
+weekday
+operator+(const weekday& x, const days& y) NOEXCEPT
+{
+    auto const wdu = static_cast<long long>(static_cast<unsigned>(x)) + y.count();
+    auto const wk = (wdu >= 0 ? wdu : wdu-6) / 7;
+    return weekday{static_cast<unsigned>(wdu - wk * 7)};
+}
+
+CONSTCD14
+inline
+weekday
+operator+(const days& x, const weekday& y) NOEXCEPT
+{
+    return y + x;
+}
+
+CONSTCD14
+inline
+weekday
+operator-(const weekday& x, const days& y) NOEXCEPT
+{
+    return x + -y;
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const weekday& wd)
+{
+    switch (static_cast<unsigned>(wd))
+    {
+    case 0:
+        os << "Sun";
+        break;
+    case 1:
+        os << "Mon";
+        break;
+    case 2:
+        os << "Tue";
+        break;
+    case 3:
+        os << "Wed";
+        break;
+    case 4:
+        os << "Thu";
+        break;
+    case 5:
+        os << "Fri";
+        break;
+    case 6:
+        os << "Sat";
+        break;
+    default:
+        os << static_cast<unsigned>(wd) << " is not a valid weekday";
+        break;
+    }
+    return os;
+}
+
+#if !defined(_MSC_VER) || (_MSC_VER >= 1900)
+inline namespace literals
+{
+
+CONSTCD11
+inline
+julian::day
+operator "" _d(unsigned long long d) NOEXCEPT
+{
+    return julian::day{static_cast<unsigned>(d)};
+}
+
+CONSTCD11
+inline
+julian::year
+operator "" _y(unsigned long long y) NOEXCEPT
+{
+    return julian::year(static_cast<int>(y));
+}
+#endif  // !defined(_MSC_VER) || (_MSC_VER >= 1900)
+
+CONSTDATA julian::last_spec last{};
+
+CONSTDATA julian::month jan{1};
+CONSTDATA julian::month feb{2};
+CONSTDATA julian::month mar{3};
+CONSTDATA julian::month apr{4};
+CONSTDATA julian::month may{5};
+CONSTDATA julian::month jun{6};
+CONSTDATA julian::month jul{7};
+CONSTDATA julian::month aug{8};
+CONSTDATA julian::month sep{9};
+CONSTDATA julian::month oct{10};
+CONSTDATA julian::month nov{11};
+CONSTDATA julian::month dec{12};
+
+CONSTDATA julian::weekday sun{0u};
+CONSTDATA julian::weekday mon{1u};
+CONSTDATA julian::weekday tue{2u};
+CONSTDATA julian::weekday wed{3u};
+CONSTDATA julian::weekday thu{4u};
+CONSTDATA julian::weekday fri{5u};
+CONSTDATA julian::weekday sat{6u};
+
+#if !defined(_MSC_VER) || (_MSC_VER >= 1900)
+}  // inline namespace literals
+#endif
+
+// weekday_indexed
+
+CONSTCD11
+inline
+weekday
+weekday_indexed::weekday() const NOEXCEPT
+{
+    return julian::weekday{static_cast<unsigned>(wd_)};
+}
+
+CONSTCD11 inline unsigned weekday_indexed::index() const NOEXCEPT {return index_;}
+
+CONSTCD11
+inline
+bool
+weekday_indexed::ok() const NOEXCEPT
+{
+    return weekday().ok() && 1 <= index_ && index_ <= 5;
+}
+
+CONSTCD11
+inline
+weekday_indexed::weekday_indexed(const julian::weekday& wd, unsigned index) NOEXCEPT
+    : wd_(static_cast<decltype(wd_)>(static_cast<unsigned>(wd)))
+    , index_(static_cast<decltype(index_)>(index))
+    {}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const weekday_indexed& wdi)
+{
+    return os << wdi.weekday() << '[' << wdi.index() << ']';
+}
+
+CONSTCD11
+inline
+weekday_indexed
+weekday::operator[](unsigned index) const NOEXCEPT
+{
+    return {*this, index};
+}
+
+CONSTCD11
+inline
+bool
+operator==(const weekday_indexed& x, const weekday_indexed& y) NOEXCEPT
+{
+    return x.weekday() == y.weekday() && x.index() == y.index();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const weekday_indexed& x, const weekday_indexed& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+// weekday_last
+
+CONSTCD11 inline julian::weekday weekday_last::weekday() const NOEXCEPT {return wd_;}
+CONSTCD11 inline bool weekday_last::ok() const NOEXCEPT {return wd_.ok();}
+CONSTCD11 inline weekday_last::weekday_last(const julian::weekday& wd) NOEXCEPT : wd_(wd) {}
+
+CONSTCD11
+inline
+bool
+operator==(const weekday_last& x, const weekday_last& y) NOEXCEPT
+{
+    return x.weekday() == y.weekday();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const weekday_last& x, const weekday_last& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const weekday_last& wdl)
+{
+    return os << wdl.weekday() << "[last]";
+}
+
+CONSTCD11
+inline
+weekday_last
+weekday::operator[](last_spec) const NOEXCEPT
+{
+    return weekday_last{*this};
+}
+
+// year_month
+
+CONSTCD11
+inline
+year_month::year_month(const julian::year& y, const julian::month& m) NOEXCEPT
+    : y_(y)
+    , m_(m)
+    {}
+
+CONSTCD11 inline year year_month::year() const NOEXCEPT {return y_;}
+CONSTCD11 inline month year_month::month() const NOEXCEPT {return m_;}
+CONSTCD11 inline bool year_month::ok() const NOEXCEPT {return y_.ok() && m_.ok();}
+
+CONSTCD14
+inline
+year_month&
+year_month::operator+=(const months& dm) NOEXCEPT
+{
+    *this = *this + dm;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month&
+year_month::operator-=(const months& dm) NOEXCEPT
+{
+    *this = *this - dm;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month&
+year_month::operator+=(const years& dy) NOEXCEPT
+{
+    *this = *this + dy;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month&
+year_month::operator-=(const years& dy) NOEXCEPT
+{
+    *this = *this - dy;
+    return *this;
+}
+
+CONSTCD11
+inline
+bool
+operator==(const year_month& x, const year_month& y) NOEXCEPT
+{
+    return x.year() == y.year() && x.month() == y.month();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const year_month& x, const year_month& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+CONSTCD11
+inline
+bool
+operator<(const year_month& x, const year_month& y) NOEXCEPT
+{
+    return x.year() < y.year() ? true
+        : (x.year() > y.year() ? false
+        : (x.month() < y.month()));
+}
+
+CONSTCD11
+inline
+bool
+operator>(const year_month& x, const year_month& y) NOEXCEPT
+{
+    return y < x;
+}
+
+CONSTCD11
+inline
+bool
+operator<=(const year_month& x, const year_month& y) NOEXCEPT
+{
+    return !(y < x);
+}
+
+CONSTCD11
+inline
+bool
+operator>=(const year_month& x, const year_month& y) NOEXCEPT
+{
+    return !(x < y);
+}
+
+CONSTCD14
+inline
+year_month
+operator+(const year_month& ym, const months& dm) NOEXCEPT
+{
+    auto dmi = static_cast<int>(static_cast<unsigned>(ym.month())) - 1 + dm.count();
+    auto dy = (dmi >= 0 ? dmi : dmi-11) / 12;
+    dmi = dmi - dy * 12 + 1;
+    return (ym.year() + years(dy)) / month(static_cast<unsigned>(dmi));
+}
+
+CONSTCD14
+inline
+year_month
+operator+(const months& dm, const year_month& ym) NOEXCEPT
+{
+    return ym + dm;
+}
+
+CONSTCD14
+inline
+year_month
+operator-(const year_month& ym, const months& dm) NOEXCEPT
+{
+    return ym + -dm;
+}
+
+CONSTCD11
+inline
+months
+operator-(const year_month& x, const year_month& y) NOEXCEPT
+{
+    return (x.year() - y.year()) +
+            months(static_cast<unsigned>(x.month()) - static_cast<unsigned>(y.month()));
+}
+
+CONSTCD11
+inline
+year_month
+operator+(const year_month& ym, const years& dy) NOEXCEPT
+{
+    return (ym.year() + dy) / ym.month();
+}
+
+CONSTCD11
+inline
+year_month
+operator+(const years& dy, const year_month& ym) NOEXCEPT
+{
+    return ym + dy;
+}
+
+CONSTCD11
+inline
+year_month
+operator-(const year_month& ym, const years& dy) NOEXCEPT
+{
+    return ym + -dy;
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_month& ym)
+{
+    return os << ym.year() << '/' << ym.month();
+}
+
+// month_day
+
+CONSTCD11
+inline
+month_day::month_day(const julian::month& m, const julian::day& d) NOEXCEPT
+    : m_(m)
+    , d_(d)
+    {}
+
+CONSTCD11 inline julian::month month_day::month() const NOEXCEPT {return m_;}
+CONSTCD11 inline julian::day month_day::day() const NOEXCEPT {return d_;}
+
+CONSTCD14
+inline
+bool
+month_day::ok() const NOEXCEPT
+{
+    CONSTDATA julian::day d[] = { 
+        julian::day(31), julian::day(29), julian::day(31), julian::day(30), 
+        julian::day(31), julian::day(30), julian::day(31), julian::day(31), 
+        julian::day(30), julian::day(31), julian::day(30), julian::day(31) 
+    };
+    return m_.ok() && julian::day(1) <= d_ && d_ <= d[static_cast<unsigned>(m_)-1];
+}
+
+CONSTCD11
+inline
+bool
+operator==(const month_day& x, const month_day& y) NOEXCEPT
+{
+    return x.month() == y.month() && x.day() == y.day();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const month_day& x, const month_day& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+CONSTCD11
+inline
+bool
+operator<(const month_day& x, const month_day& y) NOEXCEPT
+{
+    return x.month() < y.month() ? true
+        : (x.month() > y.month() ? false
+        : (x.day() < y.day()));
+}
+
+CONSTCD11
+inline
+bool
+operator>(const month_day& x, const month_day& y) NOEXCEPT
+{
+    return y < x;
+}
+
+CONSTCD11
+inline
+bool
+operator<=(const month_day& x, const month_day& y) NOEXCEPT
+{
+    return !(y < x);
+}
+
+CONSTCD11
+inline
+bool
+operator>=(const month_day& x, const month_day& y) NOEXCEPT
+{
+    return !(x < y);
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const month_day& md)
+{
+    return os << md.month() << '/' << md.day();
+}
+
+// month_day_last
+
+CONSTCD11 inline month month_day_last::month() const NOEXCEPT {return m_;}
+CONSTCD11 inline bool month_day_last::ok() const NOEXCEPT {return m_.ok();}
+CONSTCD11 inline month_day_last::month_day_last(const julian::month& m) NOEXCEPT : m_(m) {}
+
+CONSTCD11
+inline
+bool
+operator==(const month_day_last& x, const month_day_last& y) NOEXCEPT
+{
+    return x.month() == y.month();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const month_day_last& x, const month_day_last& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+CONSTCD11
+inline
+bool
+operator<(const month_day_last& x, const month_day_last& y) NOEXCEPT
+{
+    return x.month() < y.month();
+}
+
+CONSTCD11
+inline
+bool
+operator>(const month_day_last& x, const month_day_last& y) NOEXCEPT
+{
+    return y < x;
+}
+
+CONSTCD11
+inline
+bool
+operator<=(const month_day_last& x, const month_day_last& y) NOEXCEPT
+{
+    return !(y < x);
+}
+
+CONSTCD11
+inline
+bool
+operator>=(const month_day_last& x, const month_day_last& y) NOEXCEPT
+{
+    return !(x < y);
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const month_day_last& mdl)
+{
+    return os << mdl.month() << "/last";
+}
+
+// month_weekday
+
+CONSTCD11
+inline
+month_weekday::month_weekday(const julian::month& m,
+                             const julian::weekday_indexed& wdi) NOEXCEPT
+    : m_(m)
+    , wdi_(wdi)
+    {}
+
+CONSTCD11 inline month month_weekday::month() const NOEXCEPT {return m_;}
+
+CONSTCD11
+inline
+weekday_indexed
+month_weekday::weekday_indexed() const NOEXCEPT
+{
+    return wdi_;
+}
+
+CONSTCD11
+inline
+bool
+month_weekday::ok() const NOEXCEPT
+{
+    return m_.ok() && wdi_.ok();
+}
+
+CONSTCD11
+inline
+bool
+operator==(const month_weekday& x, const month_weekday& y) NOEXCEPT
+{
+    return x.month() == y.month() && x.weekday_indexed() == y.weekday_indexed();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const month_weekday& x, const month_weekday& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const month_weekday& mwd)
+{
+    return os << mwd.month() << '/' << mwd.weekday_indexed();
+}
+
+// month_weekday_last
+
+CONSTCD11
+inline
+month_weekday_last::month_weekday_last(const julian::month& m,
+                                       const julian::weekday_last& wdl) NOEXCEPT
+    : m_(m)
+    , wdl_(wdl)
+    {}
+
+CONSTCD11 inline month month_weekday_last::month() const NOEXCEPT {return m_;}
+
+CONSTCD11
+inline
+weekday_last
+month_weekday_last::weekday_last() const NOEXCEPT
+{
+    return wdl_;
+}
+
+CONSTCD11
+inline
+bool
+month_weekday_last::ok() const NOEXCEPT
+{
+    return m_.ok() && wdl_.ok();
+}
+
+CONSTCD11
+inline
+bool
+operator==(const month_weekday_last& x, const month_weekday_last& y) NOEXCEPT
+{
+    return x.month() == y.month() && x.weekday_last() == y.weekday_last();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const month_weekday_last& x, const month_weekday_last& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const month_weekday_last& mwdl)
+{
+    return os << mwdl.month() << '/' << mwdl.weekday_last();
+}
+
+// year_month_day_last
+
+CONSTCD11
+inline
+year_month_day_last::year_month_day_last(const julian::year& y,
+                                         const julian::month_day_last& mdl) NOEXCEPT
+    : y_(y)
+    , mdl_(mdl)
+    {}
+
+CONSTCD14
+inline
+year_month_day_last&
+year_month_day_last::operator+=(const months& m) NOEXCEPT
+{
+    *this = *this + m;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month_day_last&
+year_month_day_last::operator-=(const months& m) NOEXCEPT
+{
+    *this = *this - m;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month_day_last&
+year_month_day_last::operator+=(const years& y) NOEXCEPT
+{
+    *this = *this + y;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month_day_last&
+year_month_day_last::operator-=(const years& y) NOEXCEPT
+{
+    *this = *this - y;
+    return *this;
+}
+
+CONSTCD11 inline year year_month_day_last::year() const NOEXCEPT {return y_;}
+CONSTCD11 inline month year_month_day_last::month() const NOEXCEPT {return mdl_.month();}
+
+CONSTCD11
+inline
+month_day_last
+year_month_day_last::month_day_last() const NOEXCEPT
+{
+    return mdl_;
+}
+
+CONSTCD14
+inline
+day
+year_month_day_last::day() const NOEXCEPT
+{
+    CONSTDATA julian::day d[] = { 
+        julian::day(31), julian::day(28), julian::day(31), julian::day(30), 
+        julian::day(31), julian::day(30), julian::day(31), julian::day(31), 
+        julian::day(30), julian::day(31), julian::day(30), julian::day(31) 
+    };
+    return month() != feb || !y_.is_leap() ? d[static_cast<unsigned>(month())-1] : julian::day(29);
+}
+
+CONSTCD14
+inline
+year_month_day_last::operator sys_days() const NOEXCEPT
+{
+    return sys_days(year()/month()/day());
+}
+
+CONSTCD14
+inline
+year_month_day_last::operator local_days() const NOEXCEPT
+{
+    return local_days(year()/month()/day());
+}
+
+CONSTCD11
+inline
+bool
+year_month_day_last::ok() const NOEXCEPT
+{
+    return y_.ok() && mdl_.ok();
+}
+
+CONSTCD11
+inline
+bool
+operator==(const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT
+{
+    return x.year() == y.year() && x.month_day_last() == y.month_day_last();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+CONSTCD11
+inline
+bool
+operator<(const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT
+{
+    return x.year() < y.year() ? true
+        : (x.year() > y.year() ? false
+        : (x.month_day_last() < y.month_day_last()));
+}
+
+CONSTCD11
+inline
+bool
+operator>(const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT
+{
+    return y < x;
+}
+
+CONSTCD11
+inline
+bool
+operator<=(const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT
+{
+    return !(y < x);
+}
+
+CONSTCD11
+inline
+bool
+operator>=(const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT
+{
+    return !(x < y);
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_month_day_last& ymdl)
+{
+    return os << ymdl.year() << '/' << ymdl.month_day_last();
+}
+
+CONSTCD14
+inline
+year_month_day_last
+operator+(const year_month_day_last& ymdl, const months& dm) NOEXCEPT
+{
+    return (ymdl.year() / ymdl.month() + dm) / last;
+}
+
+CONSTCD14
+inline
+year_month_day_last
+operator+(const months& dm, const year_month_day_last& ymdl) NOEXCEPT
+{
+    return ymdl + dm;
+}
+
+CONSTCD14
+inline
+year_month_day_last
+operator-(const year_month_day_last& ymdl, const months& dm) NOEXCEPT
+{
+    return ymdl + (-dm);
+}
+
+CONSTCD11
+inline
+year_month_day_last
+operator+(const year_month_day_last& ymdl, const years& dy) NOEXCEPT
+{
+    return {ymdl.year()+dy, ymdl.month_day_last()};
+}
+
+CONSTCD11
+inline
+year_month_day_last
+operator+(const years& dy, const year_month_day_last& ymdl) NOEXCEPT
+{
+    return ymdl + dy;
+}
+
+CONSTCD11
+inline
+year_month_day_last
+operator-(const year_month_day_last& ymdl, const years& dy) NOEXCEPT
+{
+    return ymdl + (-dy);
+}
+
+// year_month_day
+
+CONSTCD11
+inline
+year_month_day::year_month_day(const julian::year& y, const julian::month& m,
+                               const julian::day& d) NOEXCEPT
+    : y_(y)
+    , m_(m)
+    , d_(d)
+    {}
+
+CONSTCD14
+inline
+year_month_day::year_month_day(const year_month_day_last& ymdl) NOEXCEPT
+    : y_(ymdl.year())
+    , m_(ymdl.month())
+    , d_(ymdl.day())
+    {}
+
+CONSTCD14
+inline
+year_month_day::year_month_day(sys_days dp) NOEXCEPT
+    : year_month_day(from_days(dp.time_since_epoch()))
+    {}
+
+CONSTCD14
+inline
+year_month_day::year_month_day(local_days dp) NOEXCEPT
+    : year_month_day(from_days(dp.time_since_epoch()))
+    {}
+
+CONSTCD11 inline year year_month_day::year() const NOEXCEPT {return y_;}
+CONSTCD11 inline month year_month_day::month() const NOEXCEPT {return m_;}
+CONSTCD11 inline day year_month_day::day() const NOEXCEPT {return d_;}
+
+CONSTCD14
+inline
+year_month_day&
+year_month_day::operator+=(const months& m) NOEXCEPT
+{
+    *this = *this + m;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month_day&
+year_month_day::operator-=(const months& m) NOEXCEPT
+{
+    *this = *this - m;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month_day&
+year_month_day::operator+=(const years& y) NOEXCEPT
+{
+    *this = *this + y;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month_day&
+year_month_day::operator-=(const years& y) NOEXCEPT
+{
+    *this = *this - y;
+    return *this;
+}
+
+CONSTCD14
+inline
+days
+year_month_day::to_days() const NOEXCEPT
+{
+    static_assert(std::numeric_limits<unsigned>::digits >= 18,
+             "This algorithm has not been ported to a 16 bit unsigned integer");
+    static_assert(std::numeric_limits<int>::digits >= 20,
+             "This algorithm has not been ported to a 16 bit signed integer");
+    auto const y = static_cast<int>(y_) - (m_ <= feb);
+    auto const m = static_cast<unsigned>(m_);
+    auto const d = static_cast<unsigned>(d_);
+    auto const era = (y >= 0 ? y : y-3) / 4;
+    auto const yoe = static_cast<unsigned>(y - era * 4);       // [0, 3]
+    auto const doy = (153*(m > 2 ? m-3 : m+9) + 2)/5 + d-1;    // [0, 365]
+    auto const doe = yoe * 365 + doy;                          // [0, 1460]
+    return days{era * 1461 + static_cast<int>(doe) - 719470};
+}
+
+CONSTCD14
+inline
+year_month_day::operator sys_days() const NOEXCEPT
+{
+    return sys_days{to_days()};
+}
+
+CONSTCD14
+inline
+year_month_day::operator local_days() const NOEXCEPT
+{
+    return local_days{to_days()};
+}
+
+CONSTCD14
+inline
+bool
+year_month_day::ok() const NOEXCEPT
+{
+    if (!(y_.ok() && m_.ok()))
+        return false;
+    return julian::day(1) <= d_ && d_ <= (y_/m_/last).day();
+}
+
+CONSTCD11
+inline
+bool
+operator==(const year_month_day& x, const year_month_day& y) NOEXCEPT
+{
+    return x.year() == y.year() && x.month() == y.month() && x.day() == y.day();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const year_month_day& x, const year_month_day& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+CONSTCD11
+inline
+bool
+operator<(const year_month_day& x, const year_month_day& y) NOEXCEPT
+{
+    return x.year() < y.year() ? true
+        : (x.year() > y.year() ? false
+        : (x.month() < y.month() ? true
+        : (x.month() > y.month() ? false
+        : (x.day() < y.day()))));
+}
+
+CONSTCD11
+inline
+bool
+operator>(const year_month_day& x, const year_month_day& y) NOEXCEPT
+{
+    return y < x;
+}
+
+CONSTCD11
+inline
+bool
+operator<=(const year_month_day& x, const year_month_day& y) NOEXCEPT
+{
+    return !(y < x);
+}
+
+CONSTCD11
+inline
+bool
+operator>=(const year_month_day& x, const year_month_day& y) NOEXCEPT
+{
+    return !(x < y);
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_month_day& ymd)
+{
+    date::detail::save_ostream<CharT, Traits> _(os);
+    os.fill('0');
+    os.flags(std::ios::dec | std::ios::right);
+    os << ymd.year() << '-';
+    os.width(2);
+    os << static_cast<unsigned>(ymd.month()) << '-';
+    os << ymd.day();
+    return os;
+}
+
+CONSTCD14
+inline
+year_month_day
+year_month_day::from_days(days dp) NOEXCEPT
+{
+    static_assert(std::numeric_limits<unsigned>::digits >= 18,
+             "This algorithm has not been ported to a 16 bit unsigned integer");
+    static_assert(std::numeric_limits<int>::digits >= 20,
+             "This algorithm has not been ported to a 16 bit signed integer");
+    auto const z = dp.count() + 719470;
+    auto const era = (z >= 0 ? z : z - 1460) / 1461;
+    auto const doe = static_cast<unsigned>(z - era * 1461);          // [0, 1460]
+    auto const yoe = (doe - doe/1460) / 365;                         // [0, 3]
+    auto const y = static_cast<sys_days::rep>(yoe) + era * 4;
+    auto const doy = doe - 365*yoe;                                  // [0, 365]
+    auto const mp = (5*doy + 2)/153;                                 // [0, 11]
+    auto const d = doy - (153*mp+2)/5 + 1;                           // [1, 31]
+    auto const m = mp < 10 ? mp+3 : mp-9;                            // [1, 12]
+    return year_month_day{julian::year{y + (m <= 2)}, julian::month(m), julian::day(d)};
+}
+
+CONSTCD14
+inline
+year_month_day
+operator+(const year_month_day& ymd, const months& dm) NOEXCEPT
+{
+    return (ymd.year() / ymd.month() + dm) / ymd.day();
+}
+
+CONSTCD14
+inline
+year_month_day
+operator+(const months& dm, const year_month_day& ymd) NOEXCEPT
+{
+    return ymd + dm;
+}
+
+CONSTCD14
+inline
+year_month_day
+operator-(const year_month_day& ymd, const months& dm) NOEXCEPT
+{
+    return ymd + (-dm);
+}
+
+CONSTCD11
+inline
+year_month_day
+operator+(const year_month_day& ymd, const years& dy) NOEXCEPT
+{
+    return (ymd.year() + dy) / ymd.month() / ymd.day();
+}
+
+CONSTCD11
+inline
+year_month_day
+operator+(const years& dy, const year_month_day& ymd) NOEXCEPT
+{
+    return ymd + dy;
+}
+
+CONSTCD11
+inline
+year_month_day
+operator-(const year_month_day& ymd, const years& dy) NOEXCEPT
+{
+    return ymd + (-dy);
+}
+
+// year_month_weekday
+
+CONSTCD11
+inline
+year_month_weekday::year_month_weekday(const julian::year& y, const julian::month& m,
+                                       const julian::weekday_indexed& wdi)
+        NOEXCEPT
+    : y_(y)
+    , m_(m)
+    , wdi_(wdi)
+    {}
+
+CONSTCD14
+inline
+year_month_weekday::year_month_weekday(const sys_days& dp) NOEXCEPT
+    : year_month_weekday(from_days(dp.time_since_epoch()))
+    {}
+
+CONSTCD14
+inline
+year_month_weekday::year_month_weekday(const local_days& dp) NOEXCEPT
+    : year_month_weekday(from_days(dp.time_since_epoch()))
+    {}
+
+CONSTCD14
+inline
+year_month_weekday&
+year_month_weekday::operator+=(const months& m) NOEXCEPT
+{
+    *this = *this + m;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month_weekday&
+year_month_weekday::operator-=(const months& m) NOEXCEPT
+{
+    *this = *this - m;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month_weekday&
+year_month_weekday::operator+=(const years& y) NOEXCEPT
+{
+    *this = *this + y;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month_weekday&
+year_month_weekday::operator-=(const years& y) NOEXCEPT
+{
+    *this = *this - y;
+    return *this;
+}
+
+CONSTCD11 inline year year_month_weekday::year() const NOEXCEPT {return y_;}
+CONSTCD11 inline month year_month_weekday::month() const NOEXCEPT {return m_;}
+
+CONSTCD11
+inline
+weekday
+year_month_weekday::weekday() const NOEXCEPT
+{
+    return wdi_.weekday();
+}
+
+CONSTCD11
+inline
+unsigned
+year_month_weekday::index() const NOEXCEPT
+{
+    return wdi_.index();
+}
+
+CONSTCD11
+inline
+weekday_indexed
+year_month_weekday::weekday_indexed() const NOEXCEPT
+{
+    return wdi_;
+}
+
+CONSTCD14
+inline
+year_month_weekday::operator sys_days() const NOEXCEPT
+{
+    return sys_days{to_days()};
+}
+
+CONSTCD14
+inline
+year_month_weekday::operator local_days() const NOEXCEPT
+{
+    return local_days{to_days()};
+}
+
+CONSTCD14
+inline
+bool
+year_month_weekday::ok() const NOEXCEPT
+{
+    if (!y_.ok() || !m_.ok() || !wdi_.weekday().ok() || wdi_.index() < 1)
+        return false;
+    if (wdi_.index() <= 4)
+        return true;
+    auto d2 = wdi_.weekday() - julian::weekday(y_/m_/1) + days((wdi_.index()-1)*7 + 1);
+    return static_cast<unsigned>(d2.count()) <= static_cast<unsigned>((y_/m_/last).day());
+}
+
+CONSTCD14
+inline
+year_month_weekday
+year_month_weekday::from_days(days d) NOEXCEPT
+{
+    sys_days dp{d};
+    auto const wd = julian::weekday(dp);
+    auto const ymd = year_month_day(dp);
+    return {ymd.year(), ymd.month(), wd[(static_cast<unsigned>(ymd.day())-1)/7+1]};
+}
+
+CONSTCD14
+inline
+days
+year_month_weekday::to_days() const NOEXCEPT
+{
+    auto d = sys_days(y_/m_/1);
+    return (d + (wdi_.weekday() - julian::weekday(d) + days{(wdi_.index()-1)*7})
+           ).time_since_epoch();
+}
+
+CONSTCD11
+inline
+bool
+operator==(const year_month_weekday& x, const year_month_weekday& y) NOEXCEPT
+{
+    return x.year() == y.year() && x.month() == y.month() &&
+           x.weekday_indexed() == y.weekday_indexed();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const year_month_weekday& x, const year_month_weekday& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_month_weekday& ymwdi)
+{
+    return os << ymwdi.year() << '/' << ymwdi.month()
+              << '/' << ymwdi.weekday_indexed();
+}
+
+CONSTCD14
+inline
+year_month_weekday
+operator+(const year_month_weekday& ymwd, const months& dm) NOEXCEPT
+{
+    return (ymwd.year() / ymwd.month() + dm) / ymwd.weekday_indexed();
+}
+
+CONSTCD14
+inline
+year_month_weekday
+operator+(const months& dm, const year_month_weekday& ymwd) NOEXCEPT
+{
+    return ymwd + dm;
+}
+
+CONSTCD14
+inline
+year_month_weekday
+operator-(const year_month_weekday& ymwd, const months& dm) NOEXCEPT
+{
+    return ymwd + (-dm);
+}
+
+CONSTCD11
+inline
+year_month_weekday
+operator+(const year_month_weekday& ymwd, const years& dy) NOEXCEPT
+{
+    return {ymwd.year()+dy, ymwd.month(), ymwd.weekday_indexed()};
+}
+
+CONSTCD11
+inline
+year_month_weekday
+operator+(const years& dy, const year_month_weekday& ymwd) NOEXCEPT
+{
+    return ymwd + dy;
+}
+
+CONSTCD11
+inline
+year_month_weekday
+operator-(const year_month_weekday& ymwd, const years& dy) NOEXCEPT
+{
+    return ymwd + (-dy);
+}
+
+// year_month_weekday_last
+
+CONSTCD11
+inline
+year_month_weekday_last::year_month_weekday_last(const julian::year& y,
+                                                 const julian::month& m,
+                                                 const julian::weekday_last& wdl) NOEXCEPT
+    : y_(y)
+    , m_(m)
+    , wdl_(wdl)
+    {}
+
+CONSTCD14
+inline
+year_month_weekday_last&
+year_month_weekday_last::operator+=(const months& m) NOEXCEPT
+{
+    *this = *this + m;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month_weekday_last&
+year_month_weekday_last::operator-=(const months& m) NOEXCEPT
+{
+    *this = *this - m;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month_weekday_last&
+year_month_weekday_last::operator+=(const years& y) NOEXCEPT
+{
+    *this = *this + y;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month_weekday_last&
+year_month_weekday_last::operator-=(const years& y) NOEXCEPT
+{
+    *this = *this - y;
+    return *this;
+}
+
+CONSTCD11 inline year year_month_weekday_last::year() const NOEXCEPT {return y_;}
+CONSTCD11 inline month year_month_weekday_last::month() const NOEXCEPT {return m_;}
+
+CONSTCD11
+inline
+weekday
+year_month_weekday_last::weekday() const NOEXCEPT
+{
+    return wdl_.weekday();
+}
+
+CONSTCD11
+inline
+weekday_last
+year_month_weekday_last::weekday_last() const NOEXCEPT
+{
+    return wdl_;
+}
+
+CONSTCD14
+inline
+year_month_weekday_last::operator sys_days() const NOEXCEPT
+{
+    return sys_days{to_days()};
+}
+
+CONSTCD14
+inline
+year_month_weekday_last::operator local_days() const NOEXCEPT
+{
+    return local_days{to_days()};
+}
+
+CONSTCD11
+inline
+bool
+year_month_weekday_last::ok() const NOEXCEPT
+{
+    return y_.ok() && m_.ok() && wdl_.ok();
+}
+
+CONSTCD14
+inline
+days
+year_month_weekday_last::to_days() const NOEXCEPT
+{
+    auto const d = sys_days(y_/m_/last);
+    return (d - (julian::weekday{d} - wdl_.weekday())).time_since_epoch();
+}
+
+CONSTCD11
+inline
+bool
+operator==(const year_month_weekday_last& x, const year_month_weekday_last& y) NOEXCEPT
+{
+    return x.year() == y.year() && x.month() == y.month() &&
+           x.weekday_last() == y.weekday_last();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const year_month_weekday_last& x, const year_month_weekday_last& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_month_weekday_last& ymwdl)
+{
+    return os << ymwdl.year() << '/' << ymwdl.month() << '/' << ymwdl.weekday_last();
+}
+
+CONSTCD14
+inline
+year_month_weekday_last
+operator+(const year_month_weekday_last& ymwdl, const months& dm) NOEXCEPT
+{
+    return (ymwdl.year() / ymwdl.month() + dm) / ymwdl.weekday_last();
+}
+
+CONSTCD14
+inline
+year_month_weekday_last
+operator+(const months& dm, const year_month_weekday_last& ymwdl) NOEXCEPT
+{
+    return ymwdl + dm;
+}
+
+CONSTCD14
+inline
+year_month_weekday_last
+operator-(const year_month_weekday_last& ymwdl, const months& dm) NOEXCEPT
+{
+    return ymwdl + (-dm);
+}
+
+CONSTCD11
+inline
+year_month_weekday_last
+operator+(const year_month_weekday_last& ymwdl, const years& dy) NOEXCEPT
+{
+    return {ymwdl.year()+dy, ymwdl.month(), ymwdl.weekday_last()};
+}
+
+CONSTCD11
+inline
+year_month_weekday_last
+operator+(const years& dy, const year_month_weekday_last& ymwdl) NOEXCEPT
+{
+    return ymwdl + dy;
+}
+
+CONSTCD11
+inline
+year_month_weekday_last
+operator-(const year_month_weekday_last& ymwdl, const years& dy) NOEXCEPT
+{
+    return ymwdl + (-dy);
+}
+
+// year_month from operator/()
+
+CONSTCD11
+inline
+year_month
+operator/(const year& y, const month& m) NOEXCEPT
+{
+    return {y, m};
+}
+
+CONSTCD11
+inline
+year_month
+operator/(const year& y, int   m) NOEXCEPT
+{
+    return y / month(static_cast<unsigned>(m));
+}
+
+// month_day from operator/()
+
+CONSTCD11
+inline
+month_day
+operator/(const month& m, const day& d) NOEXCEPT
+{
+    return {m, d};
+}
+
+CONSTCD11
+inline
+month_day
+operator/(const day& d, const month& m) NOEXCEPT
+{
+    return m / d;
+}
+
+CONSTCD11
+inline
+month_day
+operator/(const month& m, int d) NOEXCEPT
+{
+    return m / day(static_cast<unsigned>(d));
+}
+
+CONSTCD11
+inline
+month_day
+operator/(int m, const day& d) NOEXCEPT
+{
+    return month(static_cast<unsigned>(m)) / d;
+}
+
+CONSTCD11 inline month_day operator/(const day& d, int m) NOEXCEPT {return m / d;}
+
+// month_day_last from operator/()
+
+CONSTCD11
+inline
+month_day_last
+operator/(const month& m, last_spec) NOEXCEPT
+{
+    return month_day_last{m};
+}
+
+CONSTCD11
+inline
+month_day_last
+operator/(last_spec, const month& m) NOEXCEPT
+{
+    return m/last;
+}
+
+CONSTCD11
+inline
+month_day_last
+operator/(int m, last_spec) NOEXCEPT
+{
+    return month(static_cast<unsigned>(m))/last;
+}
+
+CONSTCD11
+inline
+month_day_last
+operator/(last_spec, int m) NOEXCEPT
+{
+    return m/last;
+}
+
+// month_weekday from operator/()
+
+CONSTCD11
+inline
+month_weekday
+operator/(const month& m, const weekday_indexed& wdi) NOEXCEPT
+{
+    return {m, wdi};
+}
+
+CONSTCD11
+inline
+month_weekday
+operator/(const weekday_indexed& wdi, const month& m) NOEXCEPT
+{
+    return m / wdi;
+}
+
+CONSTCD11
+inline
+month_weekday
+operator/(int m, const weekday_indexed& wdi) NOEXCEPT
+{
+    return month(static_cast<unsigned>(m)) / wdi;
+}
+
+CONSTCD11
+inline
+month_weekday
+operator/(const weekday_indexed& wdi, int m) NOEXCEPT
+{
+    return m / wdi;
+}
+
+// month_weekday_last from operator/()
+
+CONSTCD11
+inline
+month_weekday_last
+operator/(const month& m, const weekday_last& wdl) NOEXCEPT
+{
+    return {m, wdl};
+}
+
+CONSTCD11
+inline
+month_weekday_last
+operator/(const weekday_last& wdl, const month& m) NOEXCEPT
+{
+    return m / wdl;
+}
+
+CONSTCD11
+inline
+month_weekday_last
+operator/(int m, const weekday_last& wdl) NOEXCEPT
+{
+    return month(static_cast<unsigned>(m)) / wdl;
+}
+
+CONSTCD11
+inline
+month_weekday_last
+operator/(const weekday_last& wdl, int m) NOEXCEPT
+{
+    return m / wdl;
+}
+
+// year_month_day from operator/()
+
+CONSTCD11
+inline
+year_month_day
+operator/(const year_month& ym, const day& d) NOEXCEPT
+{
+    return {ym.year(), ym.month(), d};
+}
+
+CONSTCD11
+inline
+year_month_day
+operator/(const year_month& ym, int d)  NOEXCEPT
+{
+    return ym / day(static_cast<unsigned>(d));
+}
+
+CONSTCD11
+inline
+year_month_day
+operator/(const year& y, const month_day& md) NOEXCEPT
+{
+    return y / md.month() / md.day();
+}
+
+CONSTCD11
+inline
+year_month_day
+operator/(int y, const month_day& md) NOEXCEPT
+{
+    return year(y) / md;
+}
+
+CONSTCD11
+inline
+year_month_day
+operator/(const month_day& md, const year& y)  NOEXCEPT
+{
+    return y / md;
+}
+
+CONSTCD11
+inline
+year_month_day
+operator/(const month_day& md, int y) NOEXCEPT
+{
+    return year(y) / md;
+}
+
+// year_month_day_last from operator/()
+
+CONSTCD11
+inline
+year_month_day_last
+operator/(const year_month& ym, last_spec) NOEXCEPT
+{
+    return {ym.year(), month_day_last{ym.month()}};
+}
+
+CONSTCD11
+inline
+year_month_day_last
+operator/(const year& y, const month_day_last& mdl) NOEXCEPT
+{
+    return {y, mdl};
+}
+
+CONSTCD11
+inline
+year_month_day_last
+operator/(int y, const month_day_last& mdl) NOEXCEPT
+{
+    return year(y) / mdl;
+}
+
+CONSTCD11
+inline
+year_month_day_last
+operator/(const month_day_last& mdl, const year& y) NOEXCEPT
+{
+    return y / mdl;
+}
+
+CONSTCD11
+inline
+year_month_day_last
+operator/(const month_day_last& mdl, int y) NOEXCEPT
+{
+    return year(y) / mdl;
+}
+
+// year_month_weekday from operator/()
+
+CONSTCD11
+inline
+year_month_weekday
+operator/(const year_month& ym, const weekday_indexed& wdi) NOEXCEPT
+{
+    return {ym.year(), ym.month(), wdi};
+}
+
+CONSTCD11
+inline
+year_month_weekday
+operator/(const year& y, const month_weekday& mwd) NOEXCEPT
+{
+    return {y, mwd.month(), mwd.weekday_indexed()};
+}
+
+CONSTCD11
+inline
+year_month_weekday
+operator/(int y, const month_weekday& mwd) NOEXCEPT
+{
+    return year(y) / mwd;
+}
+
+CONSTCD11
+inline
+year_month_weekday
+operator/(const month_weekday& mwd, const year& y) NOEXCEPT
+{
+    return y / mwd;
+}
+
+CONSTCD11
+inline
+year_month_weekday
+operator/(const month_weekday& mwd, int y) NOEXCEPT
+{
+    return year(y) / mwd;
+}
+
+// year_month_weekday_last from operator/()
+
+CONSTCD11
+inline
+year_month_weekday_last
+operator/(const year_month& ym, const weekday_last& wdl) NOEXCEPT
+{
+    return {ym.year(), ym.month(), wdl};
+}
+
+CONSTCD11
+inline
+year_month_weekday_last
+operator/(const year& y, const month_weekday_last& mwdl) NOEXCEPT
+{
+    return {y, mwdl.month(), mwdl.weekday_last()};
+}
+
+CONSTCD11
+inline
+year_month_weekday_last
+operator/(int y, const month_weekday_last& mwdl) NOEXCEPT
+{
+    return year(y) / mwdl;
+}
+
+CONSTCD11
+inline
+year_month_weekday_last
+operator/(const month_weekday_last& mwdl, const year& y) NOEXCEPT
+{
+    return y / mwdl;
+}
+
+CONSTCD11
+inline
+year_month_weekday_last
+operator/(const month_weekday_last& mwdl, int y) NOEXCEPT
+{
+    return year(y) / mwdl;
+}
+
+}  // namespace julian
+
+#endif  // JULIAN_H
diff --git a/third_party/date-3.0.1/include/date/ptz.h b/third_party/date-3.0.1/include/date/ptz.h
new file mode 100644
index 00000000..ebd6e04e
--- /dev/null
+++ b/third_party/date-3.0.1/include/date/ptz.h
@@ -0,0 +1,861 @@
+#ifndef PTZ_H
+#define PTZ_H
+
+// The MIT License (MIT)
+//
+// Copyright (c) 2017 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// This header allows Posix-style time zones as specified for TZ here:
+// http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap08.html#tag_08_03
+//
+// Posix::time_zone can be constructed with a posix-style string and then used in
+// a zoned_time like so:
+//
+// zoned_time<system_clock::duration, Posix::time_zone> zt{"EST5EDT,M3.2.0,M11.1.0",
+//                                                         system_clock::now()};
+// or:
+//
+// Posix::time_zone tz{"EST5EDT,M3.2.0,M11.1.0"};
+// zoned_time<system_clock::duration, Posix::time_zone> zt{tz, system_clock::now()};
+//
+// If the rule set is missing (everything starting with ','), then the rule is that the
+// alternate offset is never enabled.
+//
+// Note, Posix-style time zones are not recommended for all of the reasons described here:
+// https://stackoverflow.com/tags/timezone/info
+//
+// They are provided here as a non-trivial custom time zone example, and if you really
+// have to have Posix time zones, you're welcome to use this one.
+
+#include "date/tz.h"
+#include <cctype>
+#include <ostream>
+#include <string>
+
+namespace Posix
+{
+
+namespace detail
+{
+
+#if HAS_STRING_VIEW
+
+using string_t = std::string_view;
+
+#else  // !HAS_STRING_VIEW
+
+using string_t = std::string;
+
+#endif  // !HAS_STRING_VIEW
+
+class rule;
+
+void throw_invalid(const string_t& s, unsigned i, const string_t& message);
+unsigned read_date(const string_t& s, unsigned i, rule& r);
+unsigned read_name(const string_t& s, unsigned i, std::string& name);
+unsigned read_signed_time(const string_t& s, unsigned i, std::chrono::seconds& t);
+unsigned read_unsigned_time(const string_t& s, unsigned i, std::chrono::seconds& t);
+unsigned read_unsigned(const string_t& s, unsigned i,  unsigned limit, unsigned& u,
+                       const string_t& message = string_t{});
+
+class rule
+{
+    enum {off, J, M, N};
+
+    date::month m_;
+    date::weekday wd_;
+    unsigned short n_    : 14;
+    unsigned short mode_ : 2;
+    std::chrono::duration<std::int32_t> time_ = std::chrono::hours{2};
+
+public:
+    rule() : mode_(off) {}
+
+    bool ok() const {return mode_ != off;}
+    date::local_seconds operator()(date::year y) const;
+    std::string to_string() const;
+
+    friend std::ostream& operator<<(std::ostream& os, const rule& r);
+    friend unsigned read_date(const string_t& s, unsigned i, rule& r);
+    friend bool operator==(const rule& x, const rule& y);
+};
+
+inline
+bool
+operator==(const rule& x, const rule& y)
+{
+    if (x.mode_ != y.mode_)
+        return false;
+    switch (x.mode_)
+    {
+    case rule::J:
+    case rule::N:
+        return x.n_ == y.n_;
+    case rule::M:
+        return x.m_ == y.m_ && x.n_ == y.n_ && x.wd_ == y.wd_;
+    default:
+        return true;
+    }
+}
+
+inline
+bool
+operator!=(const rule& x, const rule& y)
+{
+    return !(x == y);
+}
+
+inline
+date::local_seconds
+rule::operator()(date::year y) const
+{
+    using date::local_days;
+    using date::January;
+    using date::days;
+    using date::last;
+    using sec = std::chrono::seconds;
+    date::local_seconds t;
+    switch (mode_)
+    {
+    case J:
+        t = local_days{y/January/0} + days{n_ + (y.is_leap() && n_ > 59)} + sec{time_};
+        break;
+    case M:
+        t = (n_ == 5 ? local_days{y/m_/wd_[last]} : local_days{y/m_/wd_[n_]}) + sec{time_};
+        break;
+    case N:
+        t = local_days{y/January/1} + days{n_} + sec{time_};
+        break;
+    default:
+        assert(!"rule called with bad mode");
+    }
+    return t;
+}
+
+inline
+std::string
+rule::to_string() const
+{
+    using namespace std::chrono;
+    auto print_offset = [](seconds off)
+        {
+            std::string nm;
+            if (off != hours{2})
+            {
+                date::hh_mm_ss<seconds> offset{off};
+                nm = '/';
+                nm += std::to_string(offset.hours().count());
+                if (offset.minutes() != minutes{0} || offset.seconds() != seconds{0})
+                {
+                    nm += ':';
+                    if (offset.minutes() < minutes{10})
+                        nm += '0';
+                    nm += std::to_string(offset.minutes().count());
+                    if (offset.seconds() != seconds{0})
+                    {
+                        nm += ':';
+                        if (offset.seconds() < seconds{10})
+                            nm += '0';
+                        nm += std::to_string(offset.seconds().count());
+                    }
+                }
+            }
+            return nm;
+        };
+
+    std::string nm;
+    switch (mode_)
+    {
+    case rule::J:
+        nm = 'J';
+        nm += std::to_string(n_);
+        break;
+    case rule::M:
+        nm = 'M';
+        nm += std::to_string(static_cast<unsigned>(m_));
+        nm += '.';
+        nm += std::to_string(n_);
+        nm += '.';
+        nm += std::to_string(wd_.c_encoding());
+        break;
+    case rule::N:
+        nm = std::to_string(n_);
+        break;
+    default:
+        break;
+    }
+    nm += print_offset(time_);
+    return nm;
+}
+
+inline
+std::ostream&
+operator<<(std::ostream& os, const rule& r)
+{
+    switch (r.mode_)
+    {
+    case rule::J:
+        os << 'J' << r.n_ << date::format(" %T", r.time_);
+        break;
+    case rule::M:
+        if (r.n_ == 5)
+            os << r.m_/r.wd_[date::last];
+        else
+            os << r.m_/r.wd_[r.n_];
+        os <<  date::format(" %T", r.time_);
+        break;
+    case rule::N:
+        os << r.n_ << date::format(" %T", r.time_);
+        break;
+    default:
+        break;
+    }
+    return os;
+}
+
+}  // namespace detail
+
+class time_zone
+{
+    std::string          std_abbrev_;
+    std::string          dst_abbrev_ = {};
+    std::chrono::seconds offset_;
+    std::chrono::seconds save_ = std::chrono::hours{1};
+    detail::rule         start_rule_;
+    detail::rule         end_rule_;
+
+public:
+    explicit time_zone(const detail::string_t& name);
+
+    template <class Duration>
+        date::sys_info   get_info(date::sys_time<Duration> st) const;
+    template <class Duration>
+        date::local_info get_info(date::local_time<Duration> tp) const;
+
+    template <class Duration>
+        date::sys_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+        to_sys(date::local_time<Duration> tp) const;
+
+    template <class Duration>
+        date::sys_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+        to_sys(date::local_time<Duration> tp, date::choose z) const;
+
+    template <class Duration>
+        date::local_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+        to_local(date::sys_time<Duration> tp) const;
+
+    friend std::ostream& operator<<(std::ostream& os, const time_zone& z);
+
+    const time_zone* operator->() const {return this;}
+
+    std::string name() const;
+
+    friend bool operator==(const time_zone& x, const time_zone& y);
+
+private:
+    date::sys_seconds get_start(date::year y) const;
+    date::sys_seconds get_prev_start(date::year y) const;
+    date::sys_seconds get_next_start(date::year y) const;
+    date::sys_seconds get_end(date::year y) const;
+    date::sys_seconds get_prev_end(date::year y) const;
+    date::sys_seconds get_next_end(date::year y) const;
+    date::sys_info contant_offset() const;
+};
+
+inline
+date::sys_seconds
+time_zone::get_start(date::year y) const
+{
+    return date::sys_seconds{(start_rule_(y) - offset_).time_since_epoch()};
+}
+
+inline
+date::sys_seconds
+time_zone::get_prev_start(date::year y) const
+{
+    return date::sys_seconds{(start_rule_(--y) - offset_).time_since_epoch()};
+}
+
+inline
+date::sys_seconds
+time_zone::get_next_start(date::year y) const
+{
+    return date::sys_seconds{(start_rule_(++y) - offset_).time_since_epoch()};
+}
+
+inline
+date::sys_seconds
+time_zone::get_end(date::year y) const
+{
+    return date::sys_seconds{(end_rule_(y) - (offset_ + save_)).time_since_epoch()};
+}
+
+inline
+date::sys_seconds
+time_zone::get_prev_end(date::year y) const
+{
+    return date::sys_seconds{(end_rule_(--y) - (offset_ + save_)).time_since_epoch()};
+}
+
+inline
+date::sys_seconds
+time_zone::get_next_end(date::year y) const
+{
+    return date::sys_seconds{(end_rule_(++y) - (offset_ + save_)).time_since_epoch()};
+}
+
+date::sys_info
+time_zone::contant_offset() const
+{
+    using date::year;
+    using date::sys_info;
+    using date::sys_days;
+    using date::January;
+    using date::December;
+    using date::last;
+    sys_info r;
+    r.begin = sys_days{year::min()/January/1};
+    r.end   = sys_days{year::max()/December/last};
+    r.abbrev = std_abbrev_;
+    r.offset = offset_;
+    return r;
+}
+
+inline
+time_zone::time_zone(const detail::string_t& s)
+{
+    using detail::read_name;
+    using detail::read_signed_time;
+    using detail::throw_invalid;
+    auto i = read_name(s, 0, std_abbrev_);
+    i = read_signed_time(s, i, offset_);
+    offset_ = -offset_;
+    if (i != s.size())
+    {
+        i = read_name(s, i, dst_abbrev_);
+        if (i != s.size())
+        {
+            if (s[i] != ',')
+            {
+                i = read_signed_time(s, i, save_);
+                save_ = -save_ - offset_;
+            }
+            if (i != s.size())
+            {
+                if (s[i] != ',')
+                    throw_invalid(s, i, "Expecting end of string or ',' to start rule");
+                ++i;
+                i = read_date(s, i, start_rule_);
+                if (i == s.size() || s[i] != ',')
+                    throw_invalid(s, i, "Expecting ',' and then the ending rule");
+                ++i;
+                i = read_date(s, i, end_rule_);
+                if (i != s.size())
+                    throw_invalid(s, i, "Found unexpected trailing characters");
+            }
+        }
+    }
+}
+
+template <class Duration>
+date::sys_info
+time_zone::get_info(date::sys_time<Duration> st) const
+{
+    using date::sys_info;
+    using date::year_month_day;
+    using date::sys_days;
+    using date::floor;
+    using date::ceil;
+    using date::days;
+    using date::year;
+    using date::January;
+    using date::December;
+    using date::last;
+    using std::chrono::minutes;
+    sys_info r{};
+    r.offset = offset_;
+    if (start_rule_.ok())
+    {
+        auto y = year_month_day{floor<days>(st)}.year();
+        auto start = get_start(y);
+        auto end   = get_end(y);
+        if (start <= end)  // (northern hemisphere)
+        {
+            if (start <= st && st < end)
+            {
+                r.begin = start;
+                r.end = end;
+                r.offset += save_;
+                r.save = ceil<minutes>(save_);
+                r.abbrev = dst_abbrev_;
+            }
+            else if (st < start)
+            {
+                r.begin = get_prev_end(y);
+                r.end = start;
+                r.abbrev = std_abbrev_;
+            }
+            else  // st >= end
+            {
+                r.begin = end;
+                r.end = get_next_start(y);
+                r.abbrev = std_abbrev_;
+            }
+        }
+        else  // end < start (southern hemisphere)
+        {
+            if (end <= st && st < start)
+            {
+                r.begin = end;
+                r.end = start;
+                r.abbrev = std_abbrev_;
+            }
+            else if (st < end)
+            {
+                r.begin = get_prev_start(y);
+                r.end = end;
+                r.offset += save_;
+                r.save = ceil<minutes>(save_);
+                r.abbrev = dst_abbrev_;
+            }
+            else  // st >= start
+            {
+                r.begin = start;
+                r.end = get_next_end(y);
+                r.offset += save_;
+                r.save = ceil<minutes>(save_);
+                r.abbrev = dst_abbrev_;
+            }
+        }
+    }
+    else
+        r = contant_offset();
+    return r;
+}
+
+template <class Duration>
+date::local_info
+time_zone::get_info(date::local_time<Duration> tp) const
+{
+    using date::local_info;
+    using date::year_month_day;
+    using date::days;
+    using date::sys_days;
+    using date::sys_seconds;
+    using date::year;
+    using date::ceil;
+    using date::January;
+    using date::December;
+    using date::last;
+    using std::chrono::seconds;
+    using std::chrono::minutes;
+    local_info r{};
+    using date::floor;
+    if (start_rule_.ok())
+    {
+        auto y = year_month_day{floor<days>(tp)}.year();
+        auto start = get_start(y);
+        auto end   = get_end(y);
+        auto utcs = sys_seconds{floor<seconds>(tp - offset_).time_since_epoch()};
+        auto utcd = sys_seconds{floor<seconds>(tp - (offset_ + save_)).time_since_epoch()};
+        auto northern = start <= end;
+        if ((utcs < start) != (utcd < start))
+        {
+            if (northern)
+                r.first.begin = get_prev_end(y);
+            else
+                r.first.begin = end;
+            r.first.end = start;
+            r.first.offset = offset_;
+            r.first.abbrev = std_abbrev_;
+            r.second.begin = start;
+            if (northern)
+                r.second.end = end;
+            else
+                r.second.end = get_next_end(y);
+            r.second.abbrev = dst_abbrev_;
+            r.second.offset = offset_ + save_;
+            r.second.save = ceil<minutes>(save_);
+            r.result = save_ > seconds{0} ? local_info::nonexistent
+                                          : local_info::ambiguous;
+        }
+        else if ((utcs < end) != (utcd < end))
+        {
+            if (northern)
+                r.first.begin = start;
+            else
+                r.first.begin = get_prev_start(y);
+            r.first.end = end;
+            r.first.offset = offset_ + save_;
+            r.first.save = ceil<minutes>(save_);
+            r.first.abbrev = dst_abbrev_;
+            r.second.begin = end;
+            if (northern)
+                r.second.end = get_next_start(y);
+            else
+                r.second.end = start;
+            r.second.abbrev = std_abbrev_;
+            r.second.offset = offset_;
+            r.result = save_ > seconds{0} ? local_info::ambiguous
+                                          : local_info::nonexistent;
+        }
+        else
+            r.first = get_info(utcs);
+    }
+    else
+        r.first = contant_offset();
+    return r;
+}
+
+template <class Duration>
+date::sys_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+time_zone::to_sys(date::local_time<Duration> tp) const
+{
+    using date::local_info;
+    using date::sys_time;
+    using date::ambiguous_local_time;
+    using date::nonexistent_local_time;
+    auto i = get_info(tp);
+    if (i.result == local_info::nonexistent)
+        throw nonexistent_local_time(tp, i);
+    else if (i.result == local_info::ambiguous)
+        throw ambiguous_local_time(tp, i);
+    return sys_time<Duration>{tp.time_since_epoch()} - i.first.offset;
+}
+
+template <class Duration>
+date::sys_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+time_zone::to_sys(date::local_time<Duration> tp, date::choose z) const
+{
+    using date::local_info;
+    using date::sys_time;
+    using date::choose;
+    auto i = get_info(tp);
+    if (i.result == local_info::nonexistent)
+    {
+        return i.first.end;
+    }
+    else if (i.result == local_info::ambiguous)
+    {
+        if (z == choose::latest)
+            return sys_time<Duration>{tp.time_since_epoch()} - i.second.offset;
+    }
+    return sys_time<Duration>{tp.time_since_epoch()} - i.first.offset;
+}
+
+template <class Duration>
+date::local_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+time_zone::to_local(date::sys_time<Duration> tp) const
+{
+    using date::local_time;
+    using std::chrono::seconds;
+    using LT = local_time<typename std::common_type<Duration, seconds>::type>;
+    auto i = get_info(tp);
+    return LT{(tp + i.offset).time_since_epoch()};
+}
+
+inline
+std::ostream&
+operator<<(std::ostream& os, const time_zone& z)
+{
+    using date::operator<<;
+    os << '{';
+    os << z.std_abbrev_ << ", " << z.dst_abbrev_ << date::format(", %T, ", z.offset_)
+       << date::format("%T, [", z.save_) << z.start_rule_ << ", " << z.end_rule_ << ")}";
+    return os;
+}
+
+inline
+std::string
+time_zone::name() const
+{
+    using namespace date;
+    using namespace std::chrono;
+    auto nm = std_abbrev_;
+    auto print_offset = [](seconds off)
+        {
+            std::string nm;
+            hh_mm_ss<seconds> offset{-off};
+            if (offset.is_negative())
+                nm += '-';
+            nm += std::to_string(offset.hours().count());
+            if (offset.minutes() != minutes{0} || offset.seconds() != seconds{0})
+            {
+                nm += ':';
+                if (offset.minutes() < minutes{10})
+                    nm += '0';
+                nm += std::to_string(offset.minutes().count());
+                if (offset.seconds() != seconds{0})
+                {
+                    nm += ':';
+                    if (offset.seconds() < seconds{10})
+                        nm += '0';
+                    nm += std::to_string(offset.seconds().count());
+                }
+            }
+            return nm;
+        };
+    nm += print_offset(offset_);
+    if (!dst_abbrev_.empty())
+    {
+        nm += dst_abbrev_;
+        if (save_ != hours{1})
+            nm += print_offset(offset_+save_);
+        if (start_rule_.ok())
+        {
+            nm += ',';
+            nm += start_rule_.to_string();
+            nm += ',';
+            nm += end_rule_.to_string();
+        }
+    }
+    return nm;
+}
+
+inline
+bool
+operator==(const time_zone& x, const time_zone& y)
+{
+    return x.std_abbrev_ == y.std_abbrev_ &&
+           x.dst_abbrev_ == y. dst_abbrev_ &&
+           x.offset_ == y.offset_ &&
+           x.save_ == y.save_ &&
+           x.start_rule_ == y.start_rule_ &&
+           x.end_rule_ == y.end_rule_;
+}
+
+inline
+bool
+operator!=(const time_zone& x, const time_zone& y)
+{
+    return !(x == y);
+}
+
+namespace detail
+{
+
+inline
+void
+throw_invalid(const string_t& s, unsigned i, const string_t& message)
+{
+    throw std::runtime_error(std::string("Invalid time_zone initializer.\n") +
+                             std::string(message) + ":\n" +
+                             std::string(s) + '\n' +
+                             "\x1b[1;32m" +
+                             std::string(i, '~') + '^' +
+                             std::string(i < s.size() ? s.size()-i-1 : 0, '~') +
+                             "\x1b[0m");
+}
+
+inline
+unsigned
+read_date(const string_t& s, unsigned i, rule& r)
+{
+    using date::month;
+    using date::weekday;
+    if (i == s.size())
+        throw_invalid(s, i, "Expected rule but found end of string");
+    if (s[i] == 'J')
+    {
+        ++i;
+        unsigned n;
+        i = read_unsigned(s, i, 3, n, "Expected to find the Julian day [1, 365]");
+        r.mode_ = rule::J;
+        r.n_ = n;
+    }
+    else if (s[i] == 'M')
+    {
+        ++i;
+        unsigned m;
+        i = read_unsigned(s, i, 2, m, "Expected to find month [1, 12]");
+        if (i == s.size() || s[i] != '.')
+            throw_invalid(s, i, "Expected '.' after month");
+        ++i;
+        unsigned n;
+        i = read_unsigned(s, i, 1, n, "Expected to find week number [1, 5]");
+        if (i == s.size() || s[i] != '.')
+            throw_invalid(s, i, "Expected '.' after weekday index");
+        ++i;
+        unsigned wd;
+        i = read_unsigned(s, i, 1, wd, "Expected to find day of week [0, 6]");
+        r.mode_ = rule::M;
+        r.m_ = month{m};
+        r.wd_ = weekday{wd};
+        r.n_ = n;
+    }
+    else if (std::isdigit(s[i]))
+    {
+        unsigned n;
+        i = read_unsigned(s, i, 3, n);
+        r.mode_ = rule::N;
+        r.n_ = n;
+    }
+    else
+        throw_invalid(s, i, "Expected 'J', 'M', or a digit to start rule");
+    if (i != s.size() && s[i] == '/')
+    {
+        ++i;
+        std::chrono::seconds t;
+        i = read_unsigned_time(s, i, t);
+        r.time_ = t;
+    }
+    return i;
+}
+
+inline
+unsigned
+read_name(const string_t& s, unsigned i, std::string& name)
+{
+    if (i == s.size())
+        throw_invalid(s, i, "Expected a name but found end of string");
+    if (s[i] == '<')
+    {
+        ++i;
+        while (true)
+        {
+            if (i == s.size())
+                throw_invalid(s, i,
+                              "Expected to find closing '>', but found end of string");
+            if (s[i] == '>')
+                break;
+            name.push_back(s[i]);
+            ++i;
+        }
+        ++i;
+    }
+    else
+    {
+        while (i != s.size() && std::isalpha(s[i]))
+        {
+            name.push_back(s[i]);
+            ++i;
+        }
+    }
+    if (name.size() < 3)
+        throw_invalid(s, i, "Found name to be shorter than 3 characters");
+    return i;
+}
+
+inline
+unsigned
+read_signed_time(const string_t& s, unsigned i,
+                                  std::chrono::seconds& t)
+{
+    if (i == s.size())
+        throw_invalid(s, i, "Expected to read signed time, but found end of string");
+    bool negative = false;
+    if (s[i] == '-')
+    {
+        negative = true;
+        ++i;
+    }
+    else if (s[i] == '+')
+        ++i;
+    i = read_unsigned_time(s, i, t);
+    if (negative)
+        t = -t;
+    return i;
+}
+
+inline
+unsigned
+read_unsigned_time(const string_t& s, unsigned i, std::chrono::seconds& t)
+{
+    using std::chrono::seconds;
+    using std::chrono::minutes;
+    using std::chrono::hours;
+    if (i == s.size())
+        throw_invalid(s, i, "Expected to read unsigned time, but found end of string");
+    unsigned x;
+    i = read_unsigned(s, i, 2, x, "Expected to find hours [0, 24]");
+    t = hours{x};
+    if (i != s.size() && s[i] == ':')
+    {
+        ++i;
+        i = read_unsigned(s, i, 2, x, "Expected to find minutes [0, 59]");
+        t += minutes{x};
+        if (i != s.size() && s[i] == ':')
+        {
+            ++i;
+            i = read_unsigned(s, i, 2, x, "Expected to find seconds [0, 59]");
+            t += seconds{x};
+        }
+    }
+    return i;
+}
+
+inline
+unsigned
+read_unsigned(const string_t& s, unsigned i, unsigned limit, unsigned& u,
+              const string_t& message)
+{
+    if (i == s.size() || !std::isdigit(s[i]))
+        throw_invalid(s, i, message);
+    u = static_cast<unsigned>(s[i] - '0');
+    unsigned count = 1;
+    for (++i; count < limit && i != s.size() && std::isdigit(s[i]); ++i, ++count)
+        u = u * 10 + static_cast<unsigned>(s[i] - '0');
+    return i;
+}
+
+}  // namespace detail
+
+}  // namespace Posix
+
+namespace date
+{
+
+template <>
+struct zoned_traits<Posix::time_zone>
+{
+
+#if HAS_STRING_VIEW
+
+    static
+    Posix::time_zone
+    locate_zone(std::string_view name)
+    {
+        return Posix::time_zone{name};
+    }
+
+#else  // !HAS_STRING_VIEW
+
+    static
+    Posix::time_zone
+    locate_zone(const std::string& name)
+    {
+        return Posix::time_zone{name};
+    }
+
+    static
+    Posix::time_zone
+    locate_zone(const char* name)
+    {
+        return Posix::time_zone{name};
+    }
+
+#endif  // !HAS_STRING_VIEW
+
+};
+
+}  // namespace date
+
+#endif  // PTZ_H
diff --git a/third_party/date-3.0.1/include/date/solar_hijri.h b/third_party/date-3.0.1/include/date/solar_hijri.h
new file mode 100644
index 00000000..6f6c331b
--- /dev/null
+++ b/third_party/date-3.0.1/include/date/solar_hijri.h
@@ -0,0 +1,3151 @@
+#ifndef SOLAR_HIJRI_H
+#define SOLAR_HIJRI_H
+
+// The MIT License (MIT)
+//
+// Copyright (c) 2016 Howard Hinnant
+// Copyright (c) 2019 Asad. Gharighi
+//
+// Calculations are based on:
+// https://www.timeanddate.com/calendar/persian-calendar.html
+// and follow <date.h> style
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+//
+// Our apologies.  When the previous paragraph was written, lowercase had not yet
+// been invented (that would involve another several millennia of evolution).
+// We did not mean to shout.
+
+#include "date.h"
+
+namespace solar_hijri
+{
+
+namespace internal
+{
+static const auto epoch = static_cast<unsigned>(2121446);
+static const auto days_in_era = static_cast<unsigned>(1029983);
+static const auto years_in_era = static_cast<unsigned>(2820);
+static const auto unix_time_shift = static_cast<unsigned>(2440588);
+auto const years_in_first_cycle = static_cast<unsigned>(29);
+auto const years_in_other_cycles = static_cast<int>(33);
+auto const years_in_period = static_cast<int>(128);        // 29   + 3*33
+auto const days_in_first_cycle = static_cast<unsigned>(10592);  // 28/4 + 29*365
+auto const days_in_other_cycles = static_cast<unsigned>(12053); // 32/4 + 33*365
+auto const days_in_period = static_cast<unsigned>(46751);       // days_in_first_cycle + 3*days_in_other_cycles;
+}
+
+// durations
+
+using days = date::days;
+
+using weeks = date::weeks;
+
+using years = std::chrono::duration
+              <int, date::detail::ratio_multiply<std::ratio<internal::days_in_era, internal::years_in_era>, days::period>>;
+
+using months = std::chrono::duration
+    <int, date::detail::ratio_divide<years::period, std::ratio<12>>>;
+
+// time_point
+
+using sys_days   = date::sys_days;
+using local_days = date::local_days;
+
+// types
+
+struct last_spec
+{
+    explicit last_spec() = default;
+};
+
+class day;
+class month;
+class year;
+
+class weekday;
+class weekday_indexed;
+class weekday_last;
+
+class month_day;
+class month_day_last;
+class month_weekday;
+class month_weekday_last;
+
+class year_month;
+
+class year_month_day;
+class year_month_day_last;
+class year_month_weekday;
+class year_month_weekday_last;
+
+// date composition operators
+
+CONSTCD11 year_month operator/(const year& y, const month& m) NOEXCEPT;
+CONSTCD11 year_month operator/(const year& y, int          m) NOEXCEPT;
+
+CONSTCD11 month_day operator/(const day& d, const month& m) NOEXCEPT;
+CONSTCD11 month_day operator/(const day& d, int          m) NOEXCEPT;
+CONSTCD11 month_day operator/(const month& m, const day& d) NOEXCEPT;
+CONSTCD11 month_day operator/(const month& m, int        d) NOEXCEPT;
+CONSTCD11 month_day operator/(int          m, const day& d) NOEXCEPT;
+
+CONSTCD11 month_day_last operator/(const month& m, last_spec) NOEXCEPT;
+CONSTCD11 month_day_last operator/(int          m, last_spec) NOEXCEPT;
+CONSTCD11 month_day_last operator/(last_spec, const month& m) NOEXCEPT;
+CONSTCD11 month_day_last operator/(last_spec, int          m) NOEXCEPT;
+
+CONSTCD11 month_weekday operator/(const month& m, const weekday_indexed& wdi) NOEXCEPT;
+CONSTCD11 month_weekday operator/(int          m, const weekday_indexed& wdi) NOEXCEPT;
+CONSTCD11 month_weekday operator/(const weekday_indexed& wdi, const month& m) NOEXCEPT;
+CONSTCD11 month_weekday operator/(const weekday_indexed& wdi, int          m) NOEXCEPT;
+
+CONSTCD11 month_weekday_last operator/(const month& m, const weekday_last& wdl) NOEXCEPT;
+CONSTCD11 month_weekday_last operator/(int          m, const weekday_last& wdl) NOEXCEPT;
+CONSTCD11 month_weekday_last operator/(const weekday_last& wdl, const month& m) NOEXCEPT;
+CONSTCD11 month_weekday_last operator/(const weekday_last& wdl, int          m) NOEXCEPT;
+
+CONSTCD11 year_month_day operator/(const year_month& ym, const day& d) NOEXCEPT;
+CONSTCD11 year_month_day operator/(const year_month& ym, int        d) NOEXCEPT;
+CONSTCD11 year_month_day operator/(const year& y, const month_day& md) NOEXCEPT;
+CONSTCD11 year_month_day operator/(int         y, const month_day& md) NOEXCEPT;
+CONSTCD11 year_month_day operator/(const month_day& md, const year& y) NOEXCEPT;
+CONSTCD11 year_month_day operator/(const month_day& md, int         y) NOEXCEPT;
+
+CONSTCD11
+    year_month_day_last operator/(const year_month& ym,   last_spec) NOEXCEPT;
+CONSTCD11
+    year_month_day_last operator/(const year& y, const month_day_last& mdl) NOEXCEPT;
+CONSTCD11
+    year_month_day_last operator/(int         y, const month_day_last& mdl) NOEXCEPT;
+CONSTCD11
+    year_month_day_last operator/(const month_day_last& mdl, const year& y) NOEXCEPT;
+CONSTCD11
+    year_month_day_last operator/(const month_day_last& mdl, int         y) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday
+operator/(const year_month& ym, const weekday_indexed& wdi) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday
+operator/(const year&        y, const month_weekday&   mwd) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday
+operator/(int                y, const month_weekday&   mwd) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday
+operator/(const month_weekday& mwd, const year&          y) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday
+operator/(const month_weekday& mwd, int                  y) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday_last
+operator/(const year_month& ym, const weekday_last& wdl) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday_last
+operator/(const year& y, const month_weekday_last& mwdl) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday_last
+operator/(int         y, const month_weekday_last& mwdl) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday_last
+operator/(const month_weekday_last& mwdl, const year& y) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday_last
+operator/(const month_weekday_last& mwdl, int         y) NOEXCEPT;
+
+// Detailed interface
+
+// day
+
+class day
+{
+    unsigned char d_;
+
+public:
+    day() = default;
+    explicit CONSTCD11 day(unsigned d) NOEXCEPT;
+
+    CONSTCD14 day& operator++()    NOEXCEPT;
+    CONSTCD14 day  operator++(int) NOEXCEPT;
+    CONSTCD14 day& operator--()    NOEXCEPT;
+    CONSTCD14 day  operator--(int) NOEXCEPT;
+
+    CONSTCD14 day& operator+=(const days& d) NOEXCEPT;
+    CONSTCD14 day& operator-=(const days& d) NOEXCEPT;
+
+    CONSTCD11 explicit operator unsigned() const NOEXCEPT;
+    CONSTCD11 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const day& x, const day& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const day& x, const day& y) NOEXCEPT;
+CONSTCD11 bool operator< (const day& x, const day& y) NOEXCEPT;
+CONSTCD11 bool operator> (const day& x, const day& y) NOEXCEPT;
+CONSTCD11 bool operator<=(const day& x, const day& y) NOEXCEPT;
+CONSTCD11 bool operator>=(const day& x, const day& y) NOEXCEPT;
+
+CONSTCD11 day  operator+(const day&  x, const days& y) NOEXCEPT;
+CONSTCD11 day  operator+(const days& x, const day&  y) NOEXCEPT;
+CONSTCD11 day  operator-(const day&  x, const days& y) NOEXCEPT;
+CONSTCD11 days operator-(const day&  x, const day&  y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const day& d);
+
+// month
+
+class month
+{
+    unsigned char m_;
+
+public:
+    month() = default;
+    explicit CONSTCD11 month(unsigned m) NOEXCEPT;
+
+    CONSTCD14 month& operator++()    NOEXCEPT;
+    CONSTCD14 month  operator++(int) NOEXCEPT;
+    CONSTCD14 month& operator--()    NOEXCEPT;
+    CONSTCD14 month  operator--(int) NOEXCEPT;
+
+    CONSTCD14 month& operator+=(const months& m) NOEXCEPT;
+    CONSTCD14 month& operator-=(const months& m) NOEXCEPT;
+
+    CONSTCD11 explicit operator unsigned() const NOEXCEPT;
+    CONSTCD11 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const month& x, const month& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const month& x, const month& y) NOEXCEPT;
+CONSTCD11 bool operator< (const month& x, const month& y) NOEXCEPT;
+CONSTCD11 bool operator> (const month& x, const month& y) NOEXCEPT;
+CONSTCD11 bool operator<=(const month& x, const month& y) NOEXCEPT;
+CONSTCD11 bool operator>=(const month& x, const month& y) NOEXCEPT;
+
+CONSTCD14 month  operator+(const month&  x, const months& y) NOEXCEPT;
+CONSTCD14 month  operator+(const months& x,  const month& y) NOEXCEPT;
+CONSTCD14 month  operator-(const month&  x, const months& y) NOEXCEPT;
+CONSTCD14 months operator-(const month&  x,  const month& y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const month& m);
+
+// year
+
+class year
+{
+    short y_;
+
+public:
+    year() = default;
+    explicit CONSTCD11 year(int y) NOEXCEPT;
+
+    CONSTCD14 year& operator++()    NOEXCEPT;
+    CONSTCD14 year  operator++(int) NOEXCEPT;
+    CONSTCD14 year& operator--()    NOEXCEPT;
+    CONSTCD14 year  operator--(int) NOEXCEPT;
+
+    CONSTCD14 year& operator+=(const years& y) NOEXCEPT;
+    CONSTCD14 year& operator-=(const years& y) NOEXCEPT;
+
+    CONSTCD14 bool is_leap() const NOEXCEPT;
+
+    CONSTCD11 explicit operator int() const NOEXCEPT;
+    CONSTCD11 bool ok() const NOEXCEPT;
+
+    static CONSTCD11 year min() NOEXCEPT;
+    static CONSTCD11 year max() NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const year& x, const year& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const year& x, const year& y) NOEXCEPT;
+CONSTCD11 bool operator< (const year& x, const year& y) NOEXCEPT;
+CONSTCD11 bool operator> (const year& x, const year& y) NOEXCEPT;
+CONSTCD11 bool operator<=(const year& x, const year& y) NOEXCEPT;
+CONSTCD11 bool operator>=(const year& x, const year& y) NOEXCEPT;
+
+CONSTCD11 year  operator+(const year&  x, const years& y) NOEXCEPT;
+CONSTCD11 year  operator+(const years& x, const year&  y) NOEXCEPT;
+CONSTCD11 year  operator-(const year&  x, const years& y) NOEXCEPT;
+CONSTCD11 years operator-(const year&  x, const year&  y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year& y);
+
+// weekday
+
+class weekday
+{
+    unsigned char wd_;
+public:
+    weekday() = default;
+    explicit CONSTCD11 weekday(unsigned wd) NOEXCEPT;
+    explicit weekday(int) = delete;
+    CONSTCD11 weekday(const sys_days& dp) NOEXCEPT;
+    CONSTCD11 explicit weekday(const local_days& dp) NOEXCEPT;
+
+    CONSTCD14 weekday& operator++()    NOEXCEPT;
+    CONSTCD14 weekday  operator++(int) NOEXCEPT;
+    CONSTCD14 weekday& operator--()    NOEXCEPT;
+    CONSTCD14 weekday  operator--(int) NOEXCEPT;
+
+    CONSTCD14 weekday& operator+=(const days& d) NOEXCEPT;
+    CONSTCD14 weekday& operator-=(const days& d) NOEXCEPT;
+
+    CONSTCD11 explicit operator unsigned() const NOEXCEPT;
+    CONSTCD11 bool ok() const NOEXCEPT;
+
+    CONSTCD11 weekday_indexed operator[](unsigned index) const NOEXCEPT;
+    CONSTCD11 weekday_last    operator[](last_spec)      const NOEXCEPT;
+
+private:
+    static CONSTCD11 unsigned char weekday_from_days(int z) NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const weekday& x, const weekday& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const weekday& x, const weekday& y) NOEXCEPT;
+
+CONSTCD14 weekday operator+(const weekday& x, const days&    y) NOEXCEPT;
+CONSTCD14 weekday operator+(const days&    x, const weekday& y) NOEXCEPT;
+CONSTCD14 weekday operator-(const weekday& x, const days&    y) NOEXCEPT;
+CONSTCD14 days    operator-(const weekday& x, const weekday& y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const weekday& wd);
+
+// weekday_indexed
+
+class weekday_indexed
+{
+    unsigned char wd_    : 4;
+    unsigned char index_ : 4;
+
+public:
+    weekday_indexed() = default;
+    CONSTCD11 weekday_indexed(const solar_hijri::weekday& wd, unsigned index) NOEXCEPT;
+
+    CONSTCD11 solar_hijri::weekday weekday() const NOEXCEPT;
+    CONSTCD11 unsigned index() const NOEXCEPT;
+    CONSTCD11 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const weekday_indexed& x, const weekday_indexed& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const weekday_indexed& x, const weekday_indexed& y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const weekday_indexed& wdi);
+
+// weekday_last
+
+class weekday_last
+{
+    solar_hijri::weekday wd_;
+
+public:
+    weekday_last() = default;
+    explicit CONSTCD11 weekday_last(const solar_hijri::weekday& wd) NOEXCEPT;
+
+    CONSTCD11 solar_hijri::weekday weekday() const NOEXCEPT;
+    CONSTCD11 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const weekday_last& x, const weekday_last& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const weekday_last& x, const weekday_last& y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const weekday_last& wdl);
+
+// year_month
+
+class year_month
+{
+    solar_hijri::year  y_;
+    solar_hijri::month m_;
+
+public:
+    year_month() = default;
+    CONSTCD11 year_month(const solar_hijri::year& y, const solar_hijri::month& m) NOEXCEPT;
+
+    CONSTCD11 solar_hijri::year  year()  const NOEXCEPT;
+    CONSTCD11 solar_hijri::month month() const NOEXCEPT;
+
+    CONSTCD14 year_month& operator+=(const months& dm) NOEXCEPT;
+    CONSTCD14 year_month& operator-=(const months& dm) NOEXCEPT;
+    CONSTCD14 year_month& operator+=(const years& dy) NOEXCEPT;
+    CONSTCD14 year_month& operator-=(const years& dy) NOEXCEPT;
+
+    CONSTCD11 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const year_month& x, const year_month& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const year_month& x, const year_month& y) NOEXCEPT;
+CONSTCD11 bool operator< (const year_month& x, const year_month& y) NOEXCEPT;
+CONSTCD11 bool operator> (const year_month& x, const year_month& y) NOEXCEPT;
+CONSTCD11 bool operator<=(const year_month& x, const year_month& y) NOEXCEPT;
+CONSTCD11 bool operator>=(const year_month& x, const year_month& y) NOEXCEPT;
+
+CONSTCD14 year_month operator+(const year_month& ym, const months& dm) NOEXCEPT;
+CONSTCD14 year_month operator+(const months& dm, const year_month& ym) NOEXCEPT;
+CONSTCD14 year_month operator-(const year_month& ym, const months& dm) NOEXCEPT;
+
+CONSTCD11 months operator-(const year_month& x, const year_month& y) NOEXCEPT;
+CONSTCD11 year_month operator+(const year_month& ym, const years& dy) NOEXCEPT;
+CONSTCD11 year_month operator+(const years& dy, const year_month& ym) NOEXCEPT;
+CONSTCD11 year_month operator-(const year_month& ym, const years& dy) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_month& ym);
+
+// month_day
+
+class month_day
+{
+    solar_hijri::month m_;
+    solar_hijri::day   d_;
+
+public:
+    month_day() = default;
+    CONSTCD11 month_day(const solar_hijri::month& m, const solar_hijri::day& d) NOEXCEPT;
+
+    CONSTCD11 solar_hijri::month month() const NOEXCEPT;
+    CONSTCD11 solar_hijri::day   day() const NOEXCEPT;
+
+    CONSTCD14 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const month_day& x, const month_day& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const month_day& x, const month_day& y) NOEXCEPT;
+CONSTCD11 bool operator< (const month_day& x, const month_day& y) NOEXCEPT;
+CONSTCD11 bool operator> (const month_day& x, const month_day& y) NOEXCEPT;
+CONSTCD11 bool operator<=(const month_day& x, const month_day& y) NOEXCEPT;
+CONSTCD11 bool operator>=(const month_day& x, const month_day& y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const month_day& md);
+
+// month_day_last
+
+class month_day_last
+{
+    solar_hijri::month m_;
+
+public:
+    month_day_last() = default;
+    CONSTCD11 explicit month_day_last(const solar_hijri::month& m) NOEXCEPT;
+
+    CONSTCD11 solar_hijri::month month() const NOEXCEPT;
+    CONSTCD11 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const month_day_last& x, const month_day_last& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const month_day_last& x, const month_day_last& y) NOEXCEPT;
+CONSTCD11 bool operator< (const month_day_last& x, const month_day_last& y) NOEXCEPT;
+CONSTCD11 bool operator> (const month_day_last& x, const month_day_last& y) NOEXCEPT;
+CONSTCD11 bool operator<=(const month_day_last& x, const month_day_last& y) NOEXCEPT;
+CONSTCD11 bool operator>=(const month_day_last& x, const month_day_last& y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const month_day_last& mdl);
+
+// month_weekday
+
+class month_weekday
+{
+    solar_hijri::month           m_;
+    solar_hijri::weekday_indexed wdi_;
+public:
+    month_weekday() = default;
+    CONSTCD11 month_weekday(const solar_hijri::month& m,
+                            const solar_hijri::weekday_indexed& wdi) NOEXCEPT;
+
+    CONSTCD11 solar_hijri::month           month()           const NOEXCEPT;
+    CONSTCD11 solar_hijri::weekday_indexed weekday_indexed() const NOEXCEPT;
+
+    CONSTCD11 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const month_weekday& x, const month_weekday& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const month_weekday& x, const month_weekday& y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const month_weekday& mwd);
+
+// month_weekday_last
+
+class month_weekday_last
+{
+    solar_hijri::month        m_;
+    solar_hijri::weekday_last wdl_;
+
+public:
+    month_weekday_last() = default;
+    CONSTCD11 month_weekday_last(const solar_hijri::month& m,
+                                 const solar_hijri::weekday_last& wd) NOEXCEPT;
+
+    CONSTCD11 solar_hijri::month        month()        const NOEXCEPT;
+    CONSTCD11 solar_hijri::weekday_last weekday_last() const NOEXCEPT;
+
+    CONSTCD11 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11
+    bool operator==(const month_weekday_last& x, const month_weekday_last& y) NOEXCEPT;
+CONSTCD11
+    bool operator!=(const month_weekday_last& x, const month_weekday_last& y) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const month_weekday_last& mwdl);
+
+// class year_month_day
+
+class year_month_day
+{
+    solar_hijri::year  y_;
+    solar_hijri::month m_;
+    solar_hijri::day   d_;
+
+public:
+    year_month_day() = default;
+    CONSTCD11 year_month_day(const solar_hijri::year& y, const solar_hijri::month& m,
+                             const solar_hijri::day& d) NOEXCEPT;
+    CONSTCD14 year_month_day(const year_month_day_last& ymdl) NOEXCEPT;
+
+    CONSTCD14 year_month_day(sys_days dp) NOEXCEPT;
+    CONSTCD14 explicit year_month_day(local_days dp) NOEXCEPT;
+
+    CONSTCD14 year_month_day& operator+=(const months& m) NOEXCEPT;
+    CONSTCD14 year_month_day& operator-=(const months& m) NOEXCEPT;
+    CONSTCD14 year_month_day& operator+=(const years& y)  NOEXCEPT;
+    CONSTCD14 year_month_day& operator-=(const years& y)  NOEXCEPT;
+
+    CONSTCD11 solar_hijri::year  year()  const NOEXCEPT;
+    CONSTCD11 solar_hijri::month month() const NOEXCEPT;
+    CONSTCD11 solar_hijri::day   day()   const NOEXCEPT;
+
+    CONSTCD14 operator sys_days() const NOEXCEPT;
+    CONSTCD14 explicit operator local_days() const NOEXCEPT;
+    CONSTCD14 bool ok() const NOEXCEPT;
+
+private:
+  static CONSTCD14 year_month_day from_days(days dp) NOEXCEPT;
+  CONSTCD14 days to_days() const NOEXCEPT;
+};
+
+CONSTCD11 bool operator==(const year_month_day& x, const year_month_day& y) NOEXCEPT;
+CONSTCD11 bool operator!=(const year_month_day& x, const year_month_day& y) NOEXCEPT;
+CONSTCD11 bool operator< (const year_month_day& x, const year_month_day& y) NOEXCEPT;
+CONSTCD11 bool operator> (const year_month_day& x, const year_month_day& y) NOEXCEPT;
+CONSTCD11 bool operator<=(const year_month_day& x, const year_month_day& y) NOEXCEPT;
+CONSTCD11 bool operator>=(const year_month_day& x, const year_month_day& y) NOEXCEPT;
+
+CONSTCD14 year_month_day operator+(const year_month_day& ymd, const months& dm) NOEXCEPT;
+CONSTCD14 year_month_day operator+(const months& dm, const year_month_day& ymd) NOEXCEPT;
+CONSTCD14 year_month_day operator-(const year_month_day& ymd, const months& dm) NOEXCEPT;
+CONSTCD11 year_month_day operator+(const year_month_day& ymd, const years& dy)  NOEXCEPT;
+CONSTCD11 year_month_day operator+(const years& dy, const year_month_day& ymd)  NOEXCEPT;
+CONSTCD11 year_month_day operator-(const year_month_day& ymd, const years& dy)  NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_month_day& ymd);
+
+// year_month_day_last
+
+class year_month_day_last
+{
+    solar_hijri::year           y_;
+    solar_hijri::month_day_last mdl_;
+
+public:
+    year_month_day_last() = default;
+    CONSTCD11 year_month_day_last(const solar_hijri::year& y,
+                                  const solar_hijri::month_day_last& mdl) NOEXCEPT;
+
+    CONSTCD14 year_month_day_last& operator+=(const months& m) NOEXCEPT;
+    CONSTCD14 year_month_day_last& operator-=(const months& m) NOEXCEPT;
+    CONSTCD14 year_month_day_last& operator+=(const years& y)  NOEXCEPT;
+    CONSTCD14 year_month_day_last& operator-=(const years& y)  NOEXCEPT;
+
+    CONSTCD11 solar_hijri::year           year()           const NOEXCEPT;
+    CONSTCD11 solar_hijri::month          month()          const NOEXCEPT;
+    CONSTCD11 solar_hijri::month_day_last month_day_last() const NOEXCEPT;
+    CONSTCD14 solar_hijri::day            day()            const NOEXCEPT;
+
+    CONSTCD14 operator sys_days() const NOEXCEPT;
+    CONSTCD14 explicit operator local_days() const NOEXCEPT;
+    CONSTCD11 bool ok() const NOEXCEPT;
+};
+
+CONSTCD11
+    bool operator==(const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT;
+CONSTCD11
+    bool operator!=(const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT;
+CONSTCD11
+    bool operator< (const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT;
+CONSTCD11
+    bool operator> (const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT;
+CONSTCD11
+    bool operator<=(const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT;
+CONSTCD11
+    bool operator>=(const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT;
+
+CONSTCD14
+year_month_day_last
+operator+(const year_month_day_last& ymdl, const months& dm) NOEXCEPT;
+
+CONSTCD14
+year_month_day_last
+operator+(const months& dm, const year_month_day_last& ymdl) NOEXCEPT;
+
+CONSTCD11
+year_month_day_last
+operator+(const year_month_day_last& ymdl, const years& dy) NOEXCEPT;
+
+CONSTCD11
+year_month_day_last
+operator+(const years& dy, const year_month_day_last& ymdl) NOEXCEPT;
+
+CONSTCD14
+year_month_day_last
+operator-(const year_month_day_last& ymdl, const months& dm) NOEXCEPT;
+
+CONSTCD11
+year_month_day_last
+operator-(const year_month_day_last& ymdl, const years& dy) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_month_day_last& ymdl);
+
+// year_month_weekday
+
+class year_month_weekday
+{
+    solar_hijri::year            y_;
+    solar_hijri::month           m_;
+    solar_hijri::weekday_indexed wdi_;
+
+public:
+    year_month_weekday() = default;
+    CONSTCD11 year_month_weekday(const solar_hijri::year& y, const solar_hijri::month& m,
+                                   const solar_hijri::weekday_indexed& wdi) NOEXCEPT;
+    CONSTCD14 year_month_weekday(const sys_days& dp) NOEXCEPT;
+    CONSTCD14 explicit year_month_weekday(const local_days& dp) NOEXCEPT;
+
+    CONSTCD14 year_month_weekday& operator+=(const months& m) NOEXCEPT;
+    CONSTCD14 year_month_weekday& operator-=(const months& m) NOEXCEPT;
+    CONSTCD14 year_month_weekday& operator+=(const years& y)  NOEXCEPT;
+    CONSTCD14 year_month_weekday& operator-=(const years& y)  NOEXCEPT;
+
+    CONSTCD11 solar_hijri::year year() const NOEXCEPT;
+    CONSTCD11 solar_hijri::month month() const NOEXCEPT;
+    CONSTCD11 solar_hijri::weekday weekday() const NOEXCEPT;
+    CONSTCD11 unsigned index() const NOEXCEPT;
+    CONSTCD11 solar_hijri::weekday_indexed weekday_indexed() const NOEXCEPT;
+
+    CONSTCD14 operator sys_days() const NOEXCEPT;
+    CONSTCD14 explicit operator local_days() const NOEXCEPT;
+    CONSTCD14 bool ok() const NOEXCEPT;
+
+private:
+    static CONSTCD14 year_month_weekday from_days(days dp) NOEXCEPT;
+    CONSTCD14 days to_days() const NOEXCEPT;
+};
+
+CONSTCD11
+    bool operator==(const year_month_weekday& x, const year_month_weekday& y) NOEXCEPT;
+CONSTCD11
+    bool operator!=(const year_month_weekday& x, const year_month_weekday& y) NOEXCEPT;
+
+CONSTCD14
+year_month_weekday
+operator+(const year_month_weekday& ymwd, const months& dm) NOEXCEPT;
+
+CONSTCD14
+year_month_weekday
+operator+(const months& dm, const year_month_weekday& ymwd) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday
+operator+(const year_month_weekday& ymwd, const years& dy) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday
+operator+(const years& dy, const year_month_weekday& ymwd) NOEXCEPT;
+
+CONSTCD14
+year_month_weekday
+operator-(const year_month_weekday& ymwd, const months& dm) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday
+operator-(const year_month_weekday& ymwd, const years& dy) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_month_weekday& ymwdi);
+
+// year_month_weekday_last
+
+class year_month_weekday_last
+{
+    solar_hijri::year y_;
+    solar_hijri::month m_;
+    solar_hijri::weekday_last wdl_;
+
+public:
+    year_month_weekday_last() = default;
+    CONSTCD11 year_month_weekday_last(const solar_hijri::year& y, const solar_hijri::month& m,
+                                      const solar_hijri::weekday_last& wdl) NOEXCEPT;
+
+    CONSTCD14 year_month_weekday_last& operator+=(const months& m) NOEXCEPT;
+    CONSTCD14 year_month_weekday_last& operator-=(const months& m) NOEXCEPT;
+    CONSTCD14 year_month_weekday_last& operator+=(const years& y) NOEXCEPT;
+    CONSTCD14 year_month_weekday_last& operator-=(const years& y) NOEXCEPT;
+
+    CONSTCD11 solar_hijri::year year() const NOEXCEPT;
+    CONSTCD11 solar_hijri::month month() const NOEXCEPT;
+    CONSTCD11 solar_hijri::weekday weekday() const NOEXCEPT;
+    CONSTCD11 solar_hijri::weekday_last weekday_last() const NOEXCEPT;
+
+    CONSTCD14 operator sys_days() const NOEXCEPT;
+    CONSTCD14 explicit operator local_days() const NOEXCEPT;
+    CONSTCD11 bool ok() const NOEXCEPT;
+
+private:
+    CONSTCD14 days to_days() const NOEXCEPT;
+};
+
+CONSTCD11
+bool
+operator==(const year_month_weekday_last& x, const year_month_weekday_last& y) NOEXCEPT;
+
+CONSTCD11
+bool
+operator!=(const year_month_weekday_last& x, const year_month_weekday_last& y) NOEXCEPT;
+
+CONSTCD14
+year_month_weekday_last
+operator+(const year_month_weekday_last& ymwdl, const months& dm) NOEXCEPT;
+
+CONSTCD14
+year_month_weekday_last
+operator+(const months& dm, const year_month_weekday_last& ymwdl) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday_last
+operator+(const year_month_weekday_last& ymwdl, const years& dy) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday_last
+operator+(const years& dy, const year_month_weekday_last& ymwdl) NOEXCEPT;
+
+CONSTCD14
+year_month_weekday_last
+operator-(const year_month_weekday_last& ymwdl, const months& dm) NOEXCEPT;
+
+CONSTCD11
+year_month_weekday_last
+operator-(const year_month_weekday_last& ymwdl, const years& dy) NOEXCEPT;
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_month_weekday_last& ymwdl);
+
+#if !defined(_MSC_VER) || (_MSC_VER >= 1900)
+inline namespace literals
+{
+
+CONSTCD11 solar_hijri::day  operator "" _d(unsigned long long d) NOEXCEPT;
+CONSTCD11 solar_hijri::year operator "" _y(unsigned long long y) NOEXCEPT;
+
+}  // inline namespace literals
+#endif // !defined(_MSC_VER) || (_MSC_VER >= 1900)
+
+//----------------+
+// Implementation |
+//----------------+
+
+// day
+
+CONSTCD11 inline day::day(unsigned d) NOEXCEPT : d_(static_cast<unsigned char>(d)) {}
+CONSTCD14 inline day& day::operator++() NOEXCEPT {++d_; return *this;}
+CONSTCD14 inline day day::operator++(int) NOEXCEPT {auto tmp(*this); ++(*this); return tmp;}
+CONSTCD14 inline day& day::operator--() NOEXCEPT {--d_; return *this;}
+CONSTCD14 inline day day::operator--(int) NOEXCEPT {auto tmp(*this); --(*this); return tmp;}
+CONSTCD14 inline day& day::operator+=(const days& d) NOEXCEPT {*this = *this + d; return *this;}
+CONSTCD14 inline day& day::operator-=(const days& d) NOEXCEPT {*this = *this - d; return *this;}
+CONSTCD11 inline day::operator unsigned() const NOEXCEPT {return d_;}
+CONSTCD11 inline bool day::ok() const NOEXCEPT {return 1 <= d_ && d_ <= 30;}
+
+CONSTCD11
+inline
+bool
+operator==(const day& x, const day& y) NOEXCEPT
+{
+    return static_cast<unsigned>(x) == static_cast<unsigned>(y);
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const day& x, const day& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+CONSTCD11
+inline
+bool
+operator<(const day& x, const day& y) NOEXCEPT
+{
+    return static_cast<unsigned>(x) < static_cast<unsigned>(y);
+}
+
+CONSTCD11
+inline
+bool
+operator>(const day& x, const day& y) NOEXCEPT
+{
+    return y < x;
+}
+
+CONSTCD11
+inline
+bool
+operator<=(const day& x, const day& y) NOEXCEPT
+{
+    return !(y < x);
+}
+
+CONSTCD11
+inline
+bool
+operator>=(const day& x, const day& y) NOEXCEPT
+{
+    return !(x < y);
+}
+
+CONSTCD11
+inline
+days
+operator-(const day& x, const day& y) NOEXCEPT
+{
+    return days{static_cast<days::rep>(static_cast<unsigned>(x)
+                                     - static_cast<unsigned>(y))};
+}
+
+CONSTCD11
+inline
+day
+operator+(const day& x, const days& y) NOEXCEPT
+{
+    return day{static_cast<unsigned>(x) + static_cast<unsigned>(y.count())};
+}
+
+CONSTCD11
+inline
+day
+operator+(const days& x, const day& y) NOEXCEPT
+{
+    return y + x;
+}
+
+CONSTCD11
+inline
+day
+operator-(const day& x, const days& y) NOEXCEPT
+{
+    return x + -y;
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const day& d)
+{
+    date::detail::save_ostream<CharT, Traits> _(os);
+    os.fill('0');
+    os.flags(std::ios::dec | std::ios::right);
+    os.width(2);
+    os << static_cast<unsigned>(d);
+    return os;
+}
+
+// month
+
+CONSTCD11 inline month::month(unsigned m) NOEXCEPT : m_(static_cast<decltype(m_)>(m)) {}
+CONSTCD14 inline month& month::operator++() NOEXCEPT {if (++m_ == 13) m_ = 1; return *this;}
+CONSTCD14 inline month month::operator++(int) NOEXCEPT {auto tmp(*this); ++(*this); return tmp;}
+CONSTCD14 inline month& month::operator--() NOEXCEPT {if (--m_ == 0) m_ = 12; return *this;}
+CONSTCD14 inline month month::operator--(int) NOEXCEPT {auto tmp(*this); --(*this); return tmp;}
+
+CONSTCD14
+inline
+month&
+month::operator+=(const months& m) NOEXCEPT
+{
+    *this = *this + m;
+    return *this;
+}
+
+CONSTCD14
+inline
+month&
+month::operator-=(const months& m) NOEXCEPT
+{
+    *this = *this - m;
+    return *this;
+}
+
+CONSTCD11 inline month::operator unsigned() const NOEXCEPT {return m_;}
+CONSTCD11 inline bool month::ok() const NOEXCEPT {return 1 <= m_ && m_ <= 12;}
+
+CONSTCD11
+inline
+bool
+operator==(const month& x, const month& y) NOEXCEPT
+{
+    return static_cast<unsigned>(x) == static_cast<unsigned>(y);
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const month& x, const month& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+CONSTCD11
+inline
+bool
+operator<(const month& x, const month& y) NOEXCEPT
+{
+    return static_cast<unsigned>(x) < static_cast<unsigned>(y);
+}
+
+CONSTCD11
+inline
+bool
+operator>(const month& x, const month& y) NOEXCEPT
+{
+    return y < x;
+}
+
+CONSTCD11
+inline
+bool
+operator<=(const month& x, const month& y) NOEXCEPT
+{
+    return !(y < x);
+}
+
+CONSTCD11
+inline
+bool
+operator>=(const month& x, const month& y) NOEXCEPT
+{
+    return !(x < y);
+}
+
+CONSTCD14
+inline
+months
+operator-(const month& x, const month& y) NOEXCEPT
+{
+    auto const d = static_cast<unsigned>(x) - static_cast<unsigned>(y);
+    return months(d <= 11 ? d : d + 12);
+}
+
+CONSTCD14
+inline
+month
+operator+(const month& x, const months& y) NOEXCEPT
+{
+    auto const mu = static_cast<long long>(static_cast<unsigned>(x)) - 1 + y.count();
+    auto const yr = (mu >= 0 ? mu : mu-11) / 12;
+    return month{static_cast<unsigned>(mu - yr * 12 + 1)};
+}
+
+CONSTCD14
+inline
+month
+operator+(const months& x, const month& y) NOEXCEPT
+{
+    return y + x;
+}
+
+CONSTCD14
+inline
+month
+operator-(const month& x, const months& y) NOEXCEPT
+{
+    return x + -y;
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const month& m)
+{
+    switch (static_cast<unsigned>(m))
+    {
+    case 1:
+        os << "Farvardin";
+        break;
+    case 2:
+        os << "Ordibehesht";
+        break;
+    case 3:
+        os << "Khordad";
+        break;
+    case 4:
+        os << "Tir";
+        break;
+    case 5:
+        os << "Mordad";
+        break;
+    case 6:
+        os << "Shahrivar";
+        break;
+    case 7:
+        os << "Mehr";
+        break;
+    case 8:
+        os << "Aban";
+        break;
+    case 9:
+        os << "Azar";
+        break;
+    case 10:
+        os << "Dey";
+        break;
+    case 11:
+        os << "Bahman";
+        break;
+    case 12:
+        os << "Esfand";
+        break;
+    default:
+        os << static_cast<unsigned>(m) << " is not a valid month";
+        break;
+    }
+    return os;
+}
+
+// year
+
+CONSTCD11 inline year::year(int y) NOEXCEPT : y_(static_cast<decltype(y_)>(y)) {}
+CONSTCD14 inline year& year::operator++() NOEXCEPT {++y_; return *this;}
+CONSTCD14 inline year year::operator++(int) NOEXCEPT {auto tmp(*this); ++(*this); return tmp;}
+CONSTCD14 inline year& year::operator--() NOEXCEPT {--y_; return *this;}
+CONSTCD14 inline year year::operator--(int) NOEXCEPT {auto tmp(*this); --(*this); return tmp;}
+CONSTCD14 inline year& year::operator+=(const years& y) NOEXCEPT {*this = *this + y; return *this;}
+CONSTCD14 inline year& year::operator-=(const years& y) NOEXCEPT {*this = *this - y; return *this;}
+
+CONSTCD14
+inline
+bool
+year::is_leap() const NOEXCEPT
+{
+  using namespace internal;
+  auto const y = static_cast<int>(y_)-475;
+  auto const era_d = static_cast<int>(y >= 0 ? y : y-years_in_era+1) / static_cast<double>(years_in_era);
+  auto const era = static_cast<int>(era_d);
+  auto const yoe = static_cast<unsigned>(y - era * years_in_era);
+
+  // Reference: https://www.timeanddate.com/date/iran-leap-year.html
+  // 29 + 33 + 33 + 33 = 128
+  // 22 * 128 + 4
+  auto const yoc = (yoe < (22 * 128)) ? ((yoe%128) < 29 ? yoe%128 : (yoe%128 - 29)%33) : yoe - (22 * 128) + 33;
+  return (yoc != 0 && (yoc%4)==0);
+}
+
+CONSTCD11 inline year::operator int() const NOEXCEPT {return y_;}
+CONSTCD11 inline bool year::ok() const NOEXCEPT {return true;}
+
+CONSTCD11
+inline
+year
+year::min() NOEXCEPT
+{
+    return year{std::numeric_limits<short>::min()};
+}
+
+CONSTCD11
+inline
+year
+year::max() NOEXCEPT
+{
+    return year{std::numeric_limits<short>::max()};
+}
+
+CONSTCD11
+inline
+bool
+operator==(const year& x, const year& y) NOEXCEPT
+{
+    return static_cast<int>(x) == static_cast<int>(y);
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const year& x, const year& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+CONSTCD11
+inline
+bool
+operator<(const year& x, const year& y) NOEXCEPT
+{
+    return static_cast<int>(x) < static_cast<int>(y);
+}
+
+CONSTCD11
+inline
+bool
+operator>(const year& x, const year& y) NOEXCEPT
+{
+    return y < x;
+}
+
+CONSTCD11
+inline
+bool
+operator<=(const year& x, const year& y) NOEXCEPT
+{
+    return !(y < x);
+}
+
+CONSTCD11
+inline
+bool
+operator>=(const year& x, const year& y) NOEXCEPT
+{
+    return !(x < y);
+}
+
+CONSTCD11
+inline
+years
+operator-(const year& x, const year& y) NOEXCEPT
+{
+    return years{static_cast<int>(x) - static_cast<int>(y)};
+}
+
+CONSTCD11
+inline
+year
+operator+(const year& x, const years& y) NOEXCEPT
+{
+    return year{static_cast<int>(x) + y.count()};
+}
+
+CONSTCD11
+inline
+year
+operator+(const years& x, const year& y) NOEXCEPT
+{
+    return y + x;
+}
+
+CONSTCD11
+inline
+year
+operator-(const year& x, const years& y) NOEXCEPT
+{
+    return year{static_cast<int>(x) - y.count()};
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year& y)
+{
+    date::detail::save_ostream<CharT, Traits> _(os);
+    os.fill('0');
+    os.flags(std::ios::dec | std::ios::internal);
+    os.width(4 + (y < year{0}));
+    os << static_cast<int>(y);
+    return os;
+}
+
+// weekday
+
+CONSTCD11
+inline
+unsigned char
+weekday::weekday_from_days(int z) NOEXCEPT
+{
+  auto u = static_cast<unsigned>(z);
+  return static_cast<unsigned char>(z >= -4 ? (u+4) % 7 : u % 7);
+}
+
+CONSTCD11
+inline
+weekday::weekday(unsigned wd) NOEXCEPT
+    : wd_(static_cast<decltype(wd_)>(wd != 7 ? wd : 0))
+    {}
+
+CONSTCD11
+inline
+weekday::weekday(const sys_days& dp) NOEXCEPT
+    : wd_(weekday_from_days(dp.time_since_epoch().count()))
+    {}
+
+CONSTCD11
+inline
+weekday::weekday(const local_days& dp) NOEXCEPT
+    : wd_(weekday_from_days(dp.time_since_epoch().count()))
+    {}
+
+CONSTCD14 inline weekday& weekday::operator++() NOEXCEPT {if (++wd_ == 7) wd_ = 0; return *this;}
+CONSTCD14 inline weekday weekday::operator++(int) NOEXCEPT {auto tmp(*this); ++(*this); return tmp;}
+CONSTCD14 inline weekday& weekday::operator--() NOEXCEPT {if (wd_-- == 0) wd_ = 6; return *this;}
+CONSTCD14 inline weekday weekday::operator--(int) NOEXCEPT {auto tmp(*this); --(*this); return tmp;}
+
+CONSTCD14
+inline
+weekday&
+weekday::operator+=(const days& d) NOEXCEPT
+{
+    *this = *this + d;
+    return *this;
+}
+
+CONSTCD14
+inline
+weekday&
+weekday::operator-=(const days& d) NOEXCEPT
+{
+    *this = *this - d;
+    return *this;
+}
+
+CONSTCD11
+inline
+weekday::operator unsigned() const NOEXCEPT
+{
+    return static_cast<unsigned>(wd_);
+}
+
+CONSTCD11 inline bool weekday::ok() const NOEXCEPT {return wd_ <= 6;}
+
+CONSTCD11
+inline
+bool
+operator==(const weekday& x, const weekday& y) NOEXCEPT
+{
+    return static_cast<unsigned>(x) == static_cast<unsigned>(y);
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const weekday& x, const weekday& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+CONSTCD14
+inline
+days
+operator-(const weekday& x, const weekday& y) NOEXCEPT
+{
+    auto const diff = static_cast<unsigned>(x) - static_cast<unsigned>(y);
+    return days{diff <= 6 ? diff : diff + 7};
+}
+
+CONSTCD14
+inline
+weekday
+operator+(const weekday& x, const days& y) NOEXCEPT
+{
+    auto const wdu = static_cast<long long>(static_cast<unsigned>(x)) + y.count();
+    auto const wk = (wdu >= 0 ? wdu : wdu-6) / 7;
+    return weekday{static_cast<unsigned>(wdu - wk * 7)};
+}
+
+CONSTCD14
+inline
+weekday
+operator+(const days& x, const weekday& y) NOEXCEPT
+{
+    return y + x;
+}
+
+CONSTCD14
+inline
+weekday
+operator-(const weekday& x, const days& y) NOEXCEPT
+{
+    return x + -y;
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const weekday& wd)
+{
+    switch (static_cast<unsigned>(wd))
+    {
+    case 0:
+        os << "Yekshanbe";
+        break;
+    case 1:
+        os << "Doshanbe";
+        break;
+    case 2:
+        os << "Seshanbe";
+        break;
+    case 3:
+        os << "Chaharshanbe";
+        break;
+    case 4:
+        os << "Panjshanbe";
+        break;
+    case 5:
+        os << "Adine";
+        break;
+    case 6:
+        os << "Shanbe";
+        break;
+    default:
+        os << static_cast<unsigned>(wd) << " is not a valid weekday";
+        break;
+    }
+    return os;
+}
+
+#if !defined(_MSC_VER) || (_MSC_VER >= 1900)
+inline namespace literals
+{
+
+CONSTCD11
+inline
+solar_hijri::day
+operator "" _d(unsigned long long d) NOEXCEPT
+{
+    return solar_hijri::day{static_cast<unsigned>(d)};
+}
+
+CONSTCD11
+inline
+solar_hijri::year
+operator "" _y(unsigned long long y) NOEXCEPT
+{
+    return solar_hijri::year(static_cast<int>(y));
+}
+#endif  // !defined(_MSC_VER) || (_MSC_VER >= 1900)
+
+CONSTDATA solar_hijri::last_spec last{};
+
+CONSTDATA solar_hijri::month far            {1};
+CONSTDATA solar_hijri::month ord            {2};
+CONSTDATA solar_hijri::month kho            {3};
+CONSTDATA solar_hijri::month tir            {4};
+CONSTDATA solar_hijri::month mor            {5};
+CONSTDATA solar_hijri::month sha            {6};
+CONSTDATA solar_hijri::month meh            {7};
+CONSTDATA solar_hijri::month aba            {8};
+CONSTDATA solar_hijri::month aza            {9};
+CONSTDATA solar_hijri::month dey            {10};
+CONSTDATA solar_hijri::month bah            {11};
+CONSTDATA solar_hijri::month esf            {12};
+
+CONSTDATA solar_hijri::month Farvardin      {1};
+CONSTDATA solar_hijri::month Ordibehesht    {2};
+CONSTDATA solar_hijri::month Khordad        {3};
+CONSTDATA solar_hijri::month Tir            {4};
+CONSTDATA solar_hijri::month Mordad         {5};
+CONSTDATA solar_hijri::month Shahrivar      {6};
+CONSTDATA solar_hijri::month Mehr           {7};
+CONSTDATA solar_hijri::month Aban           {8};
+CONSTDATA solar_hijri::month Azar           {9};
+CONSTDATA solar_hijri::month Dey            {10};
+CONSTDATA solar_hijri::month Bahman         {11};
+CONSTDATA solar_hijri::month Esfand         {12};
+
+CONSTDATA solar_hijri::weekday yek          {0u};
+CONSTDATA solar_hijri::weekday dos          {1u};
+CONSTDATA solar_hijri::weekday ses          {2u};
+CONSTDATA solar_hijri::weekday cha          {3u};
+CONSTDATA solar_hijri::weekday pan          {4u};
+CONSTDATA solar_hijri::weekday adi          {5u};
+CONSTDATA solar_hijri::weekday shn          {6u};
+
+CONSTDATA solar_hijri::weekday Yekshanbe    {0u};
+CONSTDATA solar_hijri::weekday Doshanbe     {1u};
+CONSTDATA solar_hijri::weekday Seshanbe     {2u};
+CONSTDATA solar_hijri::weekday Chaharshanbe {3u};
+CONSTDATA solar_hijri::weekday Panjshanbe   {4u};
+CONSTDATA solar_hijri::weekday Adine        {5u};
+CONSTDATA solar_hijri::weekday Shanbe       {6u};
+
+#if !defined(_MSC_VER) || (_MSC_VER >= 1900)
+}  // inline namespace literals
+#endif
+
+// weekday_indexed
+
+CONSTCD11
+inline
+weekday
+weekday_indexed::weekday() const NOEXCEPT
+{
+    return solar_hijri::weekday{static_cast<unsigned>(wd_)};
+}
+
+CONSTCD11 inline unsigned weekday_indexed::index() const NOEXCEPT {return index_;}
+
+CONSTCD11
+inline
+bool
+weekday_indexed::ok() const NOEXCEPT
+{
+    return weekday().ok() && 1 <= index_ && index_ <= 5;
+}
+
+CONSTCD11
+inline
+weekday_indexed::weekday_indexed(const solar_hijri::weekday& wd, unsigned index) NOEXCEPT
+    : wd_(static_cast<decltype(wd_)>(static_cast<unsigned>(wd)))
+    , index_(static_cast<decltype(index_)>(index))
+    {}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const weekday_indexed& wdi)
+{
+    return os << wdi.weekday() << '[' << wdi.index() << ']';
+}
+
+CONSTCD11
+inline
+weekday_indexed
+weekday::operator[](unsigned index) const NOEXCEPT
+{
+    return {*this, index};
+}
+
+CONSTCD11
+inline
+bool
+operator==(const weekday_indexed& x, const weekday_indexed& y) NOEXCEPT
+{
+    return x.weekday() == y.weekday() && x.index() == y.index();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const weekday_indexed& x, const weekday_indexed& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+// weekday_last
+
+CONSTCD11 inline solar_hijri::weekday weekday_last::weekday() const NOEXCEPT {return wd_;}
+CONSTCD11 inline bool weekday_last::ok() const NOEXCEPT {return wd_.ok();}
+CONSTCD11 inline weekday_last::weekday_last(const solar_hijri::weekday& wd) NOEXCEPT : wd_(wd) {}
+
+CONSTCD11
+inline
+bool
+operator==(const weekday_last& x, const weekday_last& y) NOEXCEPT
+{
+    return x.weekday() == y.weekday();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const weekday_last& x, const weekday_last& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const weekday_last& wdl)
+{
+    return os << wdl.weekday() << "[last]";
+}
+
+CONSTCD11
+inline
+weekday_last
+weekday::operator[](last_spec) const NOEXCEPT
+{
+    return weekday_last{*this};
+}
+
+// year_month
+
+CONSTCD11
+inline
+year_month::year_month(const solar_hijri::year& y, const solar_hijri::month& m) NOEXCEPT
+    : y_(y)
+    , m_(m)
+    {}
+
+CONSTCD11 inline year year_month::year() const NOEXCEPT {return y_;}
+CONSTCD11 inline month year_month::month() const NOEXCEPT {return m_;}
+CONSTCD11 inline bool year_month::ok() const NOEXCEPT {return y_.ok() && m_.ok();}
+
+CONSTCD14
+inline
+year_month&
+year_month::operator+=(const months& dm) NOEXCEPT
+{
+    *this = *this + dm;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month&
+year_month::operator-=(const months& dm) NOEXCEPT
+{
+    *this = *this - dm;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month&
+year_month::operator+=(const years& dy) NOEXCEPT
+{
+    *this = *this + dy;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month&
+year_month::operator-=(const years& dy) NOEXCEPT
+{
+    *this = *this - dy;
+    return *this;
+}
+
+CONSTCD11
+inline
+bool
+operator==(const year_month& x, const year_month& y) NOEXCEPT
+{
+    return x.year() == y.year() && x.month() == y.month();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const year_month& x, const year_month& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+CONSTCD11
+inline
+bool
+operator<(const year_month& x, const year_month& y) NOEXCEPT
+{
+    return x.year() < y.year() ? true
+        : (x.year() > y.year() ? false
+        : (x.month() < y.month()));
+}
+
+CONSTCD11
+inline
+bool
+operator>(const year_month& x, const year_month& y) NOEXCEPT
+{
+    return y < x;
+}
+
+CONSTCD11
+inline
+bool
+operator<=(const year_month& x, const year_month& y) NOEXCEPT
+{
+    return !(y < x);
+}
+
+CONSTCD11
+inline
+bool
+operator>=(const year_month& x, const year_month& y) NOEXCEPT
+{
+    return !(x < y);
+}
+
+CONSTCD14
+inline
+year_month
+operator+(const year_month& ym, const months& dm) NOEXCEPT
+{
+    auto dmi = static_cast<int>(static_cast<unsigned>(ym.month())) - 1 + dm.count();
+    auto dy = (dmi >= 0 ? dmi : dmi-11) / 12;
+    dmi = dmi - dy * 12 + 1;
+    return (ym.year() + years(dy)) / month(static_cast<unsigned>(dmi));
+}
+
+CONSTCD14
+inline
+year_month
+operator+(const months& dm, const year_month& ym) NOEXCEPT
+{
+    return ym + dm;
+}
+
+CONSTCD14
+inline
+year_month
+operator-(const year_month& ym, const months& dm) NOEXCEPT
+{
+    return ym + -dm;
+}
+
+CONSTCD11
+inline
+months
+operator-(const year_month& x, const year_month& y) NOEXCEPT
+{
+    return (x.year() - y.year()) +
+            months(static_cast<unsigned>(x.month()) - static_cast<unsigned>(y.month()));
+}
+
+CONSTCD11
+inline
+year_month
+operator+(const year_month& ym, const years& dy) NOEXCEPT
+{
+    return (ym.year() + dy) / ym.month();
+}
+
+CONSTCD11
+inline
+year_month
+operator+(const years& dy, const year_month& ym) NOEXCEPT
+{
+    return ym + dy;
+}
+
+CONSTCD11
+inline
+year_month
+operator-(const year_month& ym, const years& dy) NOEXCEPT
+{
+    return ym + -dy;
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_month& ym)
+{
+    return os << ym.year() << '/' << ym.month();
+}
+
+// month_day
+
+CONSTCD11
+inline
+month_day::month_day(const solar_hijri::month& m, const solar_hijri::day& d) NOEXCEPT
+    : m_(m)
+    , d_(d)
+    {}
+
+CONSTCD11 inline solar_hijri::month month_day::month() const NOEXCEPT {return m_;}
+CONSTCD11 inline solar_hijri::day month_day::day() const NOEXCEPT {return d_;}
+
+CONSTCD14
+inline
+bool
+month_day::ok() const NOEXCEPT
+{
+    CONSTDATA solar_hijri::day d[] = { 
+        solar_hijri::day(31), solar_hijri::day(31), solar_hijri::day(31), 
+        solar_hijri::day(31), solar_hijri::day(31), solar_hijri::day(31), 
+        solar_hijri::day(30), solar_hijri::day(30), solar_hijri::day(30), 
+        solar_hijri::day(30), solar_hijri::day(30), solar_hijri::day(30) 
+    };
+    return m_.ok() && solar_hijri::day(1) <= d_ && d_ <= d[static_cast<unsigned>(m_)-1];
+}
+
+CONSTCD11
+inline
+bool
+operator==(const month_day& x, const month_day& y) NOEXCEPT
+{
+    return x.month() == y.month() && x.day() == y.day();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const month_day& x, const month_day& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+CONSTCD11
+inline
+bool
+operator<(const month_day& x, const month_day& y) NOEXCEPT
+{
+    return x.month() < y.month() ? true
+        : (x.month() > y.month() ? false
+        : (x.day() < y.day()));
+}
+
+CONSTCD11
+inline
+bool
+operator>(const month_day& x, const month_day& y) NOEXCEPT
+{
+    return y < x;
+}
+
+CONSTCD11
+inline
+bool
+operator<=(const month_day& x, const month_day& y) NOEXCEPT
+{
+    return !(y < x);
+}
+
+CONSTCD11
+inline
+bool
+operator>=(const month_day& x, const month_day& y) NOEXCEPT
+{
+    return !(x < y);
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const month_day& md)
+{
+    return os << md.month() << '/' << md.day();
+}
+
+// month_day_last
+
+CONSTCD11 inline month month_day_last::month() const NOEXCEPT {return m_;}
+CONSTCD11 inline bool month_day_last::ok() const NOEXCEPT {return m_.ok();}
+CONSTCD11 inline month_day_last::month_day_last(const solar_hijri::month& m) NOEXCEPT : m_(m) {}
+
+CONSTCD11
+inline
+bool
+operator==(const month_day_last& x, const month_day_last& y) NOEXCEPT
+{
+    return x.month() == y.month();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const month_day_last& x, const month_day_last& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+CONSTCD11
+inline
+bool
+operator<(const month_day_last& x, const month_day_last& y) NOEXCEPT
+{
+    return x.month() < y.month();
+}
+
+CONSTCD11
+inline
+bool
+operator>(const month_day_last& x, const month_day_last& y) NOEXCEPT
+{
+    return y < x;
+}
+
+CONSTCD11
+inline
+bool
+operator<=(const month_day_last& x, const month_day_last& y) NOEXCEPT
+{
+    return !(y < x);
+}
+
+CONSTCD11
+inline
+bool
+operator>=(const month_day_last& x, const month_day_last& y) NOEXCEPT
+{
+    return !(x < y);
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const month_day_last& mdl)
+{
+    return os << mdl.month() << "/last";
+}
+
+// month_weekday
+
+CONSTCD11
+inline
+month_weekday::month_weekday(const solar_hijri::month& m,
+                             const solar_hijri::weekday_indexed& wdi) NOEXCEPT
+    : m_(m)
+    , wdi_(wdi)
+    {}
+
+CONSTCD11 inline month month_weekday::month() const NOEXCEPT {return m_;}
+
+CONSTCD11
+inline
+weekday_indexed
+month_weekday::weekday_indexed() const NOEXCEPT
+{
+    return wdi_;
+}
+
+CONSTCD11
+inline
+bool
+month_weekday::ok() const NOEXCEPT
+{
+    return m_.ok() && wdi_.ok();
+}
+
+CONSTCD11
+inline
+bool
+operator==(const month_weekday& x, const month_weekday& y) NOEXCEPT
+{
+    return x.month() == y.month() && x.weekday_indexed() == y.weekday_indexed();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const month_weekday& x, const month_weekday& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const month_weekday& mwd)
+{
+    return os << mwd.month() << '/' << mwd.weekday_indexed();
+}
+
+// month_weekday_last
+
+CONSTCD11
+inline
+month_weekday_last::month_weekday_last(const solar_hijri::month& m,
+                                       const solar_hijri::weekday_last& wdl) NOEXCEPT
+    : m_(m)
+    , wdl_(wdl)
+    {}
+
+CONSTCD11 inline month month_weekday_last::month() const NOEXCEPT {return m_;}
+
+CONSTCD11
+inline
+weekday_last
+month_weekday_last::weekday_last() const NOEXCEPT
+{
+    return wdl_;
+}
+
+CONSTCD11
+inline
+bool
+month_weekday_last::ok() const NOEXCEPT
+{
+    return m_.ok() && wdl_.ok();
+}
+
+CONSTCD11
+inline
+bool
+operator==(const month_weekday_last& x, const month_weekday_last& y) NOEXCEPT
+{
+    return x.month() == y.month() && x.weekday_last() == y.weekday_last();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const month_weekday_last& x, const month_weekday_last& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const month_weekday_last& mwdl)
+{
+    return os << mwdl.month() << '/' << mwdl.weekday_last();
+}
+
+// year_month_day_last
+
+CONSTCD11
+inline
+year_month_day_last::year_month_day_last(const solar_hijri::year& y,
+                                         const solar_hijri::month_day_last& mdl) NOEXCEPT
+    : y_(y)
+    , mdl_(mdl)
+    {}
+
+CONSTCD14
+inline
+year_month_day_last&
+year_month_day_last::operator+=(const months& m) NOEXCEPT
+{
+    *this = *this + m;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month_day_last&
+year_month_day_last::operator-=(const months& m) NOEXCEPT
+{
+    *this = *this - m;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month_day_last&
+year_month_day_last::operator+=(const years& y) NOEXCEPT
+{
+    *this = *this + y;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month_day_last&
+year_month_day_last::operator-=(const years& y) NOEXCEPT
+{
+    *this = *this - y;
+    return *this;
+}
+
+CONSTCD11 inline year year_month_day_last::year() const NOEXCEPT {return y_;}
+CONSTCD11 inline month year_month_day_last::month() const NOEXCEPT {return mdl_.month();}
+
+CONSTCD11
+inline
+month_day_last
+year_month_day_last::month_day_last() const NOEXCEPT
+{
+    return mdl_;
+}
+
+CONSTCD14
+inline
+day
+year_month_day_last::day() const NOEXCEPT
+{
+    CONSTDATA solar_hijri::day d[] = { 
+        solar_hijri::day(31), solar_hijri::day(31), solar_hijri::day(31), 
+        solar_hijri::day(31), solar_hijri::day(31), solar_hijri::day(31), 
+        solar_hijri::day(30), solar_hijri::day(30), solar_hijri::day(30), 
+        solar_hijri::day(30), solar_hijri::day(30), solar_hijri::day(29) 
+    };
+    return month() != esf || !y_.is_leap() ?
+        d[static_cast<unsigned>(month()) - 1] : solar_hijri::day(30);
+}
+
+CONSTCD14
+inline
+year_month_day_last::operator sys_days() const NOEXCEPT
+{
+    return sys_days(year()/month()/day());
+}
+
+CONSTCD14
+inline
+year_month_day_last::operator local_days() const NOEXCEPT
+{
+    return local_days(year()/month()/day());
+}
+
+CONSTCD11
+inline
+bool
+year_month_day_last::ok() const NOEXCEPT
+{
+    return y_.ok() && mdl_.ok();
+}
+
+CONSTCD11
+inline
+bool
+operator==(const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT
+{
+    return x.year() == y.year() && x.month_day_last() == y.month_day_last();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+CONSTCD11
+inline
+bool
+operator<(const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT
+{
+    return x.year() < y.year() ? true
+        : (x.year() > y.year() ? false
+        : (x.month_day_last() < y.month_day_last()));
+}
+
+CONSTCD11
+inline
+bool
+operator>(const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT
+{
+    return y < x;
+}
+
+CONSTCD11
+inline
+bool
+operator<=(const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT
+{
+    return !(y < x);
+}
+
+CONSTCD11
+inline
+bool
+operator>=(const year_month_day_last& x, const year_month_day_last& y) NOEXCEPT
+{
+    return !(x < y);
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_month_day_last& ymdl)
+{
+    return os << ymdl.year() << '/' << ymdl.month_day_last();
+}
+
+CONSTCD14
+inline
+year_month_day_last
+operator+(const year_month_day_last& ymdl, const months& dm) NOEXCEPT
+{
+    return (ymdl.year() / ymdl.month() + dm) / last;
+}
+
+CONSTCD14
+inline
+year_month_day_last
+operator+(const months& dm, const year_month_day_last& ymdl) NOEXCEPT
+{
+    return ymdl + dm;
+}
+
+CONSTCD14
+inline
+year_month_day_last
+operator-(const year_month_day_last& ymdl, const months& dm) NOEXCEPT
+{
+    return ymdl + (-dm);
+}
+
+CONSTCD11
+inline
+year_month_day_last
+operator+(const year_month_day_last& ymdl, const years& dy) NOEXCEPT
+{
+    return {ymdl.year()+dy, ymdl.month_day_last()};
+}
+
+CONSTCD11
+inline
+year_month_day_last
+operator+(const years& dy, const year_month_day_last& ymdl) NOEXCEPT
+{
+    return ymdl + dy;
+}
+
+CONSTCD11
+inline
+year_month_day_last
+operator-(const year_month_day_last& ymdl, const years& dy) NOEXCEPT
+{
+    return ymdl + (-dy);
+}
+
+// year_month_day
+
+CONSTCD11
+inline
+year_month_day::year_month_day(const solar_hijri::year& y, const solar_hijri::month& m,
+                               const solar_hijri::day& d) NOEXCEPT
+    : y_(y)
+    , m_(m)
+    , d_(d)
+    {}
+
+CONSTCD14
+inline
+year_month_day::year_month_day(const year_month_day_last& ymdl) NOEXCEPT
+    : y_(ymdl.year())
+    , m_(ymdl.month())
+    , d_(ymdl.day())
+    {}
+
+CONSTCD14
+inline
+year_month_day::year_month_day(sys_days dp) NOEXCEPT
+    : year_month_day(from_days(dp.time_since_epoch()))
+    {}
+
+CONSTCD14
+inline
+year_month_day::year_month_day(local_days dp) NOEXCEPT
+    : year_month_day(from_days(dp.time_since_epoch()))
+    {}
+
+CONSTCD11 inline year year_month_day::year() const NOEXCEPT {return y_;}
+CONSTCD11 inline month year_month_day::month() const NOEXCEPT {return m_;}
+CONSTCD11 inline day year_month_day::day() const NOEXCEPT {return d_;}
+
+CONSTCD14
+inline
+year_month_day&
+year_month_day::operator+=(const months& m) NOEXCEPT
+{
+    *this = *this + m;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month_day&
+year_month_day::operator-=(const months& m) NOEXCEPT
+{
+    *this = *this - m;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month_day&
+year_month_day::operator+=(const years& y) NOEXCEPT
+{
+    *this = *this + y;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month_day&
+year_month_day::operator-=(const years& y) NOEXCEPT
+{
+    *this = *this - y;
+    return *this;
+}
+
+CONSTCD14
+inline
+days
+year_month_day::to_days() const NOEXCEPT
+{
+    static_assert(std::numeric_limits<unsigned>::digits >= 18,
+             "This algorithm has not been ported to a 16 bit unsigned integer");
+    static_assert(std::numeric_limits<int>::digits >= 20,
+             "This algorithm has not been ported to a 16 bit signed integer");
+
+    using namespace internal;
+    auto const y = static_cast<int>(y_) - 475;
+    auto const m = static_cast<unsigned>(m_);
+    auto const d = static_cast<unsigned>(d_);
+    auto const era_d = static_cast<int>(y >= 0 ? y : y-years_in_era+1) / static_cast<double>(years_in_era);
+    auto const era = static_cast<int>(era_d);
+    auto const fdoe = static_cast<int>(epoch + era * days_in_era);
+    auto const yoe = static_cast<int>(y - era * years_in_era);
+
+    auto const period_d = static_cast<double>(yoe/years_in_period);
+    auto const period = static_cast<unsigned>(period_d);
+    auto const yop = yoe%years_in_period;
+    auto const fdop = period*days_in_period;
+    auto const cycle = yop < 29 ? 0 : static_cast<unsigned>((yop-29)/years_in_other_cycles + 1);
+    auto const yoc = yop < 29 ? yop : (yop-29)%years_in_other_cycles;
+    auto const fdoc = cycle > 0 ? days_in_first_cycle + (cycle-1)*days_in_other_cycles : 0;
+    auto const group = yoc < 1 ? 0 : static_cast<unsigned>((yoc-1) / 4);
+    auto const yog = static_cast<int>(yoc < 1 ? -1 : (yoc-1) % 4);
+    auto const fdoyog = group*1461 + (yog+1)*365;
+    auto const fdoyoe = fdop + fdoc + fdoyog;
+
+    auto const doy = 30*(m-1) + ((m > 6) ? 6 : m-1) + d-1;                     // [0, 365]
+    auto const doe = fdoe + fdoyoe + doy;
+    return days{doe - unix_time_shift};
+}
+
+CONSTCD14
+inline
+year_month_day::operator sys_days() const NOEXCEPT
+{
+    return sys_days{to_days()};
+}
+
+CONSTCD14
+inline
+year_month_day::operator local_days() const NOEXCEPT
+{
+    return local_days{to_days()};
+}
+
+CONSTCD14
+inline
+bool
+year_month_day::ok() const NOEXCEPT
+{
+    if (!(y_.ok() && m_.ok()))
+        return false;
+    return solar_hijri::day(1) <= d_ && d_ <= (y_/m_/last).day();
+}
+
+CONSTCD11
+inline
+bool
+operator==(const year_month_day& x, const year_month_day& y) NOEXCEPT
+{
+    return x.year() == y.year() && x.month() == y.month() && x.day() == y.day();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const year_month_day& x, const year_month_day& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+CONSTCD11
+inline
+bool
+operator<(const year_month_day& x, const year_month_day& y) NOEXCEPT
+{
+    return x.year() < y.year() ? true
+        : (x.year() > y.year() ? false
+        : (x.month() < y.month() ? true
+        : (x.month() > y.month() ? false
+        : (x.day() < y.day()))));
+}
+
+CONSTCD11
+inline
+bool
+operator>(const year_month_day& x, const year_month_day& y) NOEXCEPT
+{
+    return y < x;
+}
+
+CONSTCD11
+inline
+bool
+operator<=(const year_month_day& x, const year_month_day& y) NOEXCEPT
+{
+    return !(y < x);
+}
+
+CONSTCD11
+inline
+bool
+operator>=(const year_month_day& x, const year_month_day& y) NOEXCEPT
+{
+    return !(x < y);
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_month_day& ymd)
+{
+    date::detail::save_ostream<CharT, Traits> _(os);
+    os.fill('0');
+    os.flags(std::ios::dec | std::ios::right);
+    os << ymd.year() << '-';
+    os.width(2);
+    os << static_cast<unsigned>(ymd.month()) << '-';
+    os << ymd.day();
+    return os;
+}
+
+CONSTCD14
+inline
+year_month_day
+year_month_day::from_days(days dp) NOEXCEPT
+{
+    static_assert(std::numeric_limits<unsigned>::digits >= 18,
+             "This algorithm has not been ported to a 16 bit unsigned integer");
+    static_assert(std::numeric_limits<int>::digits >= 20,
+             "This algorithm has not been ported to a 16 bit signed integer");
+
+    using namespace internal;
+    auto const z = dp.count() + unix_time_shift;
+    auto const delta = static_cast<int>(z - epoch);
+    auto const era = static_cast<int>(delta >= 0 ? delta : delta-days_in_era+1) / static_cast<double>(days_in_era);
+    auto const era_i = static_cast<int>(era);
+    auto const fdoe = static_cast<int>(epoch + static_cast<int>(era_i * days_in_era));
+
+    auto const doe_fdoe = z - fdoe;
+    auto const period = static_cast<unsigned>(doe_fdoe < 22*days_in_period ? doe_fdoe / days_in_period : 22);
+    auto const dop = doe_fdoe % days_in_period;
+    auto const cycle = dop < days_in_first_cycle ? 0 : (dop-days_in_first_cycle) / days_in_other_cycles + 1;
+    auto const doc = dop < days_in_first_cycle ? dop : (dop-days_in_first_cycle) % days_in_other_cycles;
+    auto const group = doc < 365 && period != 22 ? -1 : static_cast<int>(((doc < 365 ? 365 : doc)-365)/1461);
+    auto const yog =   doc < 365 && period != 22 ? -1 : static_cast<int>( (period != 22 ? ((doc-365 )%1461) : doc)/365);
+    auto const yoc = group == -1 ?  0 : (period != 22 ? 1 : 0) + group*4 + (yog == 4 ? 3 : yog);
+    auto const doy = group == -1 ? doc : (period != 22 ? ((yoc-1)%4 == 0 ? (group >= 0 ? (doe_fdoe -
+                                                                                         (period*days_in_period) -
+                                                                                         (cycle > 0 ? days_in_first_cycle + (cycle-1)*days_in_other_cycles : 0) -
+                                                                                         (group*1461 + ((yog == 4 ? 3 : yog)+1)*365))
+                                                                                      : 365)
+                                                                         : doe_fdoe -
+                                                                           (period*days_in_period) -
+                                                                           (cycle > 0 ? days_in_first_cycle + (cycle-1)*days_in_other_cycles : 0) -
+                                                                           (group*1461 + ((yog == 4 ? 3 : yog)+1)*365))
+                                                       : (yog == 4 ? 365 : doe_fdoe - (period*days_in_period) - yog*365));
+    auto const yoe = period != 22 ? period*years_in_period +
+                                    (cycle > 0 ? years_in_first_cycle +
+                                                (cycle-1)*years_in_other_cycles
+                                              : 0) +
+                                    yoc
+                                  : 22*years_in_period + ((yog == 4) ? 3 : yog);
+    auto const y = static_cast<int>(static_cast<sys_days::rep>(yoe) + 475 + era_i * years_in_era);
+    auto const m = doy < 186 ? doy/31 + 1 : (doy-186)/30 + 7;           // [1, 12]
+    auto const d = doy - (30*(m-1) + ((m > 6) ? 6 : m-1) - 1);          // [1, 31]
+
+    return year_month_day{solar_hijri::year(y), solar_hijri::month(m), solar_hijri::day(d)};
+}
+
+CONSTCD14
+inline
+year_month_day
+operator+(const year_month_day& ymd, const months& dm) NOEXCEPT
+{
+    return (ymd.year() / ymd.month() + dm) / ymd.day();
+}
+
+CONSTCD14
+inline
+year_month_day
+operator+(const months& dm, const year_month_day& ymd) NOEXCEPT
+{
+    return ymd + dm;
+}
+
+CONSTCD14
+inline
+year_month_day
+operator-(const year_month_day& ymd, const months& dm) NOEXCEPT
+{
+    return ymd + (-dm);
+}
+
+CONSTCD11
+inline
+year_month_day
+operator+(const year_month_day& ymd, const years& dy) NOEXCEPT
+{
+    return (ymd.year() + dy) / ymd.month() / ymd.day();
+}
+
+CONSTCD11
+inline
+year_month_day
+operator+(const years& dy, const year_month_day& ymd) NOEXCEPT
+{
+    return ymd + dy;
+}
+
+CONSTCD11
+inline
+year_month_day
+operator-(const year_month_day& ymd, const years& dy) NOEXCEPT
+{
+    return ymd + (-dy);
+}
+
+// year_month_weekday
+
+CONSTCD11
+inline
+year_month_weekday::year_month_weekday(const solar_hijri::year& y, const solar_hijri::month& m,
+                                       const solar_hijri::weekday_indexed& wdi)
+        NOEXCEPT
+    : y_(y)
+    , m_(m)
+    , wdi_(wdi)
+    {}
+
+CONSTCD14
+inline
+year_month_weekday::year_month_weekday(const sys_days& dp) NOEXCEPT
+    : year_month_weekday(from_days(dp.time_since_epoch()))
+    {}
+
+CONSTCD14
+inline
+year_month_weekday::year_month_weekday(const local_days& dp) NOEXCEPT
+    : year_month_weekday(from_days(dp.time_since_epoch()))
+    {}
+
+CONSTCD14
+inline
+year_month_weekday&
+year_month_weekday::operator+=(const months& m) NOEXCEPT
+{
+    *this = *this + m;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month_weekday&
+year_month_weekday::operator-=(const months& m) NOEXCEPT
+{
+    *this = *this - m;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month_weekday&
+year_month_weekday::operator+=(const years& y) NOEXCEPT
+{
+    *this = *this + y;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month_weekday&
+year_month_weekday::operator-=(const years& y) NOEXCEPT
+{
+    *this = *this - y;
+    return *this;
+}
+
+CONSTCD11 inline year year_month_weekday::year() const NOEXCEPT {return y_;}
+CONSTCD11 inline month year_month_weekday::month() const NOEXCEPT {return m_;}
+
+CONSTCD11
+inline
+weekday
+year_month_weekday::weekday() const NOEXCEPT
+{
+    return wdi_.weekday();
+}
+
+CONSTCD11
+inline
+unsigned
+year_month_weekday::index() const NOEXCEPT
+{
+    return wdi_.index();
+}
+
+CONSTCD11
+inline
+weekday_indexed
+year_month_weekday::weekday_indexed() const NOEXCEPT
+{
+    return wdi_;
+}
+
+CONSTCD14
+inline
+year_month_weekday::operator sys_days() const NOEXCEPT
+{
+    return sys_days{to_days()};
+}
+
+CONSTCD14
+inline
+year_month_weekday::operator local_days() const NOEXCEPT
+{
+    return local_days{to_days()};
+}
+
+CONSTCD14
+inline
+bool
+year_month_weekday::ok() const NOEXCEPT
+{
+    if (!y_.ok() || !m_.ok() || !wdi_.weekday().ok() || wdi_.index() < 1)
+        return false;
+    if (wdi_.index() <= 4)
+        return true;
+    auto d2 = wdi_.weekday() - solar_hijri::weekday(y_/m_/1) + days((wdi_.index()-1)*7 + 1);
+    return static_cast<unsigned>(d2.count()) <= static_cast<unsigned>((y_/m_/last).day());
+}
+
+CONSTCD14
+inline
+year_month_weekday
+year_month_weekday::from_days(days d) NOEXCEPT
+{
+    sys_days dp{d};
+    auto const wd = solar_hijri::weekday(dp);
+    auto const ymd = year_month_day(dp);
+    return {ymd.year(), ymd.month(), wd[(static_cast<unsigned>(ymd.day())-1)/7+1]};
+}
+
+CONSTCD14
+inline
+days
+year_month_weekday::to_days() const NOEXCEPT
+{
+    auto d = sys_days(y_/m_/1);
+    return (d + (wdi_.weekday() - solar_hijri::weekday(d) + days{(wdi_.index()-1)*7})
+           ).time_since_epoch();
+}
+
+CONSTCD11
+inline
+bool
+operator==(const year_month_weekday& x, const year_month_weekday& y) NOEXCEPT
+{
+    return x.year() == y.year() && x.month() == y.month() &&
+           x.weekday_indexed() == y.weekday_indexed();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const year_month_weekday& x, const year_month_weekday& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_month_weekday& ymwdi)
+{
+    return os << ymwdi.year() << '/' << ymwdi.month()
+              << '/' << ymwdi.weekday_indexed();
+}
+
+CONSTCD14
+inline
+year_month_weekday
+operator+(const year_month_weekday& ymwd, const months& dm) NOEXCEPT
+{
+    return (ymwd.year() / ymwd.month() + dm) / ymwd.weekday_indexed();
+}
+
+CONSTCD14
+inline
+year_month_weekday
+operator+(const months& dm, const year_month_weekday& ymwd) NOEXCEPT
+{
+    return ymwd + dm;
+}
+
+CONSTCD14
+inline
+year_month_weekday
+operator-(const year_month_weekday& ymwd, const months& dm) NOEXCEPT
+{
+    return ymwd + (-dm);
+}
+
+CONSTCD11
+inline
+year_month_weekday
+operator+(const year_month_weekday& ymwd, const years& dy) NOEXCEPT
+{
+    return {ymwd.year()+dy, ymwd.month(), ymwd.weekday_indexed()};
+}
+
+CONSTCD11
+inline
+year_month_weekday
+operator+(const years& dy, const year_month_weekday& ymwd) NOEXCEPT
+{
+    return ymwd + dy;
+}
+
+CONSTCD11
+inline
+year_month_weekday
+operator-(const year_month_weekday& ymwd, const years& dy) NOEXCEPT
+{
+    return ymwd + (-dy);
+}
+
+// year_month_weekday_last
+
+CONSTCD11
+inline
+year_month_weekday_last::year_month_weekday_last(const solar_hijri::year& y,
+                                                 const solar_hijri::month& m,
+                                                 const solar_hijri::weekday_last& wdl) NOEXCEPT
+    : y_(y)
+    , m_(m)
+    , wdl_(wdl)
+    {}
+
+CONSTCD14
+inline
+year_month_weekday_last&
+year_month_weekday_last::operator+=(const months& m) NOEXCEPT
+{
+    *this = *this + m;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month_weekday_last&
+year_month_weekday_last::operator-=(const months& m) NOEXCEPT
+{
+    *this = *this - m;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month_weekday_last&
+year_month_weekday_last::operator+=(const years& y) NOEXCEPT
+{
+    *this = *this + y;
+    return *this;
+}
+
+CONSTCD14
+inline
+year_month_weekday_last&
+year_month_weekday_last::operator-=(const years& y) NOEXCEPT
+{
+    *this = *this - y;
+    return *this;
+}
+
+CONSTCD11 inline year year_month_weekday_last::year() const NOEXCEPT {return y_;}
+CONSTCD11 inline month year_month_weekday_last::month() const NOEXCEPT {return m_;}
+
+CONSTCD11
+inline
+weekday
+year_month_weekday_last::weekday() const NOEXCEPT
+{
+    return wdl_.weekday();
+}
+
+CONSTCD11
+inline
+weekday_last
+year_month_weekday_last::weekday_last() const NOEXCEPT
+{
+    return wdl_;
+}
+
+CONSTCD14
+inline
+year_month_weekday_last::operator sys_days() const NOEXCEPT
+{
+    return sys_days{to_days()};
+}
+
+CONSTCD14
+inline
+year_month_weekday_last::operator local_days() const NOEXCEPT
+{
+    return local_days{to_days()};
+}
+
+CONSTCD11
+inline
+bool
+year_month_weekday_last::ok() const NOEXCEPT
+{
+    return y_.ok() && m_.ok() && wdl_.ok();
+}
+
+CONSTCD14
+inline
+days
+year_month_weekday_last::to_days() const NOEXCEPT
+{
+    auto const d = sys_days(y_/m_/last);
+    return (d - (solar_hijri::weekday{d} - wdl_.weekday())).time_since_epoch();
+}
+
+CONSTCD11
+inline
+bool
+operator==(const year_month_weekday_last& x, const year_month_weekday_last& y) NOEXCEPT
+{
+    return x.year() == y.year() && x.month() == y.month() &&
+           x.weekday_last() == y.weekday_last();
+}
+
+CONSTCD11
+inline
+bool
+operator!=(const year_month_weekday_last& x, const year_month_weekday_last& y) NOEXCEPT
+{
+    return !(x == y);
+}
+
+template<class CharT, class Traits>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const year_month_weekday_last& ymwdl)
+{
+    return os << ymwdl.year() << '/' << ymwdl.month() << '/' << ymwdl.weekday_last();
+}
+
+CONSTCD14
+inline
+year_month_weekday_last
+operator+(const year_month_weekday_last& ymwdl, const months& dm) NOEXCEPT
+{
+    return (ymwdl.year() / ymwdl.month() + dm) / ymwdl.weekday_last();
+}
+
+CONSTCD14
+inline
+year_month_weekday_last
+operator+(const months& dm, const year_month_weekday_last& ymwdl) NOEXCEPT
+{
+    return ymwdl + dm;
+}
+
+CONSTCD14
+inline
+year_month_weekday_last
+operator-(const year_month_weekday_last& ymwdl, const months& dm) NOEXCEPT
+{
+    return ymwdl + (-dm);
+}
+
+CONSTCD11
+inline
+year_month_weekday_last
+operator+(const year_month_weekday_last& ymwdl, const years& dy) NOEXCEPT
+{
+    return {ymwdl.year()+dy, ymwdl.month(), ymwdl.weekday_last()};
+}
+
+CONSTCD11
+inline
+year_month_weekday_last
+operator+(const years& dy, const year_month_weekday_last& ymwdl) NOEXCEPT
+{
+    return ymwdl + dy;
+}
+
+CONSTCD11
+inline
+year_month_weekday_last
+operator-(const year_month_weekday_last& ymwdl, const years& dy) NOEXCEPT
+{
+    return ymwdl + (-dy);
+}
+
+// year_month from operator/()
+
+CONSTCD11
+inline
+year_month
+operator/(const year& y, const month& m) NOEXCEPT
+{
+    return {y, m};
+}
+
+CONSTCD11
+inline
+year_month
+operator/(const year& y, int   m) NOEXCEPT
+{
+    return y / month(static_cast<unsigned>(m));
+}
+
+// month_day from operator/()
+
+CONSTCD11
+inline
+month_day
+operator/(const month& m, const day& d) NOEXCEPT
+{
+    return {m, d};
+}
+
+CONSTCD11
+inline
+month_day
+operator/(const day& d, const month& m) NOEXCEPT
+{
+    return m / d;
+}
+
+CONSTCD11
+inline
+month_day
+operator/(const month& m, int d) NOEXCEPT
+{
+    return m / day(static_cast<unsigned>(d));
+}
+
+CONSTCD11
+inline
+month_day
+operator/(int m, const day& d) NOEXCEPT
+{
+    return month(static_cast<unsigned>(m)) / d;
+}
+
+CONSTCD11 inline month_day operator/(const day& d, int m) NOEXCEPT {return m / d;}
+
+// month_day_last from operator/()
+
+CONSTCD11
+inline
+month_day_last
+operator/(const month& m, last_spec) NOEXCEPT
+{
+    return month_day_last{m};
+}
+
+CONSTCD11
+inline
+month_day_last
+operator/(last_spec, const month& m) NOEXCEPT
+{
+    return m/last;
+}
+
+CONSTCD11
+inline
+month_day_last
+operator/(int m, last_spec) NOEXCEPT
+{
+    return month(static_cast<unsigned>(m))/last;
+}
+
+CONSTCD11
+inline
+month_day_last
+operator/(last_spec, int m) NOEXCEPT
+{
+    return m/last;
+}
+
+// month_weekday from operator/()
+
+CONSTCD11
+inline
+month_weekday
+operator/(const month& m, const weekday_indexed& wdi) NOEXCEPT
+{
+    return {m, wdi};
+}
+
+CONSTCD11
+inline
+month_weekday
+operator/(const weekday_indexed& wdi, const month& m) NOEXCEPT
+{
+    return m / wdi;
+}
+
+CONSTCD11
+inline
+month_weekday
+operator/(int m, const weekday_indexed& wdi) NOEXCEPT
+{
+    return month(static_cast<unsigned>(m)) / wdi;
+}
+
+CONSTCD11
+inline
+month_weekday
+operator/(const weekday_indexed& wdi, int m) NOEXCEPT
+{
+    return m / wdi;
+}
+
+// month_weekday_last from operator/()
+
+CONSTCD11
+inline
+month_weekday_last
+operator/(const month& m, const weekday_last& wdl) NOEXCEPT
+{
+    return {m, wdl};
+}
+
+CONSTCD11
+inline
+month_weekday_last
+operator/(const weekday_last& wdl, const month& m) NOEXCEPT
+{
+    return m / wdl;
+}
+
+CONSTCD11
+inline
+month_weekday_last
+operator/(int m, const weekday_last& wdl) NOEXCEPT
+{
+    return month(static_cast<unsigned>(m)) / wdl;
+}
+
+CONSTCD11
+inline
+month_weekday_last
+operator/(const weekday_last& wdl, int m) NOEXCEPT
+{
+    return m / wdl;
+}
+
+// year_month_day from operator/()
+
+CONSTCD11
+inline
+year_month_day
+operator/(const year_month& ym, const day& d) NOEXCEPT
+{
+    return {ym.year(), ym.month(), d};
+}
+
+CONSTCD11
+inline
+year_month_day
+operator/(const year_month& ym, int d)  NOEXCEPT
+{
+    return ym / day(static_cast<unsigned>(d));
+}
+
+CONSTCD11
+inline
+year_month_day
+operator/(const year& y, const month_day& md) NOEXCEPT
+{
+    return y / md.month() / md.day();
+}
+
+CONSTCD11
+inline
+year_month_day
+operator/(int y, const month_day& md) NOEXCEPT
+{
+    return year(y) / md;
+}
+
+CONSTCD11
+inline
+year_month_day
+operator/(const month_day& md, const year& y)  NOEXCEPT
+{
+    return y / md;
+}
+
+CONSTCD11
+inline
+year_month_day
+operator/(const month_day& md, int y) NOEXCEPT
+{
+    return year(y) / md;
+}
+
+// year_month_day_last from operator/()
+
+CONSTCD11
+inline
+year_month_day_last
+operator/(const year_month& ym, last_spec) NOEXCEPT
+{
+    return {ym.year(), month_day_last{ym.month()}};
+}
+
+CONSTCD11
+inline
+year_month_day_last
+operator/(const year& y, const month_day_last& mdl) NOEXCEPT
+{
+    return {y, mdl};
+}
+
+CONSTCD11
+inline
+year_month_day_last
+operator/(int y, const month_day_last& mdl) NOEXCEPT
+{
+    return year(y) / mdl;
+}
+
+CONSTCD11
+inline
+year_month_day_last
+operator/(const month_day_last& mdl, const year& y) NOEXCEPT
+{
+    return y / mdl;
+}
+
+CONSTCD11
+inline
+year_month_day_last
+operator/(const month_day_last& mdl, int y) NOEXCEPT
+{
+    return year(y) / mdl;
+}
+
+// year_month_weekday from operator/()
+
+CONSTCD11
+inline
+year_month_weekday
+operator/(const year_month& ym, const weekday_indexed& wdi) NOEXCEPT
+{
+    return {ym.year(), ym.month(), wdi};
+}
+
+CONSTCD11
+inline
+year_month_weekday
+operator/(const year& y, const month_weekday& mwd) NOEXCEPT
+{
+    return {y, mwd.month(), mwd.weekday_indexed()};
+}
+
+CONSTCD11
+inline
+year_month_weekday
+operator/(int y, const month_weekday& mwd) NOEXCEPT
+{
+    return year(y) / mwd;
+}
+
+CONSTCD11
+inline
+year_month_weekday
+operator/(const month_weekday& mwd, const year& y) NOEXCEPT
+{
+    return y / mwd;
+}
+
+CONSTCD11
+inline
+year_month_weekday
+operator/(const month_weekday& mwd, int y) NOEXCEPT
+{
+    return year(y) / mwd;
+}
+
+// year_month_weekday_last from operator/()
+
+CONSTCD11
+inline
+year_month_weekday_last
+operator/(const year_month& ym, const weekday_last& wdl) NOEXCEPT
+{
+    return {ym.year(), ym.month(), wdl};
+}
+
+CONSTCD11
+inline
+year_month_weekday_last
+operator/(const year& y, const month_weekday_last& mwdl) NOEXCEPT
+{
+    return {y, mwdl.month(), mwdl.weekday_last()};
+}
+
+CONSTCD11
+inline
+year_month_weekday_last
+operator/(int y, const month_weekday_last& mwdl) NOEXCEPT
+{
+    return year(y) / mwdl;
+}
+
+CONSTCD11
+inline
+year_month_weekday_last
+operator/(const month_weekday_last& mwdl, const year& y) NOEXCEPT
+{
+    return y / mwdl;
+}
+
+CONSTCD11
+inline
+year_month_weekday_last
+operator/(const month_weekday_last& mwdl, int y) NOEXCEPT
+{
+    return year(y) / mwdl;
+}
+
+}  // namespace solar_hijri
+
+#endif  // SOLAR_HIJRI_H
diff --git a/third_party/date-3.0.1/include/date/tz.h b/third_party/date-3.0.1/include/date/tz.h
new file mode 100644
index 00000000..49210683
--- /dev/null
+++ b/third_party/date-3.0.1/include/date/tz.h
@@ -0,0 +1,2792 @@
+#ifndef TZ_H
+#define TZ_H
+
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016, 2017 Howard Hinnant
+// Copyright (c) 2017 Jiangang Zhuang
+// Copyright (c) 2017 Aaron Bishop
+// Copyright (c) 2017 Tomasz Kamiński
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+//
+// Our apologies.  When the previous paragraph was written, lowercase had not yet
+// been invented (that would involve another several millennia of evolution).
+// We did not mean to shout.
+
+// Get more recent database at http://www.iana.org/time-zones
+
+// The notion of "current timezone" is something the operating system is expected to "just
+// know". How it knows this is system specific. It's often a value set by the user at OS
+// installation time and recorded by the OS somewhere. On Linux and Mac systems the current
+// timezone name is obtained by looking at the name or contents of a particular file on
+// disk. On Windows the current timezone name comes from the registry. In either method,
+// there is no guarantee that the "native" current timezone name obtained will match any
+// of the "Standard" names in this library's "database". On Linux, the names usually do
+// seem to match so mapping functions to map from native to "Standard" are typically not
+// required. On Windows, the names are never "Standard" so mapping is always required.
+// Technically any OS may use the mapping process but currently only Windows does use it.
+
+#ifndef USE_OS_TZDB
+#  define USE_OS_TZDB 0
+#endif
+
+#ifndef HAS_REMOTE_API
+#  if USE_OS_TZDB == 0
+#    ifdef _WIN32
+#      define HAS_REMOTE_API 0
+#    else
+#      define HAS_REMOTE_API 1
+#    endif
+#  else  // HAS_REMOTE_API makes no since when using the OS timezone database
+#    define HAS_REMOTE_API 0
+#  endif
+#endif
+
+#ifdef __clang__
+# pragma clang diagnostic push
+# pragma clang diagnostic ignored "-Wconstant-logical-operand"
+#endif
+
+static_assert(!(USE_OS_TZDB && HAS_REMOTE_API),
+              "USE_OS_TZDB and HAS_REMOTE_API can not be used together");
+
+#ifdef __clang__
+# pragma clang diagnostic pop
+#endif
+
+#ifndef AUTO_DOWNLOAD
+#  define AUTO_DOWNLOAD HAS_REMOTE_API
+#endif
+
+static_assert(HAS_REMOTE_API == 0 ? AUTO_DOWNLOAD == 0 : true,
+              "AUTO_DOWNLOAD can not be turned on without HAS_REMOTE_API");
+
+#ifndef USE_SHELL_API
+#  define USE_SHELL_API 1
+#endif
+
+#if USE_OS_TZDB
+#  ifdef _WIN32
+#    error "USE_OS_TZDB can not be used on Windows"
+#  endif
+#endif
+
+#ifndef HAS_DEDUCTION_GUIDES
+#  if __cplusplus >= 201703
+#    define HAS_DEDUCTION_GUIDES 1
+#  else
+#    define HAS_DEDUCTION_GUIDES 0
+#  endif
+#endif  // HAS_DEDUCTION_GUIDES
+
+#include "date.h"
+
+#if defined(_MSC_VER) && (_MSC_VER < 1900)
+#include "tz_private.h"
+#endif
+
+#include <algorithm>
+#include <atomic>
+#include <cassert>
+#include <chrono>
+#include <istream>
+#include <locale>
+#include <memory>
+#include <mutex>
+#include <ostream>
+#include <sstream>
+#include <stdexcept>
+#include <string>
+#include <type_traits>
+#include <utility>
+#include <vector>
+
+#ifdef _WIN32
+#  ifdef DATE_BUILD_DLL
+#    define DATE_API __declspec(dllexport)
+#  elif defined(DATE_USE_DLL)
+#    define DATE_API __declspec(dllimport)
+#  else
+#    define DATE_API
+#  endif
+#else
+#  ifdef DATE_BUILD_DLL
+#    define DATE_API __attribute__ ((visibility ("default")))
+#  else
+#    define DATE_API
+#  endif
+#endif
+
+namespace date
+{
+
+enum class choose {earliest, latest};
+
+namespace detail
+{
+    struct undocumented;
+
+    template<typename T>
+    struct nodeduct
+    {
+       using type = T;
+    };
+
+    template<typename T>
+    using nodeduct_t = typename nodeduct<T>::type;
+}
+
+struct sys_info
+{
+    sys_seconds          begin;
+    sys_seconds          end;
+    std::chrono::seconds offset;
+    std::chrono::minutes save;
+    std::string          abbrev;
+};
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const sys_info& r)
+{
+    os << r.begin << '\n';
+    os << r.end << '\n';
+    os << make_time(r.offset) << "\n";
+    os << make_time(r.save) << "\n";
+    os << r.abbrev << '\n';
+    return os;
+}
+
+struct local_info
+{
+    enum {unique, nonexistent, ambiguous} result;
+    sys_info first;
+    sys_info second;
+};
+
+template<class CharT, class Traits>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const local_info& r)
+{
+    if (r.result == local_info::nonexistent)
+        os << "nonexistent between\n";
+    else if (r.result == local_info::ambiguous)
+        os << "ambiguous between\n";
+    os << r.first;
+    if (r.result != local_info::unique)
+    {
+        os << "and\n";
+        os << r.second;
+    }
+    return os;
+}
+
+class nonexistent_local_time
+    : public std::runtime_error
+{
+public:
+    template <class Duration>
+        nonexistent_local_time(local_time<Duration> tp, const local_info& i);
+
+private:
+    template <class Duration>
+    static
+    std::string
+    make_msg(local_time<Duration> tp, const local_info& i);
+};
+
+template <class Duration>
+inline
+nonexistent_local_time::nonexistent_local_time(local_time<Duration> tp,
+                                               const local_info& i)
+    : std::runtime_error(make_msg(tp, i))
+{
+}
+
+template <class Duration>
+std::string
+nonexistent_local_time::make_msg(local_time<Duration> tp, const local_info& i)
+{
+    assert(i.result == local_info::nonexistent);
+    std::ostringstream os;
+    os << tp << " is in a gap between\n"
+       << local_seconds{i.first.end.time_since_epoch()} + i.first.offset << ' '
+       << i.first.abbrev << " and\n"
+       << local_seconds{i.second.begin.time_since_epoch()} + i.second.offset << ' '
+       << i.second.abbrev
+       << " which are both equivalent to\n"
+       << i.first.end << " UTC";
+    return os.str();
+}
+
+class ambiguous_local_time
+    : public std::runtime_error
+{
+public:
+    template <class Duration>
+        ambiguous_local_time(local_time<Duration> tp, const local_info& i);
+
+private:
+    template <class Duration>
+    static
+    std::string
+    make_msg(local_time<Duration> tp, const local_info& i);
+};
+
+template <class Duration>
+inline
+ambiguous_local_time::ambiguous_local_time(local_time<Duration> tp, const local_info& i)
+    : std::runtime_error(make_msg(tp, i))
+{
+}
+
+template <class Duration>
+std::string
+ambiguous_local_time::make_msg(local_time<Duration> tp, const local_info& i)
+{
+    assert(i.result == local_info::ambiguous);
+    std::ostringstream os;
+    os << tp << " is ambiguous.  It could be\n"
+       << tp << ' ' << i.first.abbrev << " == "
+       << tp - i.first.offset << " UTC or\n"
+       << tp << ' ' << i.second.abbrev  << " == "
+       << tp - i.second.offset  << " UTC";
+    return os.str();
+}
+
+class time_zone;
+
+#if HAS_STRING_VIEW
+DATE_API const time_zone* locate_zone(std::string_view tz_name);
+#else
+DATE_API const time_zone* locate_zone(const std::string& tz_name);
+#endif
+
+DATE_API const time_zone* current_zone();
+
+template <class T>
+struct zoned_traits
+{
+};
+
+template <>
+struct zoned_traits<const time_zone*>
+{
+    static
+    const time_zone*
+    default_zone()
+    {
+        return date::locate_zone("Etc/UTC");
+    }
+
+#if HAS_STRING_VIEW
+
+    static
+    const time_zone*
+    locate_zone(std::string_view name)
+    {
+        return date::locate_zone(name);
+    }
+
+#else  // !HAS_STRING_VIEW
+
+    static
+    const time_zone*
+    locate_zone(const std::string& name)
+    {
+        return date::locate_zone(name);
+    }
+
+    static
+    const time_zone*
+    locate_zone(const char* name)
+    {
+        return date::locate_zone(name);
+    }
+
+#endif  // !HAS_STRING_VIEW
+};
+
+template <class Duration, class TimeZonePtr>
+class zoned_time;
+
+template <class Duration1, class Duration2, class TimeZonePtr>
+bool
+operator==(const zoned_time<Duration1, TimeZonePtr>& x,
+           const zoned_time<Duration2, TimeZonePtr>& y);
+
+template <class Duration, class TimeZonePtr = const time_zone*>
+class zoned_time
+{
+public:
+    using duration = typename std::common_type<Duration, std::chrono::seconds>::type;
+
+private:
+    TimeZonePtr        zone_;
+    sys_time<duration> tp_;
+
+public:
+#if !defined(_MSC_VER) || (_MSC_VER > 1916)
+    template <class T = TimeZonePtr,
+              class = decltype(zoned_traits<T>::default_zone())>
+#endif
+        zoned_time();
+
+#if !defined(_MSC_VER) || (_MSC_VER > 1916)
+    template <class T = TimeZonePtr,
+              class = decltype(zoned_traits<T>::default_zone())>
+#endif
+        zoned_time(const sys_time<Duration>& st);
+    explicit zoned_time(TimeZonePtr z);
+
+#if HAS_STRING_VIEW
+    template <class T = TimeZonePtr,
+              class = typename std::enable_if
+              <
+                  std::is_constructible
+                  <
+                      zoned_time,
+                      decltype(zoned_traits<T>::locate_zone(std::string_view()))
+                  >::value
+              >::type>
+        explicit zoned_time(std::string_view name);
+#else
+#  if !defined(_MSC_VER) || (_MSC_VER > 1916)
+    template <class T = TimeZonePtr,
+              class = typename std::enable_if
+              <
+                  std::is_constructible
+                  <
+                      zoned_time,
+                      decltype(zoned_traits<T>::locate_zone(std::string()))
+                  >::value
+              >::type>
+#  endif
+        explicit zoned_time(const std::string& name);
+#endif
+
+    template <class Duration2,
+              class = typename std::enable_if
+                      <
+                          std::is_convertible<sys_time<Duration2>,
+                                              sys_time<Duration>>::value
+                      >::type>
+        zoned_time(const zoned_time<Duration2, TimeZonePtr>& zt) NOEXCEPT;
+
+    zoned_time(TimeZonePtr z, const sys_time<Duration>& st);
+
+#if !defined(_MSC_VER) || (_MSC_VER > 1916)
+    template <class T = TimeZonePtr,
+              class = typename std::enable_if
+              <
+                  std::is_convertible
+                  <
+                      decltype(std::declval<T&>()->to_sys(local_time<Duration>{})),
+                      sys_time<duration>
+                  >::value
+              >::type>
+#endif
+        zoned_time(TimeZonePtr z, const local_time<Duration>& tp);
+
+#if !defined(_MSC_VER) || (_MSC_VER > 1916)
+    template <class T = TimeZonePtr,
+              class = typename std::enable_if
+              <
+                  std::is_convertible
+                  <
+                      decltype(std::declval<T&>()->to_sys(local_time<Duration>{},
+                                                          choose::earliest)),
+                      sys_time<duration>
+                  >::value
+              >::type>
+#endif
+        zoned_time(TimeZonePtr z, const local_time<Duration>& tp, choose c);
+
+    template <class Duration2, class TimeZonePtr2,
+              class = typename std::enable_if
+                      <
+                          std::is_convertible<sys_time<Duration2>,
+                                              sys_time<Duration>>::value
+                      >::type>
+        zoned_time(TimeZonePtr z, const zoned_time<Duration2, TimeZonePtr2>& zt);
+
+    template <class Duration2, class TimeZonePtr2,
+              class = typename std::enable_if
+                      <
+                          std::is_convertible<sys_time<Duration2>,
+                                              sys_time<Duration>>::value
+                      >::type>
+        zoned_time(TimeZonePtr z, const zoned_time<Duration2, TimeZonePtr2>& zt, choose);
+
+#if HAS_STRING_VIEW
+
+    template <class T = TimeZonePtr,
+              class = typename std::enable_if
+              <
+                  std::is_constructible
+                  <
+                      zoned_time,
+                      decltype(zoned_traits<T>::locate_zone(std::string_view())),
+                      sys_time<Duration>
+                  >::value
+              >::type>
+        zoned_time(std::string_view name, detail::nodeduct_t<const sys_time<Duration>&> st);
+
+    template <class T = TimeZonePtr,
+              class = typename std::enable_if
+              <
+                  std::is_constructible
+                  <
+                      zoned_time,
+                      decltype(zoned_traits<T>::locate_zone(std::string_view())),
+                      local_time<Duration>
+                  >::value
+              >::type>
+        zoned_time(std::string_view name, detail::nodeduct_t<const local_time<Duration>&> tp);
+
+    template <class T = TimeZonePtr,
+              class = typename std::enable_if
+              <
+                  std::is_constructible
+                  <
+                      zoned_time,
+                      decltype(zoned_traits<T>::locate_zone(std::string_view())),
+                      local_time<Duration>,
+                      choose
+                  >::value
+              >::type>
+        zoned_time(std::string_view name, detail::nodeduct_t<const local_time<Duration>&> tp, choose c);
+
+    template <class Duration2, class TimeZonePtr2, class T = TimeZonePtr,
+              class = typename std::enable_if
+                      <
+                          std::is_convertible<sys_time<Duration2>,
+                                              sys_time<Duration>>::value &&
+                          std::is_constructible
+                          <
+                              zoned_time,
+                              decltype(zoned_traits<T>::locate_zone(std::string_view())),
+                              zoned_time
+                          >::value
+                      >::type>
+        zoned_time(std::string_view name, const zoned_time<Duration2, TimeZonePtr2>& zt);
+
+    template <class Duration2, class TimeZonePtr2, class T = TimeZonePtr,
+              class = typename std::enable_if
+                      <
+                          std::is_convertible<sys_time<Duration2>,
+                                              sys_time<Duration>>::value &&
+                          std::is_constructible
+                          <
+                              zoned_time,
+                              decltype(zoned_traits<T>::locate_zone(std::string_view())),
+                              zoned_time,
+                              choose
+                          >::value
+                      >::type>
+        zoned_time(std::string_view name, const zoned_time<Duration2, TimeZonePtr2>& zt, choose);
+
+#else  // !HAS_STRING_VIEW
+
+#if !defined(_MSC_VER) || (_MSC_VER > 1916)
+    template <class T = TimeZonePtr,
+              class = typename std::enable_if
+              <
+                  std::is_constructible
+                  <
+                      zoned_time,
+                      decltype(zoned_traits<T>::locate_zone(std::string())),
+                      sys_time<Duration>
+                  >::value
+              >::type>
+#endif
+        zoned_time(const std::string& name, const sys_time<Duration>& st);
+
+#if !defined(_MSC_VER) || (_MSC_VER > 1916)
+    template <class T = TimeZonePtr,
+              class = typename std::enable_if
+              <
+                  std::is_constructible
+                  <
+                      zoned_time,
+                      decltype(zoned_traits<T>::locate_zone(std::string())),
+                      sys_time<Duration>
+                  >::value
+              >::type>
+#endif
+        zoned_time(const char* name, const sys_time<Duration>& st);
+
+#if !defined(_MSC_VER) || (_MSC_VER > 1916)
+    template <class T = TimeZonePtr,
+              class = typename std::enable_if
+              <
+                  std::is_constructible
+                  <
+                      zoned_time,
+                      decltype(zoned_traits<T>::locate_zone(std::string())),
+                      local_time<Duration>
+                  >::value
+              >::type>
+#endif
+        zoned_time(const std::string& name, const local_time<Duration>& tp);
+
+#if !defined(_MSC_VER) || (_MSC_VER > 1916)
+    template <class T = TimeZonePtr,
+              class = typename std::enable_if
+              <
+                  std::is_constructible
+                  <
+                      zoned_time,
+                      decltype(zoned_traits<T>::locate_zone(std::string())),
+                      local_time<Duration>
+                  >::value
+              >::type>
+#endif
+        zoned_time(const char* name, const local_time<Duration>& tp);
+
+#if !defined(_MSC_VER) || (_MSC_VER > 1916)
+    template <class T = TimeZonePtr,
+              class = typename std::enable_if
+              <
+                  std::is_constructible
+                  <
+                      zoned_time,
+                      decltype(zoned_traits<T>::locate_zone(std::string())),
+                      local_time<Duration>,
+                      choose
+                  >::value
+              >::type>
+#endif
+        zoned_time(const std::string& name, const local_time<Duration>& tp, choose c);
+
+#if !defined(_MSC_VER) || (_MSC_VER > 1916)
+    template <class T = TimeZonePtr,
+              class = typename std::enable_if
+              <
+                  std::is_constructible
+                  <
+                      zoned_time,
+                      decltype(zoned_traits<T>::locate_zone(std::string())),
+                      local_time<Duration>,
+                      choose
+                  >::value
+              >::type>
+#endif
+        zoned_time(const char* name, const local_time<Duration>& tp, choose c);
+
+#if !defined(_MSC_VER) || (_MSC_VER > 1916)
+    template <class Duration2, class TimeZonePtr2, class T = TimeZonePtr,
+              class = typename std::enable_if
+                      <
+                          std::is_convertible<sys_time<Duration2>,
+                                              sys_time<Duration>>::value &&
+                          std::is_constructible
+                          <
+                              zoned_time,
+                              decltype(zoned_traits<T>::locate_zone(std::string())),
+                              zoned_time
+                          >::value
+                      >::type>
+#else
+    template <class Duration2, class TimeZonePtr2>
+#endif
+        zoned_time(const std::string& name, const zoned_time<Duration2, TimeZonePtr2>& zt);
+
+#if !defined(_MSC_VER) || (_MSC_VER > 1916)
+    template <class Duration2, class TimeZonePtr2, class T = TimeZonePtr,
+              class = typename std::enable_if
+                      <
+                          std::is_convertible<sys_time<Duration2>,
+                                              sys_time<Duration>>::value &&
+                          std::is_constructible
+                          <
+                              zoned_time,
+                              decltype(zoned_traits<T>::locate_zone(std::string())),
+                              zoned_time
+                          >::value
+                      >::type>
+#else
+    template <class Duration2, class TimeZonePtr2>
+#endif
+        zoned_time(const char* name, const zoned_time<Duration2, TimeZonePtr2>& zt);
+
+#if !defined(_MSC_VER) || (_MSC_VER > 1916)
+    template <class Duration2, class TimeZonePtr2, class T = TimeZonePtr,
+              class = typename std::enable_if
+                      <
+                          std::is_convertible<sys_time<Duration2>,
+                                              sys_time<Duration>>::value &&
+                          std::is_constructible
+                          <
+                              zoned_time,
+                              decltype(zoned_traits<T>::locate_zone(std::string())),
+                              zoned_time,
+                              choose
+                          >::value
+                      >::type>
+#else
+    template <class Duration2, class TimeZonePtr2>
+#endif
+        zoned_time(const std::string& name, const zoned_time<Duration2, TimeZonePtr2>& zt,
+                   choose);
+
+#if !defined(_MSC_VER) || (_MSC_VER > 1916)
+    template <class Duration2, class TimeZonePtr2, class T = TimeZonePtr,
+              class = typename std::enable_if
+                      <
+                          std::is_convertible<sys_time<Duration2>,
+                                              sys_time<Duration>>::value &&
+                          std::is_constructible
+                          <
+                              zoned_time,
+                              decltype(zoned_traits<T>::locate_zone(std::string())),
+                              zoned_time,
+                              choose
+                          >::value
+                      >::type>
+#else
+    template <class Duration2, class TimeZonePtr2>
+#endif
+        zoned_time(const char* name, const zoned_time<Duration2, TimeZonePtr2>& zt,
+                   choose);
+
+#endif  // !HAS_STRING_VIEW
+
+    zoned_time& operator=(const sys_time<Duration>& st);
+    zoned_time& operator=(const local_time<Duration>& ut);
+
+    explicit operator sys_time<duration>() const;
+    explicit operator local_time<duration>() const;
+
+    TimeZonePtr          get_time_zone() const;
+    local_time<duration> get_local_time() const;
+    sys_time<duration>   get_sys_time() const;
+    sys_info             get_info() const;
+
+    template <class Duration1, class Duration2, class TimeZonePtr1>
+    friend
+    bool
+    operator==(const zoned_time<Duration1, TimeZonePtr1>& x,
+               const zoned_time<Duration2, TimeZonePtr1>& y);
+
+    template <class CharT, class Traits, class Duration1, class TimeZonePtr1>
+    friend
+    std::basic_ostream<CharT, Traits>&
+    operator<<(std::basic_ostream<CharT, Traits>& os,
+               const zoned_time<Duration1, TimeZonePtr1>& t);
+
+private:
+    template <class D, class T> friend class zoned_time;
+
+    template <class TimeZonePtr2>
+    static
+    TimeZonePtr2&&
+    check(TimeZonePtr2&& p);
+};
+
+using zoned_seconds = zoned_time<std::chrono::seconds>;
+
+#if HAS_DEDUCTION_GUIDES
+
+namespace detail
+{
+   template<typename TimeZonePtrOrName>
+   using time_zone_representation =
+       std::conditional_t
+       <
+           std::is_convertible<TimeZonePtrOrName, std::string_view>::value,
+           time_zone const*,
+           std::remove_cv_t<std::remove_reference_t<TimeZonePtrOrName>>
+       >;
+}
+
+zoned_time()
+    -> zoned_time<std::chrono::seconds>;
+
+template <class Duration>
+zoned_time(sys_time<Duration>)
+    -> zoned_time<std::common_type_t<Duration, std::chrono::seconds>>;
+
+template <class TimeZonePtrOrName>
+zoned_time(TimeZonePtrOrName&&)
+    -> zoned_time<std::chrono::seconds, detail::time_zone_representation<TimeZonePtrOrName>>;
+
+template <class TimeZonePtrOrName, class Duration>
+zoned_time(TimeZonePtrOrName&&, sys_time<Duration>)
+    -> zoned_time<std::common_type_t<Duration, std::chrono::seconds>, detail::time_zone_representation<TimeZonePtrOrName>>;
+
+template <class TimeZonePtrOrName, class Duration>
+zoned_time(TimeZonePtrOrName&&, local_time<Duration>, choose = choose::earliest)
+    -> zoned_time<std::common_type_t<Duration, std::chrono::seconds>, detail::time_zone_representation<TimeZonePtrOrName>>;
+
+template <class Duration, class TimeZonePtrOrName, class TimeZonePtr2>
+zoned_time(TimeZonePtrOrName&&, zoned_time<Duration, TimeZonePtr2>, choose = choose::earliest)
+    -> zoned_time<std::common_type_t<Duration, std::chrono::seconds>, detail::time_zone_representation<TimeZonePtrOrName>>;
+
+#endif  // HAS_DEDUCTION_GUIDES
+
+template <class Duration1, class Duration2, class TimeZonePtr>
+inline
+bool
+operator==(const zoned_time<Duration1, TimeZonePtr>& x,
+           const zoned_time<Duration2, TimeZonePtr>& y)
+{
+    return x.zone_ == y.zone_ && x.tp_ == y.tp_;
+}
+
+template <class Duration1, class Duration2, class TimeZonePtr>
+inline
+bool
+operator!=(const zoned_time<Duration1, TimeZonePtr>& x,
+           const zoned_time<Duration2, TimeZonePtr>& y)
+{
+    return !(x == y);
+}
+
+#if !defined(_MSC_VER) || (_MSC_VER >= 1900)
+
+namespace detail
+{
+#  if USE_OS_TZDB
+    struct transition;
+    struct expanded_ttinfo;
+#  else  // !USE_OS_TZDB
+    struct zonelet;
+    class Rule;
+#  endif  // !USE_OS_TZDB
+}
+
+#endif  // !defined(_MSC_VER) || (_MSC_VER >= 1900)
+
+class time_zone
+{
+private:
+    std::string                          name_;
+#if USE_OS_TZDB
+    std::vector<detail::transition>      transitions_;
+    std::vector<detail::expanded_ttinfo> ttinfos_;
+#else  // !USE_OS_TZDB
+    std::vector<detail::zonelet>         zonelets_;
+#endif  // !USE_OS_TZDB
+    std::unique_ptr<std::once_flag>      adjusted_;
+
+public:
+#if !defined(_MSC_VER) || (_MSC_VER >= 1900)
+    time_zone(time_zone&&) = default;
+    time_zone& operator=(time_zone&&) = default;
+#else   // defined(_MSC_VER) && (_MSC_VER < 1900)
+    time_zone(time_zone&& src);
+    time_zone& operator=(time_zone&& src);
+#endif  // defined(_MSC_VER) && (_MSC_VER < 1900)
+
+    DATE_API explicit time_zone(const std::string& s, detail::undocumented);
+
+    const std::string& name() const NOEXCEPT;
+
+    template <class Duration> sys_info   get_info(sys_time<Duration> st) const;
+    template <class Duration> local_info get_info(local_time<Duration> tp) const;
+
+    template <class Duration>
+        sys_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+        to_sys(local_time<Duration> tp) const;
+
+    template <class Duration>
+        sys_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+        to_sys(local_time<Duration> tp, choose z) const;
+
+    template <class Duration>
+        local_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+        to_local(sys_time<Duration> tp) const;
+
+    friend bool operator==(const time_zone& x, const time_zone& y) NOEXCEPT;
+    friend bool operator< (const time_zone& x, const time_zone& y) NOEXCEPT;
+    friend DATE_API std::ostream& operator<<(std::ostream& os, const time_zone& z);
+
+#if !USE_OS_TZDB
+    DATE_API void add(const std::string& s);
+#endif  // !USE_OS_TZDB
+
+private:
+    DATE_API sys_info   get_info_impl(sys_seconds tp) const;
+    DATE_API local_info get_info_impl(local_seconds tp) const;
+
+    template <class Duration>
+        sys_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+        to_sys_impl(local_time<Duration> tp, choose z, std::false_type) const;
+    template <class Duration>
+        sys_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+        to_sys_impl(local_time<Duration> tp, choose, std::true_type) const;
+
+#if USE_OS_TZDB
+    DATE_API void init() const;
+    DATE_API void init_impl();
+    DATE_API sys_info
+        load_sys_info(std::vector<detail::transition>::const_iterator i) const;
+
+    template <class TimeType>
+    DATE_API void
+    load_data(std::istream& inf, std::int32_t tzh_leapcnt, std::int32_t tzh_timecnt,
+                                 std::int32_t tzh_typecnt, std::int32_t tzh_charcnt);
+#else  // !USE_OS_TZDB
+    DATE_API sys_info   get_info_impl(sys_seconds tp, int timezone) const;
+    DATE_API void adjust_infos(const std::vector<detail::Rule>& rules);
+    DATE_API void parse_info(std::istream& in);
+#endif  // !USE_OS_TZDB
+};
+
+#if defined(_MSC_VER) && (_MSC_VER < 1900)
+
+inline
+time_zone::time_zone(time_zone&& src)
+    : name_(std::move(src.name_))
+    , zonelets_(std::move(src.zonelets_))
+    , adjusted_(std::move(src.adjusted_))
+    {}
+
+inline
+time_zone&
+time_zone::operator=(time_zone&& src)
+{
+    name_ = std::move(src.name_);
+    zonelets_ = std::move(src.zonelets_);
+    adjusted_ = std::move(src.adjusted_);
+    return *this;
+}
+
+#endif  // defined(_MSC_VER) && (_MSC_VER < 1900)
+
+inline
+const std::string&
+time_zone::name() const NOEXCEPT
+{
+    return name_;
+}
+
+template <class Duration>
+inline
+sys_info
+time_zone::get_info(sys_time<Duration> st) const
+{
+    return get_info_impl(date::floor<std::chrono::seconds>(st));
+}
+
+template <class Duration>
+inline
+local_info
+time_zone::get_info(local_time<Duration> tp) const
+{
+    return get_info_impl(date::floor<std::chrono::seconds>(tp));
+}
+
+template <class Duration>
+inline
+sys_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+time_zone::to_sys(local_time<Duration> tp) const
+{
+    return to_sys_impl(tp, choose{}, std::true_type{});
+}
+
+template <class Duration>
+inline
+sys_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+time_zone::to_sys(local_time<Duration> tp, choose z) const
+{
+    return to_sys_impl(tp, z, std::false_type{});
+}
+
+template <class Duration>
+inline
+local_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+time_zone::to_local(sys_time<Duration> tp) const
+{
+    using LT = local_time<typename std::common_type<Duration, std::chrono::seconds>::type>;
+    auto i = get_info(tp);
+    return LT{(tp + i.offset).time_since_epoch()};
+}
+
+inline bool operator==(const time_zone& x, const time_zone& y) NOEXCEPT {return x.name_ == y.name_;}
+inline bool operator< (const time_zone& x, const time_zone& y) NOEXCEPT {return x.name_ < y.name_;}
+
+inline bool operator!=(const time_zone& x, const time_zone& y) NOEXCEPT {return !(x == y);}
+inline bool operator> (const time_zone& x, const time_zone& y) NOEXCEPT {return   y < x;}
+inline bool operator<=(const time_zone& x, const time_zone& y) NOEXCEPT {return !(y < x);}
+inline bool operator>=(const time_zone& x, const time_zone& y) NOEXCEPT {return !(x < y);}
+
+template <class Duration>
+sys_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+time_zone::to_sys_impl(local_time<Duration> tp, choose z, std::false_type) const
+{
+    auto i = get_info(tp);
+    if (i.result == local_info::nonexistent)
+    {
+        return i.first.end;
+    }
+    else if (i.result == local_info::ambiguous)
+    {
+        if (z == choose::latest)
+            return sys_time<Duration>{tp.time_since_epoch()} - i.second.offset;
+    }
+    return sys_time<Duration>{tp.time_since_epoch()} - i.first.offset;
+}
+
+template <class Duration>
+sys_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+time_zone::to_sys_impl(local_time<Duration> tp, choose, std::true_type) const
+{
+    auto i = get_info(tp);
+    if (i.result == local_info::nonexistent)
+        throw nonexistent_local_time(tp, i);
+    else if (i.result == local_info::ambiguous)
+        throw ambiguous_local_time(tp, i);
+    return sys_time<Duration>{tp.time_since_epoch()} - i.first.offset;
+}
+
+#if !USE_OS_TZDB
+
+class time_zone_link
+{
+private:
+    std::string name_;
+    std::string target_;
+public:
+    DATE_API explicit time_zone_link(const std::string& s);
+
+    const std::string& name() const {return name_;}
+    const std::string& target() const {return target_;}
+
+    friend bool operator==(const time_zone_link& x, const time_zone_link& y) {return x.name_ == y.name_;}
+    friend bool operator< (const time_zone_link& x, const time_zone_link& y) {return x.name_ < y.name_;}
+
+    friend DATE_API std::ostream& operator<<(std::ostream& os, const time_zone_link& x);
+};
+
+using link = time_zone_link;
+
+inline bool operator!=(const time_zone_link& x, const time_zone_link& y) {return !(x == y);}
+inline bool operator> (const time_zone_link& x, const time_zone_link& y) {return   y < x;}
+inline bool operator<=(const time_zone_link& x, const time_zone_link& y) {return !(y < x);}
+inline bool operator>=(const time_zone_link& x, const time_zone_link& y) {return !(x < y);}
+
+#endif  // !USE_OS_TZDB
+
+class leap_second
+{
+private:
+    sys_seconds date_;
+
+public:
+#if USE_OS_TZDB
+    DATE_API explicit leap_second(const sys_seconds& s, detail::undocumented);
+#else
+    DATE_API explicit leap_second(const std::string& s, detail::undocumented);
+#endif
+
+    sys_seconds date() const {return date_;}
+
+    friend bool operator==(const leap_second& x, const leap_second& y) {return x.date_ == y.date_;}
+    friend bool operator< (const leap_second& x, const leap_second& y) {return x.date_ < y.date_;}
+
+    template <class Duration>
+    friend
+    bool
+    operator==(const leap_second& x, const sys_time<Duration>& y)
+    {
+        return x.date_ == y;
+    }
+
+    template <class Duration>
+    friend
+    bool
+    operator< (const leap_second& x, const sys_time<Duration>& y)
+    {
+        return x.date_ < y;
+    }
+
+    template <class Duration>
+    friend
+    bool
+    operator< (const sys_time<Duration>& x, const leap_second& y)
+    {
+        return x < y.date_;
+    }
+
+    friend DATE_API std::ostream& operator<<(std::ostream& os, const leap_second& x);
+};
+
+inline bool operator!=(const leap_second& x, const leap_second& y) {return !(x == y);}
+inline bool operator> (const leap_second& x, const leap_second& y) {return   y < x;}
+inline bool operator<=(const leap_second& x, const leap_second& y) {return !(y < x);}
+inline bool operator>=(const leap_second& x, const leap_second& y) {return !(x < y);}
+
+template <class Duration>
+inline
+bool
+operator==(const sys_time<Duration>& x, const leap_second& y)
+{
+    return y == x;
+}
+
+template <class Duration>
+inline
+bool
+operator!=(const leap_second& x, const sys_time<Duration>& y)
+{
+    return !(x == y);
+}
+
+template <class Duration>
+inline
+bool
+operator!=(const sys_time<Duration>& x, const leap_second& y)
+{
+    return !(x == y);
+}
+
+template <class Duration>
+inline
+bool
+operator> (const leap_second& x, const sys_time<Duration>& y)
+{
+    return y < x;
+}
+
+template <class Duration>
+inline
+bool
+operator> (const sys_time<Duration>& x, const leap_second& y)
+{
+    return y < x;
+}
+
+template <class Duration>
+inline
+bool
+operator<=(const leap_second& x, const sys_time<Duration>& y)
+{
+    return !(y < x);
+}
+
+template <class Duration>
+inline
+bool
+operator<=(const sys_time<Duration>& x, const leap_second& y)
+{
+    return !(y < x);
+}
+
+template <class Duration>
+inline
+bool
+operator>=(const leap_second& x, const sys_time<Duration>& y)
+{
+    return !(x < y);
+}
+
+template <class Duration>
+inline
+bool
+operator>=(const sys_time<Duration>& x, const leap_second& y)
+{
+    return !(x < y);
+}
+
+using leap = leap_second;
+
+#ifdef _WIN32
+
+namespace detail
+{
+
+// The time zone mapping is modelled after this data file:
+// http://unicode.org/repos/cldr/trunk/common/supplemental/windowsZones.xml
+// and the field names match the element names from the mapZone element
+// of windowsZones.xml.
+// The website displays this file here:
+// http://www.unicode.org/cldr/charts/latest/supplemental/zone_tzid.html
+// The html view is sorted before being displayed but is otherwise the same
+// There is a mapping between the os centric view (in this case windows)
+// the html displays uses and the generic view the xml file.
+// That mapping is this:
+// display column "windows" -> xml field "other".
+// display column "region"  -> xml field "territory".
+// display column "tzid"    -> xml field "type".
+// This structure uses the generic terminology because it could be
+// used to to support other os/native name conversions, not just windows,
+// and using the same generic names helps retain the connection to the
+// origin of the data that we are using.
+struct timezone_mapping
+{
+    timezone_mapping(const char* other, const char* territory, const char* type)
+        : other(other), territory(territory), type(type)
+    {
+    }
+    timezone_mapping() = default;
+    std::string other;
+    std::string territory;
+    std::string type;
+};
+
+}  // detail
+
+#endif  // _WIN32
+
+struct tzdb
+{
+    std::string                 version = "unknown";
+    std::vector<time_zone>      zones;
+#if !USE_OS_TZDB
+    std::vector<time_zone_link> links;
+#endif
+    std::vector<leap_second>    leap_seconds;
+#if !USE_OS_TZDB
+    std::vector<detail::Rule>   rules;
+#endif
+#ifdef _WIN32
+    std::vector<detail::timezone_mapping> mappings;
+#endif
+    tzdb* next = nullptr;
+
+    tzdb() = default;
+#if !defined(_MSC_VER) || (_MSC_VER >= 1900)
+    tzdb(tzdb&&) = default;
+    tzdb& operator=(tzdb&&) = default;
+#else  // defined(_MSC_VER) && (_MSC_VER < 1900)
+    tzdb(tzdb&& src)
+        : version(std::move(src.version))
+        , zones(std::move(src.zones))
+        , links(std::move(src.links))
+        , leap_seconds(std::move(src.leap_seconds))
+        , rules(std::move(src.rules))
+        , mappings(std::move(src.mappings))
+    {}
+
+    tzdb& operator=(tzdb&& src)
+    {
+        version = std::move(src.version);
+        zones = std::move(src.zones);
+        links = std::move(src.links);
+        leap_seconds = std::move(src.leap_seconds);
+        rules = std::move(src.rules);
+        mappings = std::move(src.mappings);
+        return *this;
+    }
+#endif  // defined(_MSC_VER) && (_MSC_VER < 1900)
+
+#if HAS_STRING_VIEW
+    const time_zone* locate_zone(std::string_view tz_name) const;
+#else
+    const time_zone* locate_zone(const std::string& tz_name) const;
+#endif
+    const time_zone* current_zone() const;
+};
+
+using TZ_DB = tzdb;
+
+DATE_API std::ostream&
+operator<<(std::ostream& os, const tzdb& db);
+
+DATE_API const tzdb& get_tzdb();
+
+class tzdb_list
+{
+    std::atomic<tzdb*> head_{nullptr};
+
+public:
+    ~tzdb_list();
+    tzdb_list() = default;
+    tzdb_list(tzdb_list&& x) NOEXCEPT;
+
+    const tzdb& front() const NOEXCEPT {return *head_;}
+          tzdb& front()       NOEXCEPT {return *head_;}
+
+    class const_iterator;
+
+    const_iterator begin() const NOEXCEPT;
+    const_iterator end() const NOEXCEPT;
+
+    const_iterator cbegin() const NOEXCEPT;
+    const_iterator cend() const NOEXCEPT;
+
+    const_iterator erase_after(const_iterator p) NOEXCEPT;
+
+    struct undocumented_helper;
+private:
+    void push_front(tzdb* tzdb) NOEXCEPT;
+};
+
+class tzdb_list::const_iterator
+{
+    tzdb* p_ = nullptr;
+
+    explicit const_iterator(tzdb* p) NOEXCEPT : p_{p} {}
+public:
+    const_iterator() = default;
+
+    using iterator_category = std::forward_iterator_tag;
+    using value_type        = tzdb;
+    using reference         = const value_type&;
+    using pointer           = const value_type*;
+    using difference_type   = std::ptrdiff_t;
+
+    reference operator*() const NOEXCEPT {return *p_;}
+    pointer  operator->() const NOEXCEPT {return p_;}
+
+    const_iterator& operator++() NOEXCEPT {p_ = p_->next; return *this;}
+    const_iterator  operator++(int) NOEXCEPT {auto t = *this; ++(*this); return t;}
+
+    friend
+    bool
+    operator==(const const_iterator& x, const const_iterator& y) NOEXCEPT
+        {return x.p_ == y.p_;}
+
+    friend
+    bool
+    operator!=(const const_iterator& x, const const_iterator& y) NOEXCEPT
+        {return !(x == y);}
+
+    friend class tzdb_list;
+};
+
+inline
+tzdb_list::const_iterator
+tzdb_list::begin() const NOEXCEPT
+{
+    return const_iterator{head_};
+}
+
+inline
+tzdb_list::const_iterator
+tzdb_list::end() const NOEXCEPT
+{
+    return const_iterator{nullptr};
+}
+
+inline
+tzdb_list::const_iterator
+tzdb_list::cbegin() const NOEXCEPT
+{
+    return begin();
+}
+
+inline
+tzdb_list::const_iterator
+tzdb_list::cend() const NOEXCEPT
+{
+    return end();
+}
+
+DATE_API tzdb_list& get_tzdb_list();
+
+#if !USE_OS_TZDB
+
+DATE_API const tzdb& reload_tzdb();
+DATE_API void        set_install(const std::string& install);
+
+#endif  // !USE_OS_TZDB
+
+#if HAS_REMOTE_API
+
+DATE_API std::string remote_version();
+// if provided error_buffer size should be at least CURL_ERROR_SIZE
+DATE_API bool        remote_download(const std::string& version, char* error_buffer = nullptr);
+DATE_API bool        remote_install(const std::string& version);
+
+#endif
+
+// zoned_time
+
+namespace detail
+{
+
+template <class T>
+inline
+T*
+to_raw_pointer(T* p) NOEXCEPT
+{
+    return p;
+}
+
+template <class Pointer>
+inline
+auto
+to_raw_pointer(Pointer p) NOEXCEPT
+    -> decltype(detail::to_raw_pointer(p.operator->()))
+{
+    return detail::to_raw_pointer(p.operator->());
+}
+
+}  // namespace detail
+
+template <class Duration, class TimeZonePtr>
+template <class TimeZonePtr2>
+inline
+TimeZonePtr2&&
+zoned_time<Duration, TimeZonePtr>::check(TimeZonePtr2&& p)
+{
+    if (detail::to_raw_pointer(p) == nullptr)
+        throw std::runtime_error(
+            "zoned_time constructed with a time zone pointer == nullptr");
+    return std::forward<TimeZonePtr2>(p);
+}
+
+template <class Duration, class TimeZonePtr>
+#if !defined(_MSC_VER) || (_MSC_VER > 1916)
+template <class T, class>
+#endif
+inline
+zoned_time<Duration, TimeZonePtr>::zoned_time()
+    : zone_(check(zoned_traits<TimeZonePtr>::default_zone()))
+    {}
+
+template <class Duration, class TimeZonePtr>
+#if !defined(_MSC_VER) || (_MSC_VER > 1916)
+template <class T, class>
+#endif
+inline
+zoned_time<Duration, TimeZonePtr>::zoned_time(const sys_time<Duration>& st)
+    : zone_(check(zoned_traits<TimeZonePtr>::default_zone()))
+    , tp_(st)
+    {}
+
+template <class Duration, class TimeZonePtr>
+inline
+zoned_time<Duration, TimeZonePtr>::zoned_time(TimeZonePtr z)
+    : zone_(check(std::move(z)))
+    {}
+
+#if HAS_STRING_VIEW
+
+template <class Duration, class TimeZonePtr>
+template <class T, class>
+inline
+zoned_time<Duration, TimeZonePtr>::zoned_time(std::string_view name)
+    : zoned_time(zoned_traits<TimeZonePtr>::locate_zone(name))
+    {}
+
+#else  // !HAS_STRING_VIEW
+
+template <class Duration, class TimeZonePtr>
+#if !defined(_MSC_VER) || (_MSC_VER > 1916)
+template <class T, class>
+#endif
+inline
+zoned_time<Duration, TimeZonePtr>::zoned_time(const std::string& name)
+    : zoned_time(zoned_traits<TimeZonePtr>::locate_zone(name))
+    {}
+
+#endif  // !HAS_STRING_VIEW
+
+template <class Duration, class TimeZonePtr>
+template <class Duration2, class>
+inline
+zoned_time<Duration, TimeZonePtr>::zoned_time(const zoned_time<Duration2, TimeZonePtr>& zt) NOEXCEPT
+    : zone_(zt.zone_)
+    , tp_(zt.tp_)
+    {}
+
+template <class Duration, class TimeZonePtr>
+inline
+zoned_time<Duration, TimeZonePtr>::zoned_time(TimeZonePtr z, const sys_time<Duration>& st)
+    : zone_(check(std::move(z)))
+    , tp_(st)
+    {}
+
+template <class Duration, class TimeZonePtr>
+#if !defined(_MSC_VER) || (_MSC_VER > 1916)
+template <class T, class>
+#endif
+inline
+zoned_time<Duration, TimeZonePtr>::zoned_time(TimeZonePtr z, const local_time<Duration>& t)
+    : zone_(check(std::move(z)))
+    , tp_(zone_->to_sys(t))
+    {}
+
+template <class Duration, class TimeZonePtr>
+#if !defined(_MSC_VER) || (_MSC_VER > 1916)
+template <class T, class>
+#endif
+inline
+zoned_time<Duration, TimeZonePtr>::zoned_time(TimeZonePtr z, const local_time<Duration>& t,
+                                              choose c)
+    : zone_(check(std::move(z)))
+    , tp_(zone_->to_sys(t, c))
+    {}
+
+template <class Duration, class TimeZonePtr>
+template <class Duration2, class TimeZonePtr2, class>
+inline
+zoned_time<Duration, TimeZonePtr>::zoned_time(TimeZonePtr z,
+                                              const zoned_time<Duration2, TimeZonePtr2>& zt)
+    : zone_(check(std::move(z)))
+    , tp_(zt.tp_)
+    {}
+
+template <class Duration, class TimeZonePtr>
+template <class Duration2, class TimeZonePtr2, class>
+inline
+zoned_time<Duration, TimeZonePtr>::zoned_time(TimeZonePtr z,
+                                      const zoned_time<Duration2, TimeZonePtr2>& zt, choose)
+    : zoned_time(std::move(z), zt)
+    {}
+
+#if HAS_STRING_VIEW
+
+template <class Duration, class TimeZonePtr>
+template <class T, class>
+inline
+zoned_time<Duration, TimeZonePtr>::zoned_time(std::string_view name,
+                                              detail::nodeduct_t<const sys_time<Duration>&> st)
+    : zoned_time(zoned_traits<TimeZonePtr>::locate_zone(name), st)
+    {}
+
+template <class Duration, class TimeZonePtr>
+template <class T, class>
+inline
+zoned_time<Duration, TimeZonePtr>::zoned_time(std::string_view name,
+                                              detail::nodeduct_t<const local_time<Duration>&> t)
+    : zoned_time(zoned_traits<TimeZonePtr>::locate_zone(name), t)
+    {}
+
+template <class Duration, class TimeZonePtr>
+template <class T, class>
+inline
+zoned_time<Duration, TimeZonePtr>::zoned_time(std::string_view name,
+                                              detail::nodeduct_t<const local_time<Duration>&> t, choose c)
+    : zoned_time(zoned_traits<TimeZonePtr>::locate_zone(name), t, c)
+    {}
+
+template <class Duration, class TimeZonePtr>
+template <class Duration2, class TimeZonePtr2, class, class>
+inline
+zoned_time<Duration, TimeZonePtr>::zoned_time(std::string_view name,
+                                              const zoned_time<Duration2, TimeZonePtr2>& zt)
+    : zoned_time(zoned_traits<TimeZonePtr>::locate_zone(name), zt)
+    {}
+
+template <class Duration, class TimeZonePtr>
+template <class Duration2, class TimeZonePtr2, class, class>
+inline
+zoned_time<Duration, TimeZonePtr>::zoned_time(std::string_view name,
+                                              const zoned_time<Duration2, TimeZonePtr2>& zt,
+                                              choose c)
+    : zoned_time(zoned_traits<TimeZonePtr>::locate_zone(name), zt, c)
+    {}
+
+#else  // !HAS_STRING_VIEW
+
+template <class Duration, class TimeZonePtr>
+#if !defined(_MSC_VER) || (_MSC_VER > 1916)
+template <class T, class>
+#endif
+inline
+zoned_time<Duration, TimeZonePtr>::zoned_time(const std::string& name,
+                                              const sys_time<Duration>& st)
+    : zoned_time(zoned_traits<TimeZonePtr>::locate_zone(name), st)
+    {}
+
+template <class Duration, class TimeZonePtr>
+#if !defined(_MSC_VER) || (_MSC_VER > 1916)
+template <class T, class>
+#endif
+inline
+zoned_time<Duration, TimeZonePtr>::zoned_time(const char* name,
+                                              const sys_time<Duration>& st)
+    : zoned_time(zoned_traits<TimeZonePtr>::locate_zone(name), st)
+    {}
+
+template <class Duration, class TimeZonePtr>
+#if !defined(_MSC_VER) || (_MSC_VER > 1916)
+template <class T, class>
+#endif
+inline
+zoned_time<Duration, TimeZonePtr>::zoned_time(const std::string& name,
+                                              const local_time<Duration>& t)
+    : zoned_time(zoned_traits<TimeZonePtr>::locate_zone(name), t)
+    {}
+
+template <class Duration, class TimeZonePtr>
+#if !defined(_MSC_VER) || (_MSC_VER > 1916)
+template <class T, class>
+#endif
+inline
+zoned_time<Duration, TimeZonePtr>::zoned_time(const char* name,
+                                              const local_time<Duration>& t)
+    : zoned_time(zoned_traits<TimeZonePtr>::locate_zone(name), t)
+    {}
+
+template <class Duration, class TimeZonePtr>
+#if !defined(_MSC_VER) || (_MSC_VER > 1916)
+template <class T, class>
+#endif
+inline
+zoned_time<Duration, TimeZonePtr>::zoned_time(const std::string& name,
+                                              const local_time<Duration>& t, choose c)
+    : zoned_time(zoned_traits<TimeZonePtr>::locate_zone(name), t, c)
+    {}
+
+template <class Duration, class TimeZonePtr>
+#if !defined(_MSC_VER) || (_MSC_VER > 1916)
+template <class T, class>
+#endif
+inline
+zoned_time<Duration, TimeZonePtr>::zoned_time(const char* name,
+                                              const local_time<Duration>& t, choose c)
+    : zoned_time(zoned_traits<TimeZonePtr>::locate_zone(name), t, c)
+    {}
+
+template <class Duration, class TimeZonePtr>
+#if !defined(_MSC_VER) || (_MSC_VER > 1916)
+template <class Duration2, class TimeZonePtr2, class, class>
+#else
+template <class Duration2, class TimeZonePtr2>
+#endif
+inline
+zoned_time<Duration, TimeZonePtr>::zoned_time(const std::string& name,
+                                              const zoned_time<Duration2, TimeZonePtr2>& zt)
+    : zoned_time(zoned_traits<TimeZonePtr>::locate_zone(name), zt)
+    {}
+
+template <class Duration, class TimeZonePtr>
+#if !defined(_MSC_VER) || (_MSC_VER > 1916)
+template <class Duration2, class TimeZonePtr2, class, class>
+#else
+template <class Duration2, class TimeZonePtr2>
+#endif
+inline
+zoned_time<Duration, TimeZonePtr>::zoned_time(const char* name,
+                                              const zoned_time<Duration2, TimeZonePtr2>& zt)
+    : zoned_time(zoned_traits<TimeZonePtr>::locate_zone(name), zt)
+    {}
+
+template <class Duration, class TimeZonePtr>
+#if !defined(_MSC_VER) || (_MSC_VER > 1916)
+template <class Duration2, class TimeZonePtr2, class, class>
+#else
+template <class Duration2, class TimeZonePtr2>
+#endif
+inline
+zoned_time<Duration, TimeZonePtr>::zoned_time(const std::string& name,
+                                              const zoned_time<Duration2, TimeZonePtr2>& zt,
+                                              choose c)
+    : zoned_time(zoned_traits<TimeZonePtr>::locate_zone(name), zt, c)
+    {}
+
+template <class Duration, class TimeZonePtr>
+#if !defined(_MSC_VER) || (_MSC_VER > 1916)
+template <class Duration2, class TimeZonePtr2, class, class>
+#else
+template <class Duration2, class TimeZonePtr2>
+#endif
+inline
+zoned_time<Duration, TimeZonePtr>::zoned_time(const char* name,
+                                              const zoned_time<Duration2, TimeZonePtr2>& zt,
+                                              choose c)
+    : zoned_time(zoned_traits<TimeZonePtr>::locate_zone(name), zt, c)
+    {}
+
+#endif  // HAS_STRING_VIEW
+
+template <class Duration, class TimeZonePtr>
+inline
+zoned_time<Duration, TimeZonePtr>&
+zoned_time<Duration, TimeZonePtr>::operator=(const sys_time<Duration>& st)
+{
+    tp_ = st;
+    return *this;
+}
+
+template <class Duration, class TimeZonePtr>
+inline
+zoned_time<Duration, TimeZonePtr>&
+zoned_time<Duration, TimeZonePtr>::operator=(const local_time<Duration>& ut)
+{
+    tp_ = zone_->to_sys(ut);
+    return *this;
+}
+
+template <class Duration, class TimeZonePtr>
+inline
+zoned_time<Duration, TimeZonePtr>::operator local_time<typename zoned_time<Duration, TimeZonePtr>::duration>() const
+{
+    return get_local_time();
+}
+
+template <class Duration, class TimeZonePtr>
+inline
+zoned_time<Duration, TimeZonePtr>::operator sys_time<typename zoned_time<Duration, TimeZonePtr>::duration>() const
+{
+    return get_sys_time();
+}
+
+template <class Duration, class TimeZonePtr>
+inline
+TimeZonePtr
+zoned_time<Duration, TimeZonePtr>::get_time_zone() const
+{
+    return zone_;
+}
+
+template <class Duration, class TimeZonePtr>
+inline
+local_time<typename zoned_time<Duration, TimeZonePtr>::duration>
+zoned_time<Duration, TimeZonePtr>::get_local_time() const
+{
+    return zone_->to_local(tp_);
+}
+
+template <class Duration, class TimeZonePtr>
+inline
+sys_time<typename zoned_time<Duration, TimeZonePtr>::duration>
+zoned_time<Duration, TimeZonePtr>::get_sys_time() const
+{
+    return tp_;
+}
+
+template <class Duration, class TimeZonePtr>
+inline
+sys_info
+zoned_time<Duration, TimeZonePtr>::get_info() const
+{
+    return zone_->get_info(tp_);
+}
+
+// make_zoned_time
+
+inline
+zoned_time<std::chrono::seconds>
+make_zoned()
+{
+    return zoned_time<std::chrono::seconds>();
+}
+
+template <class Duration>
+inline
+zoned_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+make_zoned(const sys_time<Duration>& tp)
+{
+    return zoned_time<typename std::common_type<Duration, std::chrono::seconds>::type>(tp);
+}
+
+template <class TimeZonePtr
+#if !defined(_MSC_VER) || (_MSC_VER > 1916)
+#if !defined(__INTEL_COMPILER) || (__INTEL_COMPILER > 1600)
+          , class = typename std::enable_if
+          <
+            std::is_class
+            <
+                typename std::decay
+                <
+                    decltype(*detail::to_raw_pointer(std::declval<TimeZonePtr&>()))
+                >::type
+            >{}
+          >::type
+#endif
+#endif
+         >
+inline
+zoned_time<std::chrono::seconds, TimeZonePtr>
+make_zoned(TimeZonePtr z)
+{
+    return zoned_time<std::chrono::seconds, TimeZonePtr>(std::move(z));
+}
+
+inline
+zoned_seconds
+make_zoned(const std::string& name)
+{
+    return zoned_seconds(name);
+}
+
+template <class Duration, class TimeZonePtr
+#if !defined(_MSC_VER) || (_MSC_VER > 1916)
+#if !defined(__INTEL_COMPILER) || (__INTEL_COMPILER > 1600)
+          , class = typename std::enable_if
+          <
+            std::is_class<typename std::decay<decltype(*std::declval<TimeZonePtr&>())>::type>{}
+          >::type
+#endif
+#endif
+         >
+inline
+zoned_time<typename std::common_type<Duration, std::chrono::seconds>::type, TimeZonePtr>
+make_zoned(TimeZonePtr zone, const local_time<Duration>& tp)
+{
+    return zoned_time<typename std::common_type<Duration, std::chrono::seconds>::type,
+                      TimeZonePtr>(std::move(zone), tp);
+}
+
+template <class Duration, class TimeZonePtr
+#if !defined(_MSC_VER) || (_MSC_VER > 1916)
+#if !defined(__INTEL_COMPILER) || (__INTEL_COMPILER > 1600)
+          , class = typename std::enable_if
+          <
+            std::is_class<typename std::decay<decltype(*std::declval<TimeZonePtr&>())>::type>{}
+          >::type
+#endif
+#endif
+         >
+inline
+zoned_time<typename std::common_type<Duration, std::chrono::seconds>::type, TimeZonePtr>
+make_zoned(TimeZonePtr zone, const local_time<Duration>& tp, choose c)
+{
+    return zoned_time<typename std::common_type<Duration, std::chrono::seconds>::type,
+                      TimeZonePtr>(std::move(zone), tp, c);
+}
+
+template <class Duration>
+inline
+zoned_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+make_zoned(const std::string& name, const local_time<Duration>& tp)
+{
+    return zoned_time<typename std::common_type<Duration,
+                      std::chrono::seconds>::type>(name, tp);
+}
+
+template <class Duration>
+inline
+zoned_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+make_zoned(const std::string& name, const local_time<Duration>& tp, choose c)
+{
+    return zoned_time<typename std::common_type<Duration,
+                      std::chrono::seconds>::type>(name, tp, c);
+}
+
+template <class Duration, class TimeZonePtr>
+inline
+zoned_time<Duration, TimeZonePtr>
+make_zoned(TimeZonePtr zone, const zoned_time<Duration, TimeZonePtr>& zt)
+{
+    return zoned_time<Duration, TimeZonePtr>(std::move(zone), zt);
+}
+
+template <class Duration, class TimeZonePtr>
+inline
+zoned_time<Duration, TimeZonePtr>
+make_zoned(const std::string& name, const zoned_time<Duration, TimeZonePtr>& zt)
+{
+    return zoned_time<Duration, TimeZonePtr>(name, zt);
+}
+
+template <class Duration, class TimeZonePtr>
+inline
+zoned_time<Duration, TimeZonePtr>
+make_zoned(TimeZonePtr zone, const zoned_time<Duration, TimeZonePtr>& zt, choose c)
+{
+    return zoned_time<Duration, TimeZonePtr>(std::move(zone), zt, c);
+}
+
+template <class Duration, class TimeZonePtr>
+inline
+zoned_time<Duration, TimeZonePtr>
+make_zoned(const std::string& name, const zoned_time<Duration, TimeZonePtr>& zt, choose c)
+{
+    return zoned_time<Duration, TimeZonePtr>(name, zt, c);
+}
+
+template <class Duration, class TimeZonePtr
+#if !defined(_MSC_VER) || (_MSC_VER > 1916)
+#if !defined(__INTEL_COMPILER) || (__INTEL_COMPILER > 1600)
+          , class = typename std::enable_if
+          <
+            std::is_class<typename std::decay<decltype(*std::declval<TimeZonePtr&>())>::type>{}
+          >::type
+#endif
+#endif
+         >
+inline
+zoned_time<typename std::common_type<Duration, std::chrono::seconds>::type, TimeZonePtr>
+make_zoned(TimeZonePtr zone, const sys_time<Duration>& st)
+{
+    return zoned_time<typename std::common_type<Duration, std::chrono::seconds>::type,
+                      TimeZonePtr>(std::move(zone), st);
+}
+
+template <class Duration>
+inline
+zoned_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+make_zoned(const std::string& name, const sys_time<Duration>& st)
+{
+    return zoned_time<typename std::common_type<Duration,
+                      std::chrono::seconds>::type>(name, st);
+}
+
+template <class CharT, class Traits, class Duration, class TimeZonePtr>
+std::basic_ostream<CharT, Traits>&
+to_stream(std::basic_ostream<CharT, Traits>& os, const CharT* fmt,
+          const zoned_time<Duration, TimeZonePtr>& tp)
+{
+    using duration = typename zoned_time<Duration, TimeZonePtr>::duration;
+    using LT = local_time<duration>;
+    auto const st = tp.get_sys_time();
+    auto const info = tp.get_time_zone()->get_info(st);
+    return to_stream(os, fmt, LT{(st+info.offset).time_since_epoch()},
+                     &info.abbrev, &info.offset);
+}
+
+template <class CharT, class Traits, class Duration, class TimeZonePtr>
+inline
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const zoned_time<Duration, TimeZonePtr>& t)
+{
+    const CharT fmt[] = {'%', 'F', ' ', '%', 'T', ' ', '%', 'Z', CharT{}};
+    return to_stream(os, fmt, t);
+}
+
+class utc_clock
+{
+public:
+    using duration                  = std::chrono::system_clock::duration;
+    using rep                       = duration::rep;
+    using period                    = duration::period;
+    using time_point                = std::chrono::time_point<utc_clock>;
+    static CONSTDATA bool is_steady = false;
+
+    static time_point now();
+
+    template<typename Duration>
+    static
+    std::chrono::time_point<std::chrono::system_clock, typename std::common_type<Duration, std::chrono::seconds>::type>
+    to_sys(const std::chrono::time_point<utc_clock, Duration>&);
+
+    template<typename Duration>
+    static
+    std::chrono::time_point<utc_clock, typename std::common_type<Duration, std::chrono::seconds>::type>
+    from_sys(const std::chrono::time_point<std::chrono::system_clock, Duration>&);
+
+    template<typename Duration>
+    static
+    std::chrono::time_point<local_t, typename std::common_type<Duration, std::chrono::seconds>::type>
+    to_local(const std::chrono::time_point<utc_clock, Duration>&);
+
+    template<typename Duration>
+    static
+    std::chrono::time_point<utc_clock, typename std::common_type<Duration, std::chrono::seconds>::type>
+    from_local(const std::chrono::time_point<local_t, Duration>&);
+};
+
+template <class Duration>
+    using utc_time = std::chrono::time_point<utc_clock, Duration>;
+
+using utc_seconds = utc_time<std::chrono::seconds>;
+
+template <class Duration>
+utc_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+utc_clock::from_sys(const sys_time<Duration>& st)
+{
+    using std::chrono::seconds;
+    using CD = typename std::common_type<Duration, seconds>::type;
+    auto const& leaps = get_tzdb().leap_seconds;
+    auto const lt = std::upper_bound(leaps.begin(), leaps.end(), st);
+    return utc_time<CD>{st.time_since_epoch() + seconds{lt-leaps.begin()}};
+}
+
+// Return pair<is_leap_second, seconds{number_of_leap_seconds_since_1970}>
+// first is true if ut is during a leap second insertion, otherwise false.
+// If ut is during a leap second insertion, that leap second is included in the count
+template <class Duration>
+std::pair<bool, std::chrono::seconds>
+is_leap_second(date::utc_time<Duration> const& ut)
+{
+    using std::chrono::seconds;
+    using duration = typename std::common_type<Duration, seconds>::type;
+    auto const& leaps = get_tzdb().leap_seconds;
+    auto tp = sys_time<duration>{ut.time_since_epoch()};
+    auto const lt = std::upper_bound(leaps.begin(), leaps.end(), tp);
+    auto ds = seconds{lt-leaps.begin()};
+    tp -= ds;
+    auto ls = false;
+    if (lt > leaps.begin())
+    {
+        if (tp < lt[-1])
+        {
+            if (tp >= lt[-1].date() - seconds{1})
+                ls = true;
+            else
+                --ds;
+        }
+    }
+    return {ls, ds};
+}
+
+struct leap_second_info
+{
+    bool is_leap_second;
+    std::chrono::seconds elapsed;
+};
+
+template <class Duration>
+leap_second_info
+get_leap_second_info(date::utc_time<Duration> const& ut)
+{
+    auto p = is_leap_second(ut);
+    return {p.first, p.second};
+}
+
+template <class Duration>
+sys_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+utc_clock::to_sys(const utc_time<Duration>& ut)
+{
+    using std::chrono::seconds;
+    using CD = typename std::common_type<Duration, seconds>::type;
+    auto ls = is_leap_second(ut);
+    auto tp = sys_time<CD>{ut.time_since_epoch() - ls.second};
+    if (ls.first)
+        tp = floor<seconds>(tp) + seconds{1} - CD{1};
+    return tp;
+}
+
+inline
+utc_clock::time_point
+utc_clock::now()
+{
+    return from_sys(std::chrono::system_clock::now());
+}
+
+template <class Duration>
+utc_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+utc_clock::from_local(const local_time<Duration>& st)
+{
+    return from_sys(sys_time<Duration>{st.time_since_epoch()});
+}
+
+template <class Duration>
+local_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+utc_clock::to_local(const utc_time<Duration>& ut)
+{
+    using CD = typename std::common_type<Duration, std::chrono::seconds>::type;
+    return local_time<CD>{to_sys(ut).time_since_epoch()};
+}
+
+template <class CharT, class Traits, class Duration>
+std::basic_ostream<CharT, Traits>&
+to_stream(std::basic_ostream<CharT, Traits>& os, const CharT* fmt,
+          const utc_time<Duration>& t)
+{
+    using std::chrono::seconds;
+    using CT = typename std::common_type<Duration, seconds>::type;
+    const std::string abbrev("UTC");
+    CONSTDATA seconds offset{0};
+    auto ls = is_leap_second(t);
+    auto tp = sys_time<CT>{t.time_since_epoch() - ls.second};
+    auto const sd = floor<days>(tp);
+    year_month_day ymd = sd;
+    auto time = make_time(tp - sys_seconds{sd});
+    time.seconds(detail::undocumented{}) += seconds{ls.first};
+    fields<CT> fds{ymd, time};
+    return to_stream(os, fmt, fds, &abbrev, &offset);
+}
+
+template <class CharT, class Traits, class Duration>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const utc_time<Duration>& t)
+{
+    const CharT fmt[] = {'%', 'F', ' ', '%', 'T', CharT{}};
+    return to_stream(os, fmt, t);
+}
+
+template <class Duration, class CharT, class Traits, class Alloc = std::allocator<CharT>>
+std::basic_istream<CharT, Traits>&
+from_stream(std::basic_istream<CharT, Traits>& is, const CharT* fmt,
+            utc_time<Duration>& tp, std::basic_string<CharT, Traits, Alloc>* abbrev = nullptr,
+            std::chrono::minutes* offset = nullptr)
+{
+    using std::chrono::seconds;
+    using std::chrono::minutes;
+    using CT = typename std::common_type<Duration, seconds>::type;
+    minutes offset_local{};
+    auto offptr = offset ? offset : &offset_local;
+    fields<CT> fds{};
+    fds.has_tod = true;
+    from_stream(is, fmt, fds, abbrev, offptr);
+    if (!fds.ymd.ok())
+        is.setstate(std::ios::failbit);
+    if (!is.fail())
+    {
+        bool is_60_sec = fds.tod.seconds() == seconds{60};
+        if (is_60_sec)
+            fds.tod.seconds(detail::undocumented{}) -= seconds{1};
+        auto tmp = utc_clock::from_sys(sys_days(fds.ymd) - *offptr + fds.tod.to_duration());
+        if (is_60_sec)
+            tmp += seconds{1};
+        if (is_60_sec != is_leap_second(tmp).first || !fds.tod.in_conventional_range())
+        {
+            is.setstate(std::ios::failbit);
+            return is;
+        }
+        tp = std::chrono::time_point_cast<Duration>(tmp);
+    }
+    return is;
+}
+
+// tai_clock
+
+class tai_clock
+{
+public:
+    using duration                  = std::chrono::system_clock::duration;
+    using rep                       = duration::rep;
+    using period                    = duration::period;
+    using time_point                = std::chrono::time_point<tai_clock>;
+    static const bool is_steady     = false;
+
+    static time_point now();
+
+    template<typename Duration>
+    static
+    std::chrono::time_point<utc_clock, typename std::common_type<Duration, std::chrono::seconds>::type>
+    to_utc(const std::chrono::time_point<tai_clock, Duration>&) NOEXCEPT;
+
+    template<typename Duration>
+    static
+    std::chrono::time_point<tai_clock, typename std::common_type<Duration, std::chrono::seconds>::type>
+    from_utc(const std::chrono::time_point<utc_clock, Duration>&) NOEXCEPT;
+
+    template<typename Duration>
+    static
+    std::chrono::time_point<local_t, typename std::common_type<Duration, date::days>::type>
+    to_local(const std::chrono::time_point<tai_clock, Duration>&) NOEXCEPT;
+
+    template<typename Duration>
+    static
+    std::chrono::time_point<tai_clock, typename std::common_type<Duration, date::days>::type>
+    from_local(const std::chrono::time_point<local_t, Duration>&) NOEXCEPT;
+};
+
+template <class Duration>
+    using tai_time = std::chrono::time_point<tai_clock, Duration>;
+
+using tai_seconds = tai_time<std::chrono::seconds>;
+
+template <class Duration>
+inline
+utc_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+tai_clock::to_utc(const tai_time<Duration>& t) NOEXCEPT
+{
+    using std::chrono::seconds;
+    using CD = typename std::common_type<Duration, seconds>::type;
+    return utc_time<CD>{t.time_since_epoch()} -
+            (sys_days(year{1970}/January/1) - sys_days(year{1958}/January/1) + seconds{10});
+}
+
+template <class Duration>
+inline
+tai_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+tai_clock::from_utc(const utc_time<Duration>& t) NOEXCEPT
+{
+    using std::chrono::seconds;
+    using CD = typename std::common_type<Duration, seconds>::type;
+    return tai_time<CD>{t.time_since_epoch()} +
+            (sys_days(year{1970}/January/1) - sys_days(year{1958}/January/1) + seconds{10});
+}
+
+inline
+tai_clock::time_point
+tai_clock::now()
+{
+    return from_utc(utc_clock::now());
+}
+
+template <class Duration>
+inline
+local_time<typename std::common_type<Duration, date::days>::type>
+tai_clock::to_local(const tai_time<Duration>& t) NOEXCEPT
+{
+    using CD = typename std::common_type<Duration, date::days>::type;
+    return local_time<CD>{t.time_since_epoch()} -
+           (local_days(year{1970}/January/1) - local_days(year{1958}/January/1));
+}
+
+template <class Duration>
+inline
+tai_time<typename std::common_type<Duration, date::days>::type>
+tai_clock::from_local(const local_time<Duration>& t) NOEXCEPT
+{
+    using CD = typename std::common_type<Duration, date::days>::type;
+    return tai_time<CD>{t.time_since_epoch()} +
+            (local_days(year{1970}/January/1) - local_days(year{1958}/January/1));
+}
+
+template <class CharT, class Traits, class Duration>
+std::basic_ostream<CharT, Traits>&
+to_stream(std::basic_ostream<CharT, Traits>& os, const CharT* fmt,
+          const tai_time<Duration>& t)
+{
+    const std::string abbrev("TAI");
+    CONSTDATA std::chrono::seconds offset{0};
+    return to_stream(os, fmt, tai_clock::to_local(t), &abbrev, &offset);
+}
+
+template <class CharT, class Traits, class Duration>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const tai_time<Duration>& t)
+{
+    const CharT fmt[] = {'%', 'F', ' ', '%', 'T', CharT{}};
+    return to_stream(os, fmt, t);
+}
+
+template <class Duration, class CharT, class Traits, class Alloc = std::allocator<CharT>>
+std::basic_istream<CharT, Traits>&
+from_stream(std::basic_istream<CharT, Traits>& is, const CharT* fmt,
+            tai_time<Duration>& tp,
+            std::basic_string<CharT, Traits, Alloc>* abbrev = nullptr,
+            std::chrono::minutes* offset = nullptr)
+{
+    local_time<Duration> lp;
+    from_stream(is, fmt, lp, abbrev, offset);
+    if (!is.fail())
+        tp = tai_clock::from_local(lp);
+    return is;
+}
+
+// gps_clock
+
+class gps_clock
+{
+public:
+    using duration                  = std::chrono::system_clock::duration;
+    using rep                       = duration::rep;
+    using period                    = duration::period;
+    using time_point                = std::chrono::time_point<gps_clock>;
+    static const bool is_steady     = false;
+
+    static time_point now();
+
+    template<typename Duration>
+    static
+    std::chrono::time_point<utc_clock, typename std::common_type<Duration, std::chrono::seconds>::type>
+    to_utc(const std::chrono::time_point<gps_clock, Duration>&) NOEXCEPT;
+
+    template<typename Duration>
+    static
+    std::chrono::time_point<gps_clock, typename std::common_type<Duration, std::chrono::seconds>::type>
+    from_utc(const std::chrono::time_point<utc_clock, Duration>&) NOEXCEPT;
+
+    template<typename Duration>
+    static
+    std::chrono::time_point<local_t, typename std::common_type<Duration, date::days>::type>
+    to_local(const std::chrono::time_point<gps_clock, Duration>&) NOEXCEPT;
+
+    template<typename Duration>
+    static
+    std::chrono::time_point<gps_clock, typename std::common_type<Duration, date::days>::type>
+    from_local(const std::chrono::time_point<local_t, Duration>&) NOEXCEPT;
+};
+
+template <class Duration>
+    using gps_time = std::chrono::time_point<gps_clock, Duration>;
+
+using gps_seconds = gps_time<std::chrono::seconds>;
+
+template <class Duration>
+inline
+utc_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+gps_clock::to_utc(const gps_time<Duration>& t) NOEXCEPT
+{
+    using std::chrono::seconds;
+    using CD = typename std::common_type<Duration, seconds>::type;
+    return utc_time<CD>{t.time_since_epoch()} +
+            (sys_days(year{1980}/January/Sunday[1]) - sys_days(year{1970}/January/1) +
+             seconds{9});
+}
+
+template <class Duration>
+inline
+gps_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+gps_clock::from_utc(const utc_time<Duration>& t) NOEXCEPT
+{
+    using std::chrono::seconds;
+    using CD = typename std::common_type<Duration, seconds>::type;
+    return gps_time<CD>{t.time_since_epoch()} -
+            (sys_days(year{1980}/January/Sunday[1]) - sys_days(year{1970}/January/1) +
+             seconds{9});
+}
+
+inline
+gps_clock::time_point
+gps_clock::now()
+{
+    return from_utc(utc_clock::now());
+}
+
+template <class Duration>
+inline
+local_time<typename std::common_type<Duration, date::days>::type>
+gps_clock::to_local(const gps_time<Duration>& t) NOEXCEPT
+{
+    using CD = typename std::common_type<Duration, date::days>::type;
+    return local_time<CD>{t.time_since_epoch()} +
+            (local_days(year{1980}/January/Sunday[1]) - local_days(year{1970}/January/1));
+}
+
+template <class Duration>
+inline
+gps_time<typename std::common_type<Duration, date::days>::type>
+gps_clock::from_local(const local_time<Duration>& t) NOEXCEPT
+{
+    using CD = typename std::common_type<Duration, date::days>::type;
+    return gps_time<CD>{t.time_since_epoch()} -
+            (local_days(year{1980}/January/Sunday[1]) - local_days(year{1970}/January/1));
+}
+
+
+template <class CharT, class Traits, class Duration>
+std::basic_ostream<CharT, Traits>&
+to_stream(std::basic_ostream<CharT, Traits>& os, const CharT* fmt,
+          const gps_time<Duration>& t)
+{
+    const std::string abbrev("GPS");
+    CONSTDATA std::chrono::seconds offset{0};
+    return to_stream(os, fmt, gps_clock::to_local(t), &abbrev, &offset);
+}
+
+template <class CharT, class Traits, class Duration>
+std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& os, const gps_time<Duration>& t)
+{
+    const CharT fmt[] = {'%', 'F', ' ', '%', 'T', CharT{}};
+    return to_stream(os, fmt, t);
+}
+
+template <class Duration, class CharT, class Traits, class Alloc = std::allocator<CharT>>
+std::basic_istream<CharT, Traits>&
+from_stream(std::basic_istream<CharT, Traits>& is, const CharT* fmt,
+            gps_time<Duration>& tp,
+            std::basic_string<CharT, Traits, Alloc>* abbrev = nullptr,
+            std::chrono::minutes* offset = nullptr)
+{
+    local_time<Duration> lp;
+    from_stream(is, fmt, lp, abbrev, offset);
+    if (!is.fail())
+        tp = gps_clock::from_local(lp);
+    return is;
+}
+
+// clock_time_conversion
+
+template <class DstClock, class SrcClock>
+struct clock_time_conversion
+{};
+
+template <>
+struct clock_time_conversion<std::chrono::system_clock, std::chrono::system_clock>
+{
+    template <class Duration>
+    CONSTCD14
+    sys_time<Duration>
+    operator()(const sys_time<Duration>& st) const
+    {
+        return st;
+    }
+};
+
+template <>
+struct clock_time_conversion<utc_clock, utc_clock>
+{
+    template <class Duration>
+    CONSTCD14
+    utc_time<Duration>
+    operator()(const utc_time<Duration>& ut) const
+    {
+        return ut;
+    }
+};
+
+template<>
+struct clock_time_conversion<local_t, local_t>
+{
+    template <class Duration>
+    CONSTCD14
+    local_time<Duration>
+    operator()(const local_time<Duration>& lt) const
+    {
+        return lt;
+    }
+};
+
+template <>
+struct clock_time_conversion<utc_clock, std::chrono::system_clock>
+{
+    template <class Duration>
+    utc_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+    operator()(const sys_time<Duration>& st) const
+    {
+        return utc_clock::from_sys(st);
+    }
+};
+
+template <>
+struct clock_time_conversion<std::chrono::system_clock, utc_clock>
+{
+    template <class Duration>
+    sys_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+    operator()(const utc_time<Duration>& ut) const
+    {
+        return utc_clock::to_sys(ut);
+    }
+};
+
+template<>
+struct clock_time_conversion<local_t, std::chrono::system_clock>
+{
+    template <class Duration>
+    CONSTCD14
+    local_time<Duration>
+    operator()(const sys_time<Duration>& st) const
+    {
+       return local_time<Duration>{st.time_since_epoch()};
+    }
+};
+
+template<>
+struct clock_time_conversion<std::chrono::system_clock, local_t>
+{
+    template <class Duration>
+    CONSTCD14
+    sys_time<Duration>
+    operator()(const local_time<Duration>& lt) const
+    {
+        return sys_time<Duration>{lt.time_since_epoch()};
+    }
+};
+
+template<>
+struct clock_time_conversion<utc_clock, local_t>
+{
+    template <class Duration>
+    utc_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+    operator()(const local_time<Duration>& lt) const
+    {
+       return utc_clock::from_local(lt);
+    }
+};
+
+template<>
+struct clock_time_conversion<local_t, utc_clock>
+{
+    template <class Duration>
+    local_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+    operator()(const utc_time<Duration>& ut) const
+    {
+       return utc_clock::to_local(ut);
+    }
+};
+
+template<typename Clock>
+struct clock_time_conversion<Clock, Clock>
+{
+    template <class Duration>
+    CONSTCD14
+    std::chrono::time_point<Clock, Duration>
+    operator()(const std::chrono::time_point<Clock, Duration>& tp) const
+    {
+        return tp;
+    }
+};
+
+namespace ctc_detail
+{
+
+template <class Clock, class Duration>
+    using time_point = std::chrono::time_point<Clock, Duration>;
+
+using std::declval;
+using std::chrono::system_clock;
+
+//Check if TimePoint is time for given clock,
+//if not emits hard error
+template <class Clock, class TimePoint>
+struct return_clock_time
+{
+    using clock_time_point = time_point<Clock, typename TimePoint::duration>;
+    using type             = TimePoint;
+
+    static_assert(std::is_same<TimePoint, clock_time_point>::value,
+                  "time point with appropariate clock shall be returned");
+};
+
+// Check if Clock has to_sys method accepting TimePoint with given duration const& and
+// returning sys_time. If so has nested type member equal to return type to_sys.
+template <class Clock, class Duration, class = void>
+struct return_to_sys
+{};
+
+template <class Clock, class Duration>
+struct return_to_sys
+       <
+           Clock, Duration,
+           decltype(Clock::to_sys(declval<time_point<Clock, Duration> const&>()), void())
+       >
+    : return_clock_time
+      <
+          system_clock,
+          decltype(Clock::to_sys(declval<time_point<Clock, Duration> const&>()))
+      >
+{};
+
+// Similiar to above
+template <class Clock, class Duration, class = void>
+struct return_from_sys
+{};
+
+template <class Clock, class Duration>
+struct return_from_sys
+       <
+           Clock, Duration,
+           decltype(Clock::from_sys(declval<time_point<system_clock, Duration> const&>()),
+                    void())
+       >
+    : return_clock_time
+      <
+          Clock,
+          decltype(Clock::from_sys(declval<time_point<system_clock, Duration> const&>()))
+      >
+{};
+
+// Similiar to above
+template <class Clock, class Duration, class = void>
+struct return_to_utc
+{};
+
+template <class Clock, class Duration>
+struct return_to_utc
+       <
+           Clock, Duration,
+           decltype(Clock::to_utc(declval<time_point<Clock, Duration> const&>()), void())
+       >
+    : return_clock_time
+      <
+          utc_clock,
+          decltype(Clock::to_utc(declval<time_point<Clock, Duration> const&>()))>
+{};
+
+// Similiar to above
+template <class Clock, class Duration, class = void>
+struct return_from_utc
+{};
+
+template <class Clock, class Duration>
+struct return_from_utc
+       <
+           Clock, Duration,
+           decltype(Clock::from_utc(declval<time_point<utc_clock, Duration> const&>()),
+                    void())
+       >
+    : return_clock_time
+      <
+          Clock,
+          decltype(Clock::from_utc(declval<time_point<utc_clock, Duration> const&>()))
+      >
+{};
+
+// Similiar to above
+template<typename Clock, typename Duration, typename = void>
+struct return_to_local
+{};
+
+template<typename Clock, typename Duration>
+struct return_to_local
+       <
+          Clock, Duration,
+          decltype(Clock::to_local(declval<time_point<Clock, Duration> const&>()),
+                   void())
+       >
+     : return_clock_time
+       <
+           local_t,
+           decltype(Clock::to_local(declval<time_point<Clock, Duration> const&>()))
+       >
+{};
+
+// Similiar to above
+template<typename Clock, typename Duration, typename = void>
+struct return_from_local
+{};
+
+template<typename Clock, typename Duration>
+struct return_from_local
+       <
+           Clock, Duration,
+           decltype(Clock::from_local(declval<time_point<local_t, Duration> const&>()),
+                    void())
+       >
+     : return_clock_time
+       <
+           Clock,
+           decltype(Clock::from_local(declval<time_point<local_t, Duration> const&>()))
+       >
+{};
+
+}  // namespace ctc_detail
+
+template <class SrcClock>
+struct clock_time_conversion<std::chrono::system_clock, SrcClock>
+{
+    template <class Duration>
+    CONSTCD14
+    typename ctc_detail::return_to_sys<SrcClock, Duration>::type
+    operator()(const std::chrono::time_point<SrcClock, Duration>& tp) const
+    {
+        return SrcClock::to_sys(tp);
+    }
+};
+
+template <class DstClock>
+struct clock_time_conversion<DstClock, std::chrono::system_clock>
+{
+    template <class Duration>
+    CONSTCD14
+    typename ctc_detail::return_from_sys<DstClock, Duration>::type
+    operator()(const sys_time<Duration>& st) const
+    {
+        return DstClock::from_sys(st);
+    }
+};
+
+template <class SrcClock>
+struct clock_time_conversion<utc_clock, SrcClock>
+{
+    template <class Duration>
+    CONSTCD14
+    typename ctc_detail::return_to_utc<SrcClock, Duration>::type
+    operator()(const std::chrono::time_point<SrcClock, Duration>& tp) const
+    {
+        return SrcClock::to_utc(tp);
+    }
+};
+
+template <class DstClock>
+struct clock_time_conversion<DstClock, utc_clock>
+{
+    template <class Duration>
+    CONSTCD14
+    typename ctc_detail::return_from_utc<DstClock, Duration>::type
+    operator()(const utc_time<Duration>& ut) const
+    {
+        return DstClock::from_utc(ut);
+    }
+};
+
+template<typename SrcClock>
+struct clock_time_conversion<local_t, SrcClock>
+{
+    template <class Duration>
+    CONSTCD14
+    typename ctc_detail::return_to_local<SrcClock, Duration>::type
+    operator()(const std::chrono::time_point<SrcClock, Duration>& tp) const
+    {
+        return SrcClock::to_local(tp);
+    }
+};
+
+template<typename DstClock>
+struct clock_time_conversion<DstClock, local_t>
+{
+    template <class Duration>
+    CONSTCD14
+    typename ctc_detail::return_from_local<DstClock, Duration>::type
+    operator()(const local_time<Duration>& lt) const
+    {
+        return DstClock::from_local(lt);
+    }
+};
+
+namespace clock_cast_detail
+{
+
+template <class Clock, class Duration>
+    using time_point = std::chrono::time_point<Clock, Duration>;
+using std::chrono::system_clock;
+
+template <class DstClock, class SrcClock, class Duration>
+CONSTCD14
+auto
+conv_clock(const time_point<SrcClock, Duration>& t)
+    -> decltype(std::declval<clock_time_conversion<DstClock, SrcClock>>()(t))
+{
+    return clock_time_conversion<DstClock, SrcClock>{}(t);
+}
+
+//direct trait conversion, 1st candidate
+template <class DstClock, class SrcClock, class Duration>
+CONSTCD14
+auto
+cc_impl(const time_point<SrcClock, Duration>& t, const time_point<SrcClock, Duration>*)
+    -> decltype(conv_clock<DstClock>(t))
+{
+    return conv_clock<DstClock>(t);
+}
+
+//conversion through sys, 2nd candidate
+template <class DstClock, class SrcClock, class Duration>
+CONSTCD14
+auto
+cc_impl(const time_point<SrcClock, Duration>& t, const void*)
+    -> decltype(conv_clock<DstClock>(conv_clock<system_clock>(t)))
+{
+    return conv_clock<DstClock>(conv_clock<system_clock>(t));
+}
+
+//conversion through utc, 2nd candidate
+template <class DstClock, class SrcClock, class Duration>
+CONSTCD14
+auto
+cc_impl(const time_point<SrcClock, Duration>& t, const void*)
+    -> decltype(0,  // MSVC_WORKAROUND
+                conv_clock<DstClock>(conv_clock<utc_clock>(t)))
+{
+    return conv_clock<DstClock>(conv_clock<utc_clock>(t));
+}
+
+//conversion through sys and utc, 3rd candidate
+template <class DstClock, class SrcClock, class Duration>
+CONSTCD14
+auto
+cc_impl(const time_point<SrcClock, Duration>& t, ...)
+    -> decltype(conv_clock<DstClock>(conv_clock<utc_clock>(conv_clock<system_clock>(t))))
+{
+    return conv_clock<DstClock>(conv_clock<utc_clock>(conv_clock<system_clock>(t)));
+}
+
+//conversion through utc and sys, 3rd candidate
+template <class DstClock, class SrcClock, class Duration>
+CONSTCD14
+auto
+cc_impl(const time_point<SrcClock, Duration>& t, ...)
+    -> decltype(0,  // MSVC_WORKAROUND
+                conv_clock<DstClock>(conv_clock<system_clock>(conv_clock<utc_clock>(t))))
+{
+    return conv_clock<DstClock>(conv_clock<system_clock>(conv_clock<utc_clock>(t)));
+}
+
+}  // namespace clock_cast_detail
+
+template <class DstClock, class SrcClock, class Duration>
+CONSTCD14
+auto
+clock_cast(const std::chrono::time_point<SrcClock, Duration>& tp)
+    -> decltype(clock_cast_detail::cc_impl<DstClock>(tp, &tp))
+{
+    return clock_cast_detail::cc_impl<DstClock>(tp, &tp);
+}
+
+// Deprecated API
+
+template <class Duration>
+inline
+sys_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+to_sys_time(const utc_time<Duration>& t)
+{
+    return utc_clock::to_sys(t);
+}
+
+template <class Duration>
+inline
+sys_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+to_sys_time(const tai_time<Duration>& t)
+{
+    return utc_clock::to_sys(tai_clock::to_utc(t));
+}
+
+template <class Duration>
+inline
+sys_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+to_sys_time(const gps_time<Duration>& t)
+{
+    return utc_clock::to_sys(gps_clock::to_utc(t));
+}
+
+
+template <class Duration>
+inline
+utc_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+to_utc_time(const sys_time<Duration>& t)
+{
+    return utc_clock::from_sys(t);
+}
+
+template <class Duration>
+inline
+utc_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+to_utc_time(const tai_time<Duration>& t)
+{
+    return tai_clock::to_utc(t);
+}
+
+template <class Duration>
+inline
+utc_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+to_utc_time(const gps_time<Duration>& t)
+{
+    return gps_clock::to_utc(t);
+}
+
+
+template <class Duration>
+inline
+tai_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+to_tai_time(const sys_time<Duration>& t)
+{
+    return tai_clock::from_utc(utc_clock::from_sys(t));
+}
+
+template <class Duration>
+inline
+tai_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+to_tai_time(const utc_time<Duration>& t)
+{
+    return tai_clock::from_utc(t);
+}
+
+template <class Duration>
+inline
+tai_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+to_tai_time(const gps_time<Duration>& t)
+{
+    return tai_clock::from_utc(gps_clock::to_utc(t));
+}
+
+
+template <class Duration>
+inline
+gps_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+to_gps_time(const sys_time<Duration>& t)
+{
+    return gps_clock::from_utc(utc_clock::from_sys(t));
+}
+
+template <class Duration>
+inline
+gps_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+to_gps_time(const utc_time<Duration>& t)
+{
+    return gps_clock::from_utc(t);
+}
+
+template <class Duration>
+inline
+gps_time<typename std::common_type<Duration, std::chrono::seconds>::type>
+to_gps_time(const tai_time<Duration>& t)
+{
+    return gps_clock::from_utc(tai_clock::to_utc(t));
+}
+
+}  // namespace date
+
+#endif  // TZ_H
diff --git a/third_party/date-3.0.1/include/date/tz_private.h b/third_party/date-3.0.1/include/date/tz_private.h
new file mode 100644
index 00000000..aec01d04
--- /dev/null
+++ b/third_party/date-3.0.1/include/date/tz_private.h
@@ -0,0 +1,316 @@
+#ifndef TZ_PRIVATE_H
+#define TZ_PRIVATE_H
+
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+//
+// Our apologies.  When the previous paragraph was written, lowercase had not yet
+// been invented (that would involve another several millennia of evolution).
+// We did not mean to shout.
+
+#if !defined(_MSC_VER) || (_MSC_VER >= 1900)
+#include "tz.h"
+#else
+#include "date.h"
+#include <vector>
+#endif
+
+namespace date
+{
+
+namespace detail
+{
+
+#if !USE_OS_TZDB
+
+enum class tz {utc, local, standard};
+
+//forward declare to avoid warnings in gcc 6.2
+class MonthDayTime;
+std::istream& operator>>(std::istream& is, MonthDayTime& x);
+std::ostream& operator<<(std::ostream& os, const MonthDayTime& x);
+
+
+class MonthDayTime
+{
+private:
+    struct pair
+    {
+#if defined(_MSC_VER) && (_MSC_VER < 1900)
+        pair() : month_day_(date::jan / 1), weekday_(0U) {}
+
+        pair(const date::month_day& month_day, const date::weekday& weekday)
+            : month_day_(month_day), weekday_(weekday) {}
+#endif
+
+        date::month_day month_day_;
+        date::weekday   weekday_;
+    };
+
+    enum Type {month_day, month_last_dow, lteq, gteq};
+
+    Type                         type_{month_day};
+
+#if !defined(_MSC_VER) || (_MSC_VER >= 1900)
+    union U
+#else
+    struct U
+#endif
+    {
+        date::month_day          month_day_;
+        date::month_weekday_last month_weekday_last_;
+        pair                     month_day_weekday_;
+
+#if !defined(_MSC_VER) || (_MSC_VER >= 1900)
+        U() : month_day_{date::jan/1} {}
+#else
+        U() :
+            month_day_(date::jan/1),
+            month_weekday_last_(date::month(0U), date::weekday_last(date::weekday(0U)))
+        {}
+
+#endif // !defined(_MSC_VER) || (_MSC_VER >= 1900)
+
+        U& operator=(const date::month_day& x);
+        U& operator=(const date::month_weekday_last& x);
+        U& operator=(const pair& x);
+    } u;
+
+    std::chrono::hours           h_{0};
+    std::chrono::minutes         m_{0};
+    std::chrono::seconds         s_{0};
+    tz                           zone_{tz::local};
+
+public:
+    MonthDayTime() = default;
+    MonthDayTime(local_seconds tp, tz timezone);
+    MonthDayTime(const date::month_day& md, tz timezone);
+
+    date::day day() const;
+    date::month month() const;
+    tz zone() const {return zone_;}
+
+    void canonicalize(date::year y);
+
+    sys_seconds
+       to_sys(date::year y, std::chrono::seconds offset, std::chrono::seconds save) const;
+    sys_days to_sys_days(date::year y) const;
+
+    sys_seconds to_time_point(date::year y) const;
+    int compare(date::year y, const MonthDayTime& x, date::year yx,
+                std::chrono::seconds offset, std::chrono::minutes prev_save) const;
+
+    friend std::istream& operator>>(std::istream& is, MonthDayTime& x);
+    friend std::ostream& operator<<(std::ostream& os, const MonthDayTime& x);
+};
+
+// A Rule specifies one or more set of datetimes without using an offset.
+// Multiple dates are specified with multiple years.  The years in effect
+// go from starting_year_ to ending_year_, inclusive.  starting_year_ <=
+// ending_year_. save_ is in effect for times from the specified time
+// onward, including the specified time. When the specified time is
+// local, it uses the save_ from the chronologically previous Rule, or if
+// there is none, 0.
+
+//forward declare to avoid warnings in gcc 6.2
+class Rule;
+bool operator==(const Rule& x, const Rule& y);
+bool operator<(const Rule& x, const Rule& y);
+bool operator==(const Rule& x, const date::year& y);
+bool operator<(const Rule& x, const date::year& y);
+bool operator==(const date::year& x, const Rule& y);
+bool operator<(const date::year& x, const Rule& y);
+bool operator==(const Rule& x, const std::string& y);
+bool operator<(const Rule& x, const std::string& y);
+bool operator==(const std::string& x, const Rule& y);
+bool operator<(const std::string& x, const Rule& y);
+std::ostream& operator<<(std::ostream& os, const Rule& r);
+
+class Rule
+{
+private:
+    std::string          name_;
+    date::year           starting_year_{0};
+    date::year           ending_year_{0};
+    MonthDayTime         starting_at_;
+    std::chrono::minutes save_{0};
+    std::string          abbrev_;
+
+public:
+    Rule() = default;
+    explicit Rule(const std::string& s);
+    Rule(const Rule& r, date::year starting_year, date::year ending_year);
+
+    const std::string& name() const {return name_;}
+    const std::string& abbrev() const {return abbrev_;}
+
+    const MonthDayTime&         mdt()           const {return starting_at_;}
+    const date::year&           starting_year() const {return starting_year_;}
+    const date::year&           ending_year()   const {return ending_year_;}
+    const std::chrono::minutes& save()          const {return save_;}
+
+    static void split_overlaps(std::vector<Rule>& rules);
+
+    friend bool operator==(const Rule& x, const Rule& y);
+    friend bool operator<(const Rule& x, const Rule& y);
+    friend bool operator==(const Rule& x, const date::year& y);
+    friend bool operator<(const Rule& x, const date::year& y);
+    friend bool operator==(const date::year& x, const Rule& y);
+    friend bool operator<(const date::year& x, const Rule& y);
+    friend bool operator==(const Rule& x, const std::string& y);
+    friend bool operator<(const Rule& x, const std::string& y);
+    friend bool operator==(const std::string& x, const Rule& y);
+    friend bool operator<(const std::string& x, const Rule& y);
+
+    friend std::ostream& operator<<(std::ostream& os, const Rule& r);
+
+private:
+    date::day day() const;
+    date::month month() const;
+    static void split_overlaps(std::vector<Rule>& rules, std::size_t i, std::size_t& e);
+    static bool overlaps(const Rule& x, const Rule& y);
+    static void split(std::vector<Rule>& rules, std::size_t i, std::size_t k,
+                      std::size_t& e);
+};
+
+inline bool operator!=(const Rule& x, const Rule& y) {return !(x == y);}
+inline bool operator> (const Rule& x, const Rule& y) {return   y < x;}
+inline bool operator<=(const Rule& x, const Rule& y) {return !(y < x);}
+inline bool operator>=(const Rule& x, const Rule& y) {return !(x < y);}
+
+inline bool operator!=(const Rule& x, const date::year& y) {return !(x == y);}
+inline bool operator> (const Rule& x, const date::year& y) {return   y < x;}
+inline bool operator<=(const Rule& x, const date::year& y) {return !(y < x);}
+inline bool operator>=(const Rule& x, const date::year& y) {return !(x < y);}
+
+inline bool operator!=(const date::year& x, const Rule& y) {return !(x == y);}
+inline bool operator> (const date::year& x, const Rule& y) {return   y < x;}
+inline bool operator<=(const date::year& x, const Rule& y) {return !(y < x);}
+inline bool operator>=(const date::year& x, const Rule& y) {return !(x < y);}
+
+inline bool operator!=(const Rule& x, const std::string& y) {return !(x == y);}
+inline bool operator> (const Rule& x, const std::string& y) {return   y < x;}
+inline bool operator<=(const Rule& x, const std::string& y) {return !(y < x);}
+inline bool operator>=(const Rule& x, const std::string& y) {return !(x < y);}
+
+inline bool operator!=(const std::string& x, const Rule& y) {return !(x == y);}
+inline bool operator> (const std::string& x, const Rule& y) {return   y < x;}
+inline bool operator<=(const std::string& x, const Rule& y) {return !(y < x);}
+inline bool operator>=(const std::string& x, const Rule& y) {return !(x < y);}
+
+struct zonelet
+{
+    enum tag {has_rule, has_save, is_empty};
+
+    std::chrono::seconds gmtoff_;
+    tag tag_ = has_rule;
+
+#if !defined(_MSC_VER) || (_MSC_VER >= 1900)
+    union U
+#else
+    struct U
+#endif
+    {
+        std::string          rule_;
+        std::chrono::minutes save_;
+
+        ~U() {}
+        U() {}
+        U(const U&) {}
+        U& operator=(const U&) = delete;
+    } u;
+
+    std::string                        format_;
+    date::year                         until_year_{0};
+    MonthDayTime                       until_date_;
+    sys_seconds                        until_utc_;
+    local_seconds                      until_std_;
+    local_seconds                      until_loc_;
+    std::chrono::minutes               initial_save_{0};
+    std::string                        initial_abbrev_;
+    std::pair<const Rule*, date::year> first_rule_{nullptr, date::year::min()};
+    std::pair<const Rule*, date::year> last_rule_{nullptr, date::year::max()};
+
+    ~zonelet();
+    zonelet();
+    zonelet(const zonelet& i);
+    zonelet& operator=(const zonelet&) = delete;
+};
+
+#else  // USE_OS_TZDB
+
+struct ttinfo
+{
+    std::int32_t  tt_gmtoff;
+    unsigned char tt_isdst;
+    unsigned char tt_abbrind;
+    unsigned char pad[2];
+};
+
+static_assert(sizeof(ttinfo) == 8, "");
+
+struct expanded_ttinfo
+{
+    std::chrono::seconds offset;
+    std::string          abbrev;
+    bool                 is_dst;
+};
+
+struct transition
+{
+    sys_seconds            timepoint;
+    const expanded_ttinfo* info;
+
+    transition(sys_seconds tp, const expanded_ttinfo* i = nullptr)
+        : timepoint(tp)
+        , info(i)
+        {}
+
+    friend
+    std::ostream&
+    operator<<(std::ostream& os, const transition& t)
+    {
+        using date::operator<<;
+        os << t.timepoint << "Z ";
+        if (t.info->offset >= std::chrono::seconds{0})
+            os << '+';
+        os << make_time(t.info->offset);
+        if (t.info->is_dst > 0)
+            os << " daylight ";
+        else
+            os << " standard ";
+        os << t.info->abbrev;
+        return os;
+    }
+};
+
+#endif  // USE_OS_TZDB
+
+}  // namespace detail
+
+}  // namespace date
+
+#if defined(_MSC_VER) && (_MSC_VER < 1900)
+#include "tz.h"
+#endif
+
+#endif  // TZ_PRIVATE_H
diff --git a/third_party/date-3.0.1/src/ios.mm b/third_party/date-3.0.1/src/ios.mm
new file mode 100644
index 00000000..fe3bb241
--- /dev/null
+++ b/third_party/date-3.0.1/src/ios.mm
@@ -0,0 +1,337 @@
+//
+// The MIT License (MIT)
+//
+// Copyright (c) 2016 Alexander Kormanovsky
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+//
+
+#include "date/ios.h"
+
+#if TARGET_OS_IPHONE
+
+#include <Foundation/Foundation.h>
+
+#include <fstream>
+#include <zlib.h>
+#include <sys/stat.h>
+
+#ifndef TAR_DEBUG
+#  define TAR_DEBUG 0
+#endif
+
+#define INTERNAL_DIR        "Library"
+#define TZDATA_DIR          "tzdata"
+#define TARGZ_EXTENSION     "tar.gz"
+
+#define TAR_BLOCK_SIZE                  512
+#define TAR_TYPE_POSITION               156
+#define TAR_NAME_POSITION               0
+#define TAR_NAME_SIZE                   100
+#define TAR_SIZE_POSITION               124
+#define TAR_SIZE_SIZE                   12
+
+namespace date
+{
+    namespace iOSUtils
+    {
+        
+        struct TarInfo
+        {
+            char objType;
+            std::string objName;
+            size_t realContentSize; // writable size without padding zeroes
+            size_t blocksContentSize; // adjusted size to 512 bytes blocks
+            bool success;
+        };
+        
+        std::string convertCFStringRefPathToCStringPath(CFStringRef ref);
+        bool extractTzdata(CFURLRef homeUrl, CFURLRef archiveUrl, std::string destPath);
+        TarInfo getTarObjectInfo(std::ifstream &readStream);
+        std::string getTarObject(std::ifstream &readStream, int64_t size);
+        bool writeFile(const std::string &tzdataPath, const std::string &fileName,
+                       const std::string &data, size_t realContentSize);
+        
+        std::string
+        get_current_timezone()
+        {
+            CFTimeZoneRef tzRef = CFTimeZoneCopySystem();
+            CFStringRef tzNameRef = CFTimeZoneGetName(tzRef);
+            CFIndex bufferSize = CFStringGetLength(tzNameRef) + 1;
+            char buffer[bufferSize];
+            
+            if (CFStringGetCString(tzNameRef, buffer, bufferSize, kCFStringEncodingUTF8))
+            {
+                CFRelease(tzRef);
+                return std::string(buffer);
+            }
+            
+            CFRelease(tzRef);
+            
+            return "";
+        }
+        
+        std::string
+        get_tzdata_path()
+        {
+            CFURLRef homeUrlRef = CFCopyHomeDirectoryURL();
+            CFStringRef homePath = CFURLCopyPath(homeUrlRef);
+            std::string path(std::string(convertCFStringRefPathToCStringPath(homePath)) +
+                             INTERNAL_DIR + "/" + TZDATA_DIR);
+            std::string result_path(std::string(convertCFStringRefPathToCStringPath(homePath)) +
+                                    INTERNAL_DIR);
+            
+            if (access(path.c_str(), F_OK) == 0)
+            {
+#if TAR_DEBUG
+                printf("tzdata dir exists\n");
+#endif
+                CFRelease(homeUrlRef);
+                CFRelease(homePath);
+                
+                return result_path;
+            }
+            
+            CFBundleRef mainBundle = CFBundleGetMainBundle();
+            CFArrayRef paths = CFBundleCopyResourceURLsOfType(mainBundle, CFSTR(TARGZ_EXTENSION),
+                                                              NULL);
+            
+            if (CFArrayGetCount(paths) != 0)
+            {
+                // get archive path, assume there is no other tar.gz in bundle
+                CFURLRef archiveUrl = static_cast<CFURLRef>(CFArrayGetValueAtIndex(paths, 0));
+                CFStringRef archiveName = CFURLCopyPath(archiveUrl);
+                archiveUrl = CFBundleCopyResourceURL(mainBundle, archiveName, NULL, NULL);
+                
+                extractTzdata(homeUrlRef, archiveUrl, path);
+                
+                CFRelease(archiveUrl);
+                CFRelease(archiveName);
+            }
+            
+            CFRelease(homeUrlRef);
+            CFRelease(homePath);
+            CFRelease(paths);
+            
+            return result_path;
+        }
+        
+        std::string
+        convertCFStringRefPathToCStringPath(CFStringRef ref)
+        {
+            CFIndex bufferSize = CFStringGetMaximumSizeOfFileSystemRepresentation(ref);
+            char *buffer = new char[bufferSize];
+            CFStringGetFileSystemRepresentation(ref, buffer, bufferSize);
+            auto result = std::string(buffer);
+            delete[] buffer;
+            return result;
+        }
+        
+        bool
+        extractTzdata(CFURLRef homeUrl, CFURLRef archiveUrl, std::string destPath)
+        {
+            std::string TAR_TMP_PATH = "/tmp.tar";
+            
+            CFStringRef homeStringRef = CFURLCopyPath(homeUrl);
+            auto homePath = convertCFStringRefPathToCStringPath(homeStringRef);
+            CFRelease(homeStringRef);
+            
+            CFStringRef archiveStringRef = CFURLCopyPath(archiveUrl);
+            auto archivePath = convertCFStringRefPathToCStringPath(archiveStringRef);
+            CFRelease(archiveStringRef);
+            
+            // create Library path
+            auto libraryPath = homePath + INTERNAL_DIR;
+            
+            // create tzdata path
+            auto tzdataPath = libraryPath + "/" + TZDATA_DIR;
+            
+            // -- replace %20 with " "
+            const std::string search = "%20";
+            const std::string replacement = " ";
+            size_t pos = 0;
+            
+            while ((pos = archivePath.find(search, pos)) != std::string::npos) {
+                archivePath.replace(pos, search.length(), replacement);
+                pos += replacement.length();
+            }
+            
+            gzFile tarFile = gzopen(archivePath.c_str(), "rb");
+            
+            // create tar unpacking path
+            auto tarPath = libraryPath + TAR_TMP_PATH;
+            
+            // create tzdata directory
+            mkdir(destPath.c_str(), S_IRWXU | S_IRWXG | S_IROTH | S_IXOTH);
+            
+            // ======= extract tar ========
+            
+            std::ofstream os(tarPath.c_str(), std::ofstream::out | std::ofstream::app);
+            unsigned int bufferLength = 1024 * 256;  // 256Kb
+            unsigned char *buffer = (unsigned char *)malloc(bufferLength);
+            bool success = true;
+            
+            while (true)
+            {
+                int readBytes = gzread(tarFile, buffer, bufferLength);
+                
+                if (readBytes > 0)
+                {
+                    os.write((char *) &buffer[0], readBytes);
+                }
+                else
+                    if (readBytes == 0)
+                    {
+                        break;
+                    }
+                    else
+                        if (readBytes == -1)
+                        {
+                            printf("decompression failed\n");
+                            success = false;
+                            break;
+                        }
+                        else
+                        {
+                            printf("unexpected zlib state\n");
+                            success = false;
+                            break;
+                        }
+            }
+            
+            os.close();
+            free(buffer);
+            gzclose(tarFile);
+            
+            if (!success)
+            {
+                remove(tarPath.c_str());
+                return false;
+            }
+            
+            // ======== extract files =========
+            
+            uint64_t location = 0; // Position in the file
+            
+            // get file size
+            struct stat stat_buf;
+            int res = stat(tarPath.c_str(), &stat_buf);
+            if (res != 0)
+            {
+                printf("error file size\n");
+                remove(tarPath.c_str());
+                return false;
+            }
+            int64_t tarSize = stat_buf.st_size;
+            
+            // create read stream
+            std::ifstream is(tarPath.c_str(), std::ifstream::in | std::ifstream::binary);
+            
+            // process files
+            while (location < tarSize)
+            {
+                TarInfo info = getTarObjectInfo(is);
+                
+                if (!info.success || info.realContentSize == 0)
+                {
+                    break; // something wrong or all files are read
+                }
+                
+                switch (info.objType)
+                {
+                    case '0':   // file
+                    case '\0':  //
+                    {
+                        std::string obj = getTarObject(is, info.blocksContentSize);
+#if TAR_DEBUG
+                        size += info.realContentSize;
+                        printf("#%i %s file size %lld written total %ld from %lld\n", ++count,
+                               info.objName.c_str(), info.realContentSize, size, tarSize);
+#endif
+                        writeFile(tzdataPath, info.objName, obj, info.realContentSize);
+                        location += info.blocksContentSize;
+                        
+                        break;
+                    }
+                }
+            }
+            
+            remove(tarPath.c_str());
+            
+            return true;
+        }
+        
+        TarInfo
+        getTarObjectInfo(std::ifstream &readStream)
+        {
+            int64_t length = TAR_BLOCK_SIZE;
+            char buffer[length];
+            char type;
+            char name[TAR_NAME_SIZE + 1];
+            char sizeBuf[TAR_SIZE_SIZE + 1];
+            
+            readStream.read(buffer, length);
+            
+            memcpy(&type, &buffer[TAR_TYPE_POSITION], 1);
+            
+            memset(&name, '\0', TAR_NAME_SIZE + 1);
+            memcpy(&name, &buffer[TAR_NAME_POSITION], TAR_NAME_SIZE);
+            
+            memset(&sizeBuf, '\0', TAR_SIZE_SIZE + 1);
+            memcpy(&sizeBuf, &buffer[TAR_SIZE_POSITION], TAR_SIZE_SIZE);
+            size_t realSize = strtol(sizeBuf, NULL, 8);
+            size_t blocksSize = realSize + (TAR_BLOCK_SIZE - (realSize % TAR_BLOCK_SIZE));
+            
+            return {type, std::string(name), realSize, blocksSize, true};
+        }
+        
+        std::string
+        getTarObject(std::ifstream &readStream, int64_t size)
+        {
+            char buffer[size];
+            readStream.read(buffer, size);
+            return std::string(buffer);
+        }
+        
+        bool
+        writeFile(const std::string &tzdataPath, const std::string &fileName, const std::string &data,
+                  size_t realContentSize)
+        {
+            std::ofstream os(tzdataPath + "/" + fileName, std::ofstream::out | std::ofstream::binary);
+            
+            if (!os) {
+                return false;
+            }
+            
+            // trim empty space
+            char trimmedData[realContentSize + 1];
+            memset(&trimmedData, '\0', realContentSize);
+            memcpy(&trimmedData, data.c_str(), realContentSize);
+            
+            // write
+            os.write(trimmedData, realContentSize);
+            os.close();
+            
+            return true;
+        }
+        
+    }  // namespace iOSUtils
+}  // namespace date
+
+#endif  // TARGET_OS_IPHONE
diff --git a/third_party/date-3.0.1/src/tz.cpp b/third_party/date-3.0.1/src/tz.cpp
new file mode 100644
index 00000000..26babbd9
--- /dev/null
+++ b/third_party/date-3.0.1/src/tz.cpp
@@ -0,0 +1,3944 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016, 2017 Howard Hinnant
+// Copyright (c) 2015 Ville Voutilainen
+// Copyright (c) 2016 Alexander Kormanovsky
+// Copyright (c) 2016, 2017 Jiangang Zhuang
+// Copyright (c) 2017 Nicolas Veloz Savino
+// Copyright (c) 2017 Florian Dang
+// Copyright (c) 2017 Aaron Bishop
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+//
+// Our apologies.  When the previous paragraph was written, lowercase had not yet
+// been invented (that would involve another several millennia of evolution).
+// We did not mean to shout.
+
+#ifdef _WIN32
+   // windows.h will be included directly and indirectly (e.g. by curl).
+   // We need to define these macros to prevent windows.h bringing in
+   // more than we need and do it early so windows.h doesn't get included
+   // without these macros having been defined.
+   // min/max macros interfere with the C++ versions.
+#  ifndef NOMINMAX
+#    define NOMINMAX
+#  endif
+   // We don't need all that Windows has to offer.
+#  ifndef WIN32_LEAN_AND_MEAN
+#    define WIN32_LEAN_AND_MEAN
+#  endif
+
+   // for wcstombs
+#  ifndef _CRT_SECURE_NO_WARNINGS
+#    define _CRT_SECURE_NO_WARNINGS
+#  endif
+
+   // None of this happens with the MS SDK (at least VS14 which I tested), but:
+   // Compiling with mingw, we get "error: 'KF_FLAG_DEFAULT' was not declared in this scope."
+   // and error: 'SHGetKnownFolderPath' was not declared in this scope.".
+   // It seems when using mingw NTDDI_VERSION is undefined and that
+   // causes KNOWN_FOLDER_FLAG and the KF_ flags to not get defined.
+   // So we must define NTDDI_VERSION to get those flags on mingw.
+   // The docs say though here:
+   // https://msdn.microsoft.com/en-nz/library/windows/desktop/aa383745(v=vs.85).aspx
+   // that "If you define NTDDI_VERSION, you must also define _WIN32_WINNT."
+   // So we declare we require Vista or greater.
+#  ifdef __MINGW32__
+
+#    ifndef NTDDI_VERSION
+#      define NTDDI_VERSION 0x06000000
+#      define _WIN32_WINNT _WIN32_WINNT_VISTA
+#    elif NTDDI_VERSION < 0x06000000
+#      warning "If this fails to compile NTDDI_VERSION may be to low. See comments above."
+#    endif
+     // But once we define the values above we then get this linker error:
+     // "tz.cpp:(.rdata$.refptr.FOLDERID_Downloads[.refptr.FOLDERID_Downloads]+0x0): "
+     //     "undefined reference to `FOLDERID_Downloads'"
+     // which #include <initguid.h> cures see:
+     // https://support.microsoft.com/en-us/kb/130869
+#    include <initguid.h>
+     // But with <initguid.h> included, the error moves on to:
+     // error: 'FOLDERID_Downloads' was not declared in this scope
+     // Which #include <knownfolders.h> cures.
+#    include <knownfolders.h>
+
+#  endif  // __MINGW32__
+
+#  include <windows.h>
+#endif  // _WIN32
+
+#include "date/tz_private.h"
+
+#ifdef __APPLE__
+#  include "date/ios.h"
+#else
+#  define TARGET_OS_IPHONE 0
+#  define TARGET_OS_SIMULATOR 0
+#endif
+
+#if USE_OS_TZDB
+#  include <dirent.h>
+#endif
+#include <algorithm>
+#include <cctype>
+#include <cstdlib>
+#include <cstring>
+#include <cwchar>
+#include <exception>
+#include <fstream>
+#include <iostream>
+#include <iterator>
+#include <memory>
+#if USE_OS_TZDB
+#  include <queue>
+#endif
+#include <sstream>
+#include <string>
+#include <tuple>
+#include <vector>
+#include <sys/stat.h>
+
+// unistd.h is used on some platforms as part of the the means to get
+// the current time zone. On Win32 windows.h provides a means to do it.
+// gcc/mingw supports unistd.h on Win32 but MSVC does not.
+
+#ifdef _WIN32
+#  ifdef WINAPI_FAMILY
+#    include <winapifamily.h>
+#    if WINAPI_FAMILY != WINAPI_FAMILY_DESKTOP_APP
+#      define WINRT
+#      define INSTALL .
+#    endif
+#  endif
+
+#  include <io.h> // _unlink etc.
+
+#  if defined(__clang__)
+    struct IUnknown;    // fix for issue with static_cast<> in objbase.h
+                        //   (see https://github.com/philsquared/Catch/issues/690)
+#  endif
+
+#  include <shlobj.h> // CoTaskFree, ShGetKnownFolderPath etc.
+#  if HAS_REMOTE_API
+#    include <direct.h> // _mkdir
+#    include <shellapi.h> // ShFileOperation etc.
+#  endif  // HAS_REMOTE_API
+#else   // !_WIN32
+#  include <unistd.h>
+#  if !USE_OS_TZDB && !defined(INSTALL)
+#    include <wordexp.h>
+#  endif
+#  include <limits.h>
+#  include <string.h>
+#  if !USE_SHELL_API
+#    include <sys/stat.h>
+#    include <sys/fcntl.h>
+#    include <dirent.h>
+#    include <cstring>
+#    include <sys/wait.h>
+#    include <sys/types.h>
+#  endif //!USE_SHELL_API
+#endif  // !_WIN32
+
+
+#if HAS_REMOTE_API
+   // Note curl includes windows.h so we must include curl AFTER definitions of things
+   // that affect windows.h such as NOMINMAX.
+#if defined(_MSC_VER) && defined(SHORTENED_CURL_INCLUDE)
+   // For rmt_curl nuget package
+#  include <curl.h>
+#else
+#  include <curl/curl.h>
+#endif
+#endif
+
+#ifdef _WIN32
+static CONSTDATA char folder_delimiter = '\\';
+#else   // !_WIN32
+static CONSTDATA char folder_delimiter = '/';
+#endif  // !_WIN32
+
+#if defined(__GNUC__) && __GNUC__ < 5
+   // GCC 4.9 Bug 61489 Wrong warning with -Wmissing-field-initializers
+#  pragma GCC diagnostic push
+#  pragma GCC diagnostic ignored "-Wmissing-field-initializers"
+#endif  // defined(__GNUC__) && __GNUC__ < 5
+
+#if !USE_OS_TZDB
+
+#  ifdef _WIN32
+#    ifndef WINRT
+
+namespace
+{
+    struct task_mem_deleter
+    {
+        void operator()(wchar_t buf[])
+        {
+            if (buf != nullptr)
+                CoTaskMemFree(buf);
+        }
+    };
+    using co_task_mem_ptr = std::unique_ptr<wchar_t[], task_mem_deleter>;
+}
+
+// We might need to know certain locations even if not using the remote API,
+// so keep these routines out of that block for now.
+static
+std::string
+get_known_folder(const GUID& folderid)
+{
+    std::string folder;
+    PWSTR pfolder = nullptr;
+    HRESULT hr = SHGetKnownFolderPath(folderid, KF_FLAG_DEFAULT, nullptr, &pfolder);
+    if (SUCCEEDED(hr))
+    {
+        co_task_mem_ptr folder_ptr(pfolder);
+        const wchar_t* fptr = folder_ptr.get();
+        auto state = std::mbstate_t();
+        const auto required = std::wcsrtombs(nullptr, &fptr, 0, &state);
+        if (required != 0 && required != std::size_t(-1))
+        {
+            folder.resize(required);
+            std::wcsrtombs(&folder[0], &fptr, folder.size(), &state);
+        }
+    }
+    return folder;
+}
+
+#      ifndef INSTALL
+
+// Usually something like "c:\Users\username\Downloads".
+static
+std::string
+get_download_folder()
+{
+    return get_known_folder(FOLDERID_Downloads);
+}
+
+#      endif  // !INSTALL
+
+#    endif // WINRT
+#  else // !_WIN32
+
+#    if !defined(INSTALL)
+
+static
+std::string
+expand_path(std::string path)
+{
+#      if TARGET_OS_IPHONE
+    return date::iOSUtils::get_tzdata_path();
+#      else  // !TARGET_OS_IPHONE
+    ::wordexp_t w{};
+    std::unique_ptr<::wordexp_t, void(*)(::wordexp_t*)> hold{&w, ::wordfree};
+    ::wordexp(path.c_str(), &w, 0);
+    if (w.we_wordc != 1)
+        throw std::runtime_error("Cannot expand path: " + path);
+    path = w.we_wordv[0];
+    return path;
+#      endif  // !TARGET_OS_IPHONE
+}
+
+static
+std::string
+get_download_folder()
+{
+    return expand_path("~/Downloads");
+}
+
+#    endif // !defined(INSTALL)
+
+#  endif  // !_WIN32
+
+#endif  // !USE_OS_TZDB
+
+namespace date
+{
+// +---------------------+
+// | Begin Configuration |
+// +---------------------+
+
+using namespace detail;
+
+#if !USE_OS_TZDB
+
+static
+std::string&
+access_install()
+{
+    static std::string install
+#ifndef INSTALL
+
+    = get_download_folder() + folder_delimiter + "tzdata";
+
+#else   // !INSTALL
+
+#  define STRINGIZEIMP(x) #x
+#  define STRINGIZE(x) STRINGIZEIMP(x)
+
+    = STRINGIZE(INSTALL) + std::string(1, folder_delimiter) + "tzdata";
+
+    #undef STRINGIZEIMP
+    #undef STRINGIZE
+#endif  // !INSTALL
+
+    return install;
+}
+
+void
+set_install(const std::string& s)
+{
+    access_install() = s;
+}
+
+static
+const std::string&
+get_install()
+{
+    static const std::string& ref = access_install();
+    return ref;
+}
+
+#if HAS_REMOTE_API
+static
+std::string
+get_download_gz_file(const std::string& version)
+{
+    auto file = get_install() + version + ".tar.gz";
+    return file;
+}
+#endif  // HAS_REMOTE_API
+
+#endif  // !USE_OS_TZDB
+
+// These can be used to reduce the range of the database to save memory
+CONSTDATA auto min_year = date::year::min();
+CONSTDATA auto max_year = date::year::max();
+
+CONSTDATA auto min_day = date::January/1;
+CONSTDATA auto max_day = date::December/31;
+
+#if USE_OS_TZDB
+
+CONSTCD14 const sys_seconds min_seconds = sys_days(min_year/min_day);
+
+#endif  // USE_OS_TZDB
+
+#ifndef _WIN32
+
+static
+std::string
+discover_tz_dir()
+{
+    struct stat sb;
+    using namespace std;
+#  ifndef __APPLE__
+    CONSTDATA auto tz_dir_default = "/usr/share/zoneinfo";
+    CONSTDATA auto tz_dir_buildroot = "/usr/share/zoneinfo/uclibc";
+
+    // Check special path which is valid for buildroot with uclibc builds
+    if(stat(tz_dir_buildroot, &sb) == 0 && S_ISDIR(sb.st_mode))
+        return tz_dir_buildroot;
+    else if(stat(tz_dir_default, &sb) == 0 && S_ISDIR(sb.st_mode))
+        return tz_dir_default;
+    else
+        throw runtime_error("discover_tz_dir failed to find zoneinfo\n");
+#  else  // __APPLE__
+#      if TARGET_OS_IPHONE
+#          if TARGET_OS_SIMULATOR
+    return "/usr/share/zoneinfo";
+#          else
+    return "/var/db/timezone/zoneinfo";
+#          endif
+#      else
+    CONSTDATA auto timezone = "/etc/localtime";
+    if (!(lstat(timezone, &sb) == 0 && S_ISLNK(sb.st_mode) && sb.st_size > 0))
+        throw runtime_error("discover_tz_dir failed\n");
+    string result;
+    char rp[PATH_MAX+1] = {};
+    if (readlink(timezone, rp, sizeof(rp)-1) > 0)
+        result = string(rp);
+    else
+        throw system_error(errno, system_category(), "readlink() failed");
+    auto i = result.find("zoneinfo");
+    if (i == string::npos)
+        throw runtime_error("discover_tz_dir failed to find zoneinfo\n");
+    i = result.find('/', i);
+    if (i == string::npos)
+        throw runtime_error("discover_tz_dir failed to find '/'\n");
+    return result.substr(0, i);
+#      endif
+#  endif  // __APPLE__
+}
+
+static
+const std::string&
+get_tz_dir()
+{
+    static const std::string tz_dir = discover_tz_dir();
+    return tz_dir;
+}
+
+#endif
+
+// +-------------------+
+// | End Configuration |
+// +-------------------+
+
+#ifndef _MSC_VER
+static_assert(min_year <= max_year, "Configuration error");
+#endif
+
+static std::unique_ptr<tzdb> init_tzdb();
+
+tzdb_list::~tzdb_list()
+{
+    const tzdb* ptr = head_;
+    head_ = nullptr;
+    while (ptr != nullptr)
+    {
+        auto next = ptr->next;
+        delete ptr;
+        ptr = next;
+    }
+}
+
+tzdb_list::tzdb_list(tzdb_list&& x) NOEXCEPT
+   : head_{x.head_.exchange(nullptr)}
+{
+}
+
+void
+tzdb_list::push_front(tzdb* tzdb) NOEXCEPT
+{
+    tzdb->next = head_;
+    head_ = tzdb;
+}
+
+tzdb_list::const_iterator
+tzdb_list::erase_after(const_iterator p) NOEXCEPT
+{
+    auto t = p.p_->next;
+    p.p_->next = p.p_->next->next;
+    delete t;
+    return ++p;
+}
+
+struct tzdb_list::undocumented_helper
+{
+    static void push_front(tzdb_list& db_list, tzdb* tzdb) NOEXCEPT
+    {
+        db_list.push_front(tzdb);
+    }
+};
+
+static
+tzdb_list
+create_tzdb()
+{
+    tzdb_list tz_db;
+    tzdb_list::undocumented_helper::push_front(tz_db, init_tzdb().release());
+    return tz_db;
+}
+
+tzdb_list&
+get_tzdb_list()
+{
+    static tzdb_list tz_db = create_tzdb();
+    return tz_db;
+}
+
+static
+std::string
+parse3(std::istream& in)
+{
+    std::string r(3, ' ');
+    ws(in);
+    r[0] = static_cast<char>(in.get());
+    r[1] = static_cast<char>(in.get());
+    r[2] = static_cast<char>(in.get());
+    return r;
+}
+
+static
+unsigned
+parse_month(std::istream& in)
+{
+    CONSTDATA char*const month_names[] =
+        {"Jan", "Feb", "Mar", "Apr", "May", "Jun",
+         "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"};
+    auto s = parse3(in);
+    auto m = std::find(std::begin(month_names), std::end(month_names), s) - month_names;
+    if (m >= std::end(month_names) - std::begin(month_names))
+        throw std::runtime_error("oops: bad month name: " + s);
+    return static_cast<unsigned>(++m);
+}
+
+#if !USE_OS_TZDB
+
+#ifdef _WIN32
+
+static
+void
+sort_zone_mappings(std::vector<date::detail::timezone_mapping>& mappings)
+{
+    std::sort(mappings.begin(), mappings.end(),
+        [](const date::detail::timezone_mapping& lhs,
+           const date::detail::timezone_mapping& rhs)->bool
+    {
+        auto other_result = lhs.other.compare(rhs.other);
+        if (other_result < 0)
+            return true;
+        else if (other_result == 0)
+        {
+            auto territory_result = lhs.territory.compare(rhs.territory);
+            if (territory_result < 0)
+                return true;
+            else if (territory_result == 0)
+            {
+                if (lhs.type < rhs.type)
+                    return true;
+            }
+        }
+        return false;
+    });
+}
+
+static
+bool
+native_to_standard_timezone_name(const std::string& native_tz_name,
+                                 std::string& standard_tz_name)
+{
+    // TOOD! Need be a case insensitive compare?
+    if (native_tz_name == "UTC")
+    {
+        standard_tz_name = "Etc/UTC";
+        return true;
+    }
+    standard_tz_name.clear();
+    // TODO! we can improve on linear search.
+    const auto& mappings = date::get_tzdb().mappings;
+    for (const auto& tzm : mappings)
+    {
+        if (tzm.other == native_tz_name)
+        {
+            standard_tz_name = tzm.type;
+            return true;
+        }
+    }
+    return false;
+}
+
+// Parse this XML file:
+// https://raw.githubusercontent.com/unicode-org/cldr/master/common/supplemental/windowsZones.xml
+// The parsing method is designed to be simple and quick. It is not overly
+// forgiving of change but it should diagnose basic format issues.
+// See timezone_mapping structure for more info.
+static
+std::vector<detail::timezone_mapping>
+load_timezone_mappings_from_xml_file(const std::string& input_path)
+{
+    std::size_t line_num = 0;
+    std::vector<detail::timezone_mapping> mappings;
+    std::string line;
+
+    std::ifstream is(input_path);
+    if (!is.is_open())
+    {
+        // We don't emit file exceptions because that's an implementation detail.
+        std::string msg = "Error opening time zone mapping file \"";
+        msg += input_path;
+        msg += "\".";
+        throw std::runtime_error(msg);
+    }
+
+    auto error = [&input_path, &line_num](const char* info)
+    {
+        std::string msg = "Error loading time zone mapping file \"";
+        msg += input_path;
+        msg += "\" at line ";
+        msg += std::to_string(line_num);
+        msg += ": ";
+        msg += info;
+        throw std::runtime_error(msg);
+    };
+    // [optional space]a="b"
+    auto read_attribute = [&line, &error]
+                          (const char* name, std::string& value, std::size_t startPos)
+                          ->std::size_t
+    {
+        value.clear();
+        // Skip leading space before attribute name.
+        std::size_t spos = line.find_first_not_of(' ', startPos);
+        if (spos == std::string::npos)
+            spos = startPos;
+        // Assume everything up to next = is the attribute name
+        // and that an = will always delimit that.
+        std::size_t epos = line.find('=', spos);
+        if (epos == std::string::npos)
+            error("Expected \'=\' right after attribute name.");
+        std::size_t name_len = epos - spos;
+        // Expect the name we find matches the name we expect.
+        if (line.compare(spos, name_len, name) != 0)
+        {
+            std::string msg;
+            msg = "Expected attribute name \'";
+            msg += name;
+            msg += "\' around position ";
+            msg += std::to_string(spos);
+            msg += " but found something else.";
+            error(msg.c_str());
+        }
+        ++epos; // Skip the '=' that is after the attribute name.
+        spos = epos;
+        if (spos < line.length() && line[spos] == '\"')
+            ++spos; // Skip the quote that is before the attribute value.
+        else
+        {
+            std::string msg = "Expected '\"' to begin value of attribute \'";
+            msg += name;
+            msg += "\'.";
+            error(msg.c_str());
+        }
+        epos = line.find('\"', spos);
+        if (epos == std::string::npos)
+        {
+            std::string msg = "Expected '\"' to end value of attribute \'";
+            msg += name;
+            msg += "\'.";
+            error(msg.c_str());
+        }
+        // Extract everything in between the quotes. Note no escaping is done.
+        std::size_t value_len = epos - spos;
+        value.assign(line, spos, value_len);
+        ++epos; // Skip the quote that is after the attribute value;
+        return epos;
+    };
+
+    // Quick but not overly forgiving XML mapping file processing.
+    bool mapTimezonesOpenTagFound = false;
+    bool mapTimezonesCloseTagFound = false;
+    std::size_t mapZonePos = std::string::npos;
+    std::size_t mapTimezonesPos = std::string::npos;
+    CONSTDATA char mapTimeZonesOpeningTag[] = { "<mapTimezones " };
+    CONSTDATA char mapZoneOpeningTag[] = { "<mapZone " };
+    CONSTDATA std::size_t mapZoneOpeningTagLen = sizeof(mapZoneOpeningTag) /
+                                                 sizeof(mapZoneOpeningTag[0]) - 1;
+    while (!mapTimezonesOpenTagFound)
+    {
+        std::getline(is, line);
+        ++line_num;
+        if (is.eof())
+        {
+            // If there is no mapTimezones tag is it an error?
+            // Perhaps if there are no mapZone mappings it might be ok for
+            // its parent mapTimezones element to be missing?
+            // We treat this as an error though on the assumption that if there
+            // really are no mappings we should still get a mapTimezones parent
+            // element but no mapZone elements inside. Assuming we must
+            // find something will hopefully at least catch more drastic formatting
+            // changes or errors than if we don't do this and assume nothing found.
+            error("Expected a mapTimezones opening tag.");
+        }
+        mapTimezonesPos = line.find(mapTimeZonesOpeningTag);
+        mapTimezonesOpenTagFound = (mapTimezonesPos != std::string::npos);
+    }
+
+    // NOTE: We could extract the version info that follows the opening
+    // mapTimezones tag and compare that to the version of other data we have.
+    // I would have expected them to be kept in synch but testing has shown
+    // it typically does not match anyway. So what's the point?
+    while (!mapTimezonesCloseTagFound)
+    {
+        std::ws(is);
+        std::getline(is, line);
+        ++line_num;
+        if (is.eof())
+            error("Expected a mapTimezones closing tag.");
+        if (line.empty())
+            continue;
+        mapZonePos = line.find(mapZoneOpeningTag);
+        if (mapZonePos != std::string::npos)
+        {
+            mapZonePos += mapZoneOpeningTagLen;
+            detail::timezone_mapping zm{};
+            std::size_t pos = read_attribute("other", zm.other, mapZonePos);
+            pos = read_attribute("territory", zm.territory, pos);
+            read_attribute("type", zm.type, pos);
+            mappings.push_back(std::move(zm));
+
+            continue;
+        }
+        mapTimezonesPos = line.find("</mapTimezones>");
+        mapTimezonesCloseTagFound = (mapTimezonesPos != std::string::npos);
+        if (!mapTimezonesCloseTagFound)
+        {
+            std::size_t commentPos = line.find("<!--");
+            if (commentPos == std::string::npos)
+                error("Unexpected mapping record found. A xml mapZone or comment "
+                      "attribute or mapTimezones closing tag was expected.");
+        }
+    }
+
+    is.close();
+    return mappings;
+}
+
+#endif  // _WIN32
+
+// Parsing helpers
+
+static
+unsigned
+parse_dow(std::istream& in)
+{
+    CONSTDATA char*const dow_names[] =
+        {"Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"};
+    auto s = parse3(in);
+    auto dow = std::find(std::begin(dow_names), std::end(dow_names), s) - dow_names;
+    if (dow >= std::end(dow_names) - std::begin(dow_names))
+        throw std::runtime_error("oops: bad dow name: " + s);
+    return static_cast<unsigned>(dow);
+}
+
+static
+std::chrono::seconds
+parse_unsigned_time(std::istream& in)
+{
+    using namespace std::chrono;
+    int x;
+    in >> x;
+    auto r = seconds{hours{x}};
+    if (!in.eof() && in.peek() == ':')
+    {
+        in.get();
+        in >> x;
+        r += minutes{x};
+        if (!in.eof() && in.peek() == ':')
+        {
+            in.get();
+            in >> x;
+            r += seconds{x};
+        }
+    }
+    return r;
+}
+
+static
+std::chrono::seconds
+parse_signed_time(std::istream& in)
+{
+    ws(in);
+    auto sign = 1;
+    if (in.peek() == '-')
+    {
+        sign = -1;
+        in.get();
+    }
+    else if (in.peek() == '+')
+        in.get();
+    return sign * parse_unsigned_time(in);
+}
+
+// MonthDayTime
+
+detail::MonthDayTime::MonthDayTime(local_seconds tp, tz timezone)
+    : zone_(timezone)
+{
+    using namespace date;
+    const auto dp = date::floor<days>(tp);
+    const auto hms = make_time(tp - dp);
+    const auto ymd = year_month_day(dp);
+    u = ymd.month() / ymd.day();
+    h_ = hms.hours();
+    m_ = hms.minutes();
+    s_ = hms.seconds();
+}
+
+detail::MonthDayTime::MonthDayTime(const date::month_day& md, tz timezone)
+    : zone_(timezone)
+{
+    u = md;
+}
+
+date::day
+detail::MonthDayTime::day() const
+{
+    switch (type_)
+    {
+    case month_day:
+        return u.month_day_.day();
+    case month_last_dow:
+        return date::day{31};
+    case lteq:
+    case gteq:
+        break;
+    }
+    return u.month_day_weekday_.month_day_.day();
+}
+
+date::month
+detail::MonthDayTime::month() const
+{
+    switch (type_)
+    {
+    case month_day:
+        return u.month_day_.month();
+    case month_last_dow:
+        return u.month_weekday_last_.month();
+    case lteq:
+    case gteq:
+        break;
+    }
+    return u.month_day_weekday_.month_day_.month();
+}
+
+int
+detail::MonthDayTime::compare(date::year y, const MonthDayTime& x, date::year yx,
+                      std::chrono::seconds offset, std::chrono::minutes prev_save) const
+{
+    if (zone_ != x.zone_)
+    {
+        auto dp0 = to_sys_days(y);
+        auto dp1 = x.to_sys_days(yx);
+        if (std::abs((dp0-dp1).count()) > 1)
+            return dp0 < dp1 ? -1 : 1;
+        if (zone_ == tz::local)
+        {
+            auto tp0 = to_time_point(y) - prev_save;
+            if (x.zone_ == tz::utc)
+                tp0 -= offset;
+            auto tp1 = x.to_time_point(yx);
+            return tp0 < tp1 ? -1 : tp0 == tp1 ? 0 : 1;
+        }
+        else if (zone_ == tz::standard)
+        {
+            auto tp0 = to_time_point(y);
+            auto tp1 = x.to_time_point(yx);
+            if (x.zone_ == tz::local)
+                tp1 -= prev_save;
+            else
+                tp0 -= offset;
+            return tp0 < tp1 ? -1 : tp0 == tp1 ? 0 : 1;
+        }
+        // zone_ == tz::utc
+        auto tp0 = to_time_point(y);
+        auto tp1 = x.to_time_point(yx);
+        if (x.zone_ == tz::local)
+            tp1 -= offset + prev_save;
+        else
+            tp1 -= offset;
+        return tp0 < tp1 ? -1 : tp0 == tp1 ? 0 : 1;
+    }
+    auto const t0 = to_time_point(y);
+    auto const t1 = x.to_time_point(yx);
+    return t0 < t1 ? -1 : t0 == t1 ? 0 : 1;
+}
+
+sys_seconds
+detail::MonthDayTime::to_sys(date::year y, std::chrono::seconds offset,
+                     std::chrono::seconds save) const
+{
+    using namespace date;
+    using namespace std::chrono;
+    auto until_utc = to_time_point(y);
+    if (zone_ == tz::standard)
+        until_utc -= offset;
+    else if (zone_ == tz::local)
+        until_utc -= offset + save;
+    return until_utc;
+}
+
+detail::MonthDayTime::U&
+detail::MonthDayTime::U::operator=(const date::month_day& x)
+{
+    month_day_ = x;
+    return *this;
+}
+
+detail::MonthDayTime::U&
+detail::MonthDayTime::U::operator=(const date::month_weekday_last& x)
+{
+    month_weekday_last_ = x;
+    return *this;
+}
+
+detail::MonthDayTime::U&
+detail::MonthDayTime::U::operator=(const pair& x)
+{
+    month_day_weekday_ = x;
+    return *this;
+}
+
+date::sys_days
+detail::MonthDayTime::to_sys_days(date::year y) const
+{
+    using namespace std::chrono;
+    using namespace date;
+    switch (type_)
+    {
+    case month_day:
+        return sys_days(y/u.month_day_);
+    case month_last_dow:
+        return sys_days(y/u.month_weekday_last_);
+    case lteq:
+        {
+            auto const x = y/u.month_day_weekday_.month_day_;
+            auto const wd1 = weekday(static_cast<sys_days>(x));
+            auto const wd0 = u.month_day_weekday_.weekday_;
+            return sys_days(x) - (wd1-wd0);
+        }
+    case gteq:
+        break;
+    }
+    auto const x = y/u.month_day_weekday_.month_day_;
+    auto const wd1 = u.month_day_weekday_.weekday_;
+    auto const wd0 = weekday(static_cast<sys_days>(x));
+    return sys_days(x) + (wd1-wd0);
+}
+
+sys_seconds
+detail::MonthDayTime::to_time_point(date::year y) const
+{
+    // Add seconds first to promote to largest rep early to prevent overflow
+    return to_sys_days(y) + s_ + h_ + m_;
+}
+
+void
+detail::MonthDayTime::canonicalize(date::year y)
+{
+    using namespace std::chrono;
+    using namespace date;
+    switch (type_)
+    {
+    case month_day:
+        return;
+    case month_last_dow:
+        {
+            auto const ymd = year_month_day(sys_days(y/u.month_weekday_last_));
+            u.month_day_ = ymd.month()/ymd.day();
+            type_ = month_day;
+            return;
+        }
+    case lteq:
+        {
+            auto const x = y/u.month_day_weekday_.month_day_;
+            auto const wd1 = weekday(static_cast<sys_days>(x));
+            auto const wd0 = u.month_day_weekday_.weekday_;
+            auto const ymd = year_month_day(sys_days(x) - (wd1-wd0));
+            u.month_day_ = ymd.month()/ymd.day();
+            type_ = month_day;
+            return;
+        }
+    case gteq:
+        {
+            auto const x = y/u.month_day_weekday_.month_day_;
+            auto const wd1 = u.month_day_weekday_.weekday_;
+            auto const wd0 = weekday(static_cast<sys_days>(x));
+            auto const ymd = year_month_day(sys_days(x) + (wd1-wd0));
+            u.month_day_ = ymd.month()/ymd.day();
+            type_ = month_day;
+            return;
+        }
+    }
+}
+
+std::istream&
+detail::operator>>(std::istream& is, MonthDayTime& x)
+{
+    using namespace date;
+    using namespace std::chrono;
+    assert(((std::ios::failbit | std::ios::badbit) & is.exceptions()) ==
+            (std::ios::failbit | std::ios::badbit));
+    x = MonthDayTime{};
+    if (!is.eof() && ws(is) && !is.eof() && is.peek() != '#')
+    {
+        auto m = parse_month(is);
+        if (!is.eof() && ws(is) && !is.eof() && is.peek() != '#')
+        {
+            if (is.peek() == 'l')
+            {
+                for (int i = 0; i < 4; ++i)
+                    is.get();
+                auto dow = parse_dow(is);
+                x.type_ = MonthDayTime::month_last_dow;
+                x.u = date::month(m)/weekday(dow)[last];
+            }
+            else if (std::isalpha(is.peek()))
+            {
+                auto dow = parse_dow(is);
+                char c{};
+                is >> c;
+                if (c == '<' || c == '>')
+                {
+                    char c2{};
+                    is >> c2;
+                    if (c2 != '=')
+                        throw std::runtime_error(std::string("bad operator: ") + c + c2);
+                    int d;
+                    is >> d;
+                    if (d < 1 || d > 31)
+                        throw std::runtime_error(std::string("bad operator: ") + c + c2
+                                 + std::to_string(d));
+                    x.type_ = c == '<' ? MonthDayTime::lteq : MonthDayTime::gteq;
+                    x.u = MonthDayTime::pair{ date::month(m) / d, date::weekday(dow) };
+                }
+                else
+                    throw std::runtime_error(std::string("bad operator: ") + c);
+            }
+            else  // if (std::isdigit(is.peek())
+            {
+                int d;
+                is >> d;
+                if (d < 1 || d > 31)
+                    throw std::runtime_error(std::string("day of month: ")
+                             + std::to_string(d));
+                x.type_ = MonthDayTime::month_day;
+                x.u = date::month(m)/d;
+            }
+            if (!is.eof() && ws(is) && !is.eof() && is.peek() != '#')
+            {
+                int t;
+                is >> t;
+                x.h_ = hours{t};
+                if (!is.eof() && is.peek() == ':')
+                {
+                    is.get();
+                    is >> t;
+                    x.m_ = minutes{t};
+                    if (!is.eof() && is.peek() == ':')
+                    {
+                        is.get();
+                        is >> t;
+                        x.s_ = seconds{t};
+                    }
+                }
+                if (!is.eof() && std::isalpha(is.peek()))
+                {
+                    char c;
+                    is >> c;
+                    switch (c)
+                    {
+                    case 's':
+                        x.zone_ = tz::standard;
+                        break;
+                    case 'u':
+                        x.zone_ = tz::utc;
+                        break;
+                    }
+                }
+            }
+        }
+        else
+        {
+            x.u = month{m}/1;
+        }
+    }
+    return is;
+}
+
+std::ostream&
+detail::operator<<(std::ostream& os, const MonthDayTime& x)
+{
+    switch (x.type_)
+    {
+    case MonthDayTime::month_day:
+        os << x.u.month_day_ << "                  ";
+        break;
+    case MonthDayTime::month_last_dow:
+        os << x.u.month_weekday_last_ << "           ";
+        break;
+    case MonthDayTime::lteq:
+        os << x.u.month_day_weekday_.weekday_ << " on or before "
+           << x.u.month_day_weekday_.month_day_ << "  ";
+        break;
+    case MonthDayTime::gteq:
+        if ((static_cast<unsigned>(x.day()) - 1) % 7 == 0)
+        {
+            os << (x.u.month_day_weekday_.month_day_.month() /
+                   x.u.month_day_weekday_.weekday_[
+                       (static_cast<unsigned>(x.day()) - 1)/7+1]) << "              ";
+        }
+        else
+        {
+            os << x.u.month_day_weekday_.weekday_ << " on or after "
+               << x.u.month_day_weekday_.month_day_ << "  ";
+        }
+        break;
+    }
+    os << date::make_time(x.s_ + x.h_ + x.m_);
+    if (x.zone_ == tz::utc)
+        os << "UTC   ";
+    else if (x.zone_ == tz::standard)
+        os << "STD   ";
+    else
+        os << "      ";
+    return os;
+}
+
+// Rule
+
+detail::Rule::Rule(const std::string& s)
+{
+    try
+    {
+        using namespace date;
+        using namespace std::chrono;
+        std::istringstream in(s);
+        in.exceptions(std::ios::failbit | std::ios::badbit);
+        std::string word;
+        in >> word >> name_;
+        int x;
+        ws(in);
+        if (std::isalpha(in.peek()))
+        {
+            in >> word;
+            if (word == "min")
+            {
+                starting_year_ = year::min();
+            }
+            else
+                throw std::runtime_error("Didn't find expected word: " + word);
+        }
+        else
+        {
+            in >> x;
+            starting_year_ = year{x};
+        }
+        std::ws(in);
+        if (std::isalpha(in.peek()))
+        {
+            in >> word;
+            if (word == "only")
+            {
+                ending_year_ = starting_year_;
+            }
+            else if (word == "max")
+            {
+                ending_year_ = year::max();
+            }
+            else
+                throw std::runtime_error("Didn't find expected word: " + word);
+        }
+        else
+        {
+            in >> x;
+            ending_year_ = year{x};
+        }
+        in >> word;  // TYPE (always "-")
+        assert(word == "-");
+        in >> starting_at_;
+        save_ = duration_cast<minutes>(parse_signed_time(in));
+        in >> abbrev_;
+        if (abbrev_ == "-")
+            abbrev_.clear();
+        assert(hours{-1} <= save_ && save_ <= hours{2});
+    }
+    catch (...)
+    {
+        std::cerr << s << '\n';
+        std::cerr << *this << '\n';
+        throw;
+    }
+}
+
+detail::Rule::Rule(const Rule& r, date::year starting_year, date::year ending_year)
+    : name_(r.name_)
+    , starting_year_(starting_year)
+    , ending_year_(ending_year)
+    , starting_at_(r.starting_at_)
+    , save_(r.save_)
+    , abbrev_(r.abbrev_)
+{
+}
+
+bool
+detail::operator==(const Rule& x, const Rule& y)
+{
+    if (std::tie(x.name_, x.save_, x.starting_year_, x.ending_year_) ==
+        std::tie(y.name_, y.save_, y.starting_year_, y.ending_year_))
+        return x.month() == y.month() && x.day() == y.day();
+    return false;
+}
+
+bool
+detail::operator<(const Rule& x, const Rule& y)
+{
+    using namespace std::chrono;
+    auto const xm = x.month();
+    auto const ym = y.month();
+    if (std::tie(x.name_, x.starting_year_, xm, x.ending_year_) <
+        std::tie(y.name_, y.starting_year_, ym, y.ending_year_))
+        return true;
+    if (std::tie(x.name_, x.starting_year_, xm, x.ending_year_) >
+        std::tie(y.name_, y.starting_year_, ym, y.ending_year_))
+        return false;
+    return x.day() < y.day();
+}
+
+bool
+detail::operator==(const Rule& x, const date::year& y)
+{
+    return x.starting_year_ <= y && y <= x.ending_year_;
+}
+
+bool
+detail::operator<(const Rule& x, const date::year& y)
+{
+    return x.ending_year_ < y;
+}
+
+bool
+detail::operator==(const date::year& x, const Rule& y)
+{
+    return y.starting_year_ <= x && x <= y.ending_year_;
+}
+
+bool
+detail::operator<(const date::year& x, const Rule& y)
+{
+    return x < y.starting_year_;
+}
+
+bool
+detail::operator==(const Rule& x, const std::string& y)
+{
+    return x.name() == y;
+}
+
+bool
+detail::operator<(const Rule& x, const std::string& y)
+{
+    return x.name() < y;
+}
+
+bool
+detail::operator==(const std::string& x, const Rule& y)
+{
+    return y.name() == x;
+}
+
+bool
+detail::operator<(const std::string& x, const Rule& y)
+{
+    return x < y.name();
+}
+
+std::ostream&
+detail::operator<<(std::ostream& os, const Rule& r)
+{
+    using namespace date;
+    using namespace std::chrono;
+    detail::save_ostream<char> _(os);
+    os.fill(' ');
+    os.flags(std::ios::dec | std::ios::left);
+    os.width(15);
+    os << r.name_;
+    os << r.starting_year_ << "    " << r.ending_year_ << "    ";
+    os << r.starting_at_;
+    if (r.save_ >= minutes{0})
+        os << ' ';
+    os << date::make_time(r.save_) << "   ";
+    os << r.abbrev_;
+    return os;
+}
+
+date::day
+detail::Rule::day() const
+{
+    return starting_at_.day();
+}
+
+date::month
+detail::Rule::month() const
+{
+    return starting_at_.month();
+}
+
+struct find_rule_by_name
+{
+    bool operator()(const Rule& x, const std::string& nm) const
+    {
+        return x.name() < nm;
+    }
+
+    bool operator()(const std::string& nm, const Rule& x) const
+    {
+        return nm < x.name();
+    }
+};
+
+bool
+detail::Rule::overlaps(const Rule& x, const Rule& y)
+{
+    // assume x.starting_year_ <= y.starting_year_;
+    if (!(x.starting_year_ <= y.starting_year_))
+    {
+        std::cerr << x << '\n';
+        std::cerr << y << '\n';
+        assert(x.starting_year_ <= y.starting_year_);
+    }
+    if (y.starting_year_ > x.ending_year_)
+        return false;
+    return !(x.starting_year_ == y.starting_year_ && x.ending_year_ == y.ending_year_);
+}
+
+void
+detail::Rule::split(std::vector<Rule>& rules, std::size_t i, std::size_t k, std::size_t& e)
+{
+    using namespace date;
+    using difference_type = std::vector<Rule>::iterator::difference_type;
+    // rules[i].starting_year_ <= rules[k].starting_year_ &&
+    //     rules[i].ending_year_ >= rules[k].starting_year_ &&
+    //     (rules[i].starting_year_ != rules[k].starting_year_ ||
+    //      rules[i].ending_year_ != rules[k].ending_year_)
+    assert(rules[i].starting_year_ <= rules[k].starting_year_ &&
+           rules[i].ending_year_ >= rules[k].starting_year_ &&
+           (rules[i].starting_year_ != rules[k].starting_year_ ||
+            rules[i].ending_year_ != rules[k].ending_year_));
+    if (rules[i].starting_year_ == rules[k].starting_year_)
+    {
+        if (rules[k].ending_year_ < rules[i].ending_year_)
+        {
+            rules.insert(rules.begin() + static_cast<difference_type>(k+1),
+                         Rule(rules[i], rules[k].ending_year_ + years{1},
+                              std::move(rules[i].ending_year_)));
+            ++e;
+            rules[i].ending_year_ = rules[k].ending_year_;
+        }
+        else  // rules[k].ending_year_ > rules[i].ending_year_
+        {
+            rules.insert(rules.begin() + static_cast<difference_type>(k+1),
+                         Rule(rules[k], rules[i].ending_year_ + years{1},
+                              std::move(rules[k].ending_year_)));
+            ++e;
+            rules[k].ending_year_ = rules[i].ending_year_;
+        }
+    }
+    else  // rules[i].starting_year_ < rules[k].starting_year_
+    {
+        if (rules[k].ending_year_ < rules[i].ending_year_)
+        {
+            rules.insert(rules.begin() + static_cast<difference_type>(k),
+                         Rule(rules[i], rules[k].starting_year_, rules[k].ending_year_));
+            ++k;
+            rules.insert(rules.begin() + static_cast<difference_type>(k+1),
+                         Rule(rules[i], rules[k].ending_year_ + years{1},
+                              std::move(rules[i].ending_year_)));
+            rules[i].ending_year_ = rules[k].starting_year_ - years{1};
+            e += 2;
+        }
+        else if (rules[k].ending_year_ > rules[i].ending_year_)
+        {
+            rules.insert(rules.begin() + static_cast<difference_type>(k),
+                         Rule(rules[i], rules[k].starting_year_, rules[i].ending_year_));
+            ++k;
+            rules.insert(rules.begin() + static_cast<difference_type>(k+1),
+                         Rule(rules[k], rules[i].ending_year_ + years{1},
+                         std::move(rules[k].ending_year_)));
+            e += 2;
+            rules[k].ending_year_ = std::move(rules[i].ending_year_);
+            rules[i].ending_year_ = rules[k].starting_year_ - years{1};
+        }
+        else  // rules[k].ending_year_ == rules[i].ending_year_
+        {
+            rules.insert(rules.begin() + static_cast<difference_type>(k),
+                         Rule(rules[i], rules[k].starting_year_,
+                         std::move(rules[i].ending_year_)));
+            ++k;
+            ++e;
+            rules[i].ending_year_ = rules[k].starting_year_ - years{1};
+        }
+    }
+}
+
+void
+detail::Rule::split_overlaps(std::vector<Rule>& rules, std::size_t i, std::size_t& e)
+{
+    using difference_type = std::vector<Rule>::iterator::difference_type;
+    auto j = i;
+    for (; i + 1 < e; ++i)
+    {
+        for (auto k = i + 1; k < e; ++k)
+        {
+            if (overlaps(rules[i], rules[k]))
+            {
+                split(rules, i, k, e);
+                std::sort(rules.begin() + static_cast<difference_type>(i),
+                          rules.begin() + static_cast<difference_type>(e));
+            }
+        }
+    }
+    for (; j < e; ++j)
+    {
+        if (rules[j].starting_year() == rules[j].ending_year())
+            rules[j].starting_at_.canonicalize(rules[j].starting_year());
+    }
+}
+
+void
+detail::Rule::split_overlaps(std::vector<Rule>& rules)
+{
+    using difference_type = std::vector<Rule>::iterator::difference_type;
+    for (std::size_t i = 0; i < rules.size();)
+    {
+        auto e = static_cast<std::size_t>(std::upper_bound(
+            rules.cbegin()+static_cast<difference_type>(i), rules.cend(), rules[i].name(),
+            [](const std::string& nm, const Rule& x)
+            {
+                return nm < x.name();
+            }) - rules.cbegin());
+        split_overlaps(rules, i, e);
+        auto first_rule = rules.begin() + static_cast<difference_type>(i);
+        auto last_rule = rules.begin() + static_cast<difference_type>(e);
+        auto t = std::lower_bound(first_rule, last_rule, min_year);
+        if (t > first_rule+1)
+        {
+            if (t == last_rule || t->starting_year() >= min_year)
+                --t;
+            auto d = static_cast<std::size_t>(t - first_rule);
+            rules.erase(first_rule, t);
+            e -= d;
+        }
+        first_rule = rules.begin() + static_cast<difference_type>(i);
+        last_rule = rules.begin() + static_cast<difference_type>(e);
+        t = std::upper_bound(first_rule, last_rule, max_year);
+        if (t != last_rule)
+        {
+            auto d = static_cast<std::size_t>(last_rule - t);
+            rules.erase(t, last_rule);
+            e -= d;
+        }
+        i = e;
+    }
+    rules.shrink_to_fit();
+}
+
+// Find the rule that comes chronologically before Rule r.  For multi-year rules,
+// y specifies which rules in r.  For single year rules, y is assumed to be equal
+// to the year specified by r.
+// Returns a pointer to the chronologically previous rule, and the year within
+// that rule.  If there is no previous rule, returns nullptr and year::min().
+// Preconditions:
+//     r->starting_year() <= y && y <= r->ending_year()
+static
+std::pair<const Rule*, date::year>
+find_previous_rule(const Rule* r, date::year y)
+{
+    using namespace date;
+    auto const& rules = get_tzdb().rules;
+    if (y == r->starting_year())
+    {
+        if (r == &rules.front() || r->name() != r[-1].name())
+            std::terminate();  // never called with first rule
+        --r;
+        if (y == r->starting_year())
+            return {r, y};
+        return {r, r->ending_year()};
+    }
+    if (r == &rules.front() || r->name() != r[-1].name() ||
+        r[-1].starting_year() < r->starting_year())
+    {
+        while (r < &rules.back() && r->name() == r[1].name() &&
+               r->starting_year() == r[1].starting_year())
+            ++r;
+        return {r, --y};
+    }
+    --r;
+    return {r, y};
+}
+
+// Find the rule that comes chronologically after Rule r.  For multi-year rules,
+// y specifies which rules in r.  For single year rules, y is assumed to be equal
+// to the year specified by r.
+// Returns a pointer to the chronologically next rule, and the year within
+// that rule.  If there is no next rule, return a pointer to a defaulted rule
+// and y+1.
+// Preconditions:
+//     first <= r && r < last && r->starting_year() <= y && y <= r->ending_year()
+//     [first, last) all have the same name
+static
+std::pair<const Rule*, date::year>
+find_next_rule(const Rule* first_rule, const Rule* last_rule, const Rule* r, date::year y)
+{
+    using namespace date;
+    if (y == r->ending_year())
+    {
+        if (r == last_rule-1)
+            return {nullptr, year::max()};
+        ++r;
+        if (y == r->ending_year())
+            return {r, y};
+        return {r, r->starting_year()};
+    }
+    if (r == last_rule-1 || r->ending_year() < r[1].ending_year())
+    {
+        while (r > first_rule && r->starting_year() == r[-1].starting_year())
+            --r;
+        return {r, ++y};
+    }
+    ++r;
+    return {r, y};
+}
+
+// Find the rule that comes chronologically after Rule r.  For multi-year rules,
+// y specifies which rules in r.  For single year rules, y is assumed to be equal
+// to the year specified by r.
+// Returns a pointer to the chronologically next rule, and the year within
+// that rule.  If there is no next rule, return nullptr and year::max().
+// Preconditions:
+//     r->starting_year() <= y && y <= r->ending_year()
+static
+std::pair<const Rule*, date::year>
+find_next_rule(const Rule* r, date::year y)
+{
+    using namespace date;
+    auto const& rules = get_tzdb().rules;
+    if (y == r->ending_year())
+    {
+        if (r == &rules.back() || r->name() != r[1].name())
+            return {nullptr, year::max()};
+        ++r;
+        if (y == r->ending_year())
+            return {r, y};
+        return {r, r->starting_year()};
+    }
+    if (r == &rules.back() || r->name() != r[1].name() ||
+        r->ending_year() < r[1].ending_year())
+    {
+        while (r > &rules.front() && r->name() == r[-1].name() &&
+               r->starting_year() == r[-1].starting_year())
+            --r;
+        return {r, ++y};
+    }
+    ++r;
+    return {r, y};
+}
+
+static
+const Rule*
+find_first_std_rule(const std::pair<const Rule*, const Rule*>& eqr)
+{
+    auto r = eqr.first;
+    auto ry = r->starting_year();
+    while (r->save() != std::chrono::minutes{0})
+    {
+        std::tie(r, ry) = find_next_rule(eqr.first, eqr.second, r, ry);
+        if (r == nullptr)
+            throw std::runtime_error("Could not find standard offset in rule "
+                                     + eqr.first->name());
+    }
+    return r;
+}
+
+static
+std::pair<const Rule*, date::year>
+find_rule_for_zone(const std::pair<const Rule*, const Rule*>& eqr,
+                   const date::year& y, const std::chrono::seconds& offset,
+                   const MonthDayTime& mdt)
+{
+    assert(eqr.first != nullptr);
+    assert(eqr.second != nullptr);
+
+    using namespace std::chrono;
+    using namespace date;
+    auto r = eqr.first;
+    auto ry = r->starting_year();
+    auto prev_save = minutes{0};
+    auto prev_year = year::min();
+    const Rule* prev_rule = nullptr;
+    while (r != nullptr)
+    {
+        if (mdt.compare(y, r->mdt(), ry, offset, prev_save) <= 0)
+            break;
+        prev_rule = r;
+        prev_year = ry;
+        prev_save = prev_rule->save();
+        std::tie(r, ry) = find_next_rule(eqr.first, eqr.second, r, ry);
+    }
+    return {prev_rule, prev_year};
+}
+
+static
+std::pair<const Rule*, date::year>
+find_rule_for_zone(const std::pair<const Rule*, const Rule*>& eqr,
+                   const sys_seconds& tp_utc,
+                   const local_seconds& tp_std,
+                   const local_seconds& tp_loc)
+{
+    using namespace std::chrono;
+    using namespace date;
+    auto r = eqr.first;
+    auto ry = r->starting_year();
+    auto prev_save = minutes{0};
+    auto prev_year = year::min();
+    const Rule* prev_rule = nullptr;
+    while (r != nullptr)
+    {
+        bool found = false;
+        switch (r->mdt().zone())
+        {
+        case tz::utc:
+            found = tp_utc < r->mdt().to_time_point(ry);
+            break;
+        case tz::standard:
+            found = sys_seconds{tp_std.time_since_epoch()} < r->mdt().to_time_point(ry);
+            break;
+        case tz::local:
+            found = sys_seconds{tp_loc.time_since_epoch()} < r->mdt().to_time_point(ry);
+            break;
+        }
+        if (found)
+            break;
+        prev_rule = r;
+        prev_year = ry;
+        prev_save = prev_rule->save();
+        std::tie(r, ry) = find_next_rule(eqr.first, eqr.second, r, ry);
+    }
+    return {prev_rule, prev_year};
+}
+
+static
+sys_info
+find_rule(const std::pair<const Rule*, date::year>& first_rule,
+          const std::pair<const Rule*, date::year>& last_rule,
+          const date::year& y, const std::chrono::seconds& offset,
+          const MonthDayTime& mdt, const std::chrono::minutes& initial_save,
+          const std::string& initial_abbrev)
+{
+    using namespace std::chrono;
+    using namespace date;
+    auto r = first_rule.first;
+    auto ry = first_rule.second;
+    sys_info x{sys_days(year::min()/min_day), sys_days(year::max()/max_day),
+               seconds{0}, initial_save, initial_abbrev};
+    while (r != nullptr)
+    {
+        auto tr = r->mdt().to_sys(ry, offset, x.save);
+        auto tx = mdt.to_sys(y, offset, x.save);
+        // Find last rule where tx >= tr
+        if (tx <= tr || (r == last_rule.first && ry == last_rule.second))
+        {
+            if (tx < tr && r == first_rule.first && ry == first_rule.second)
+            {
+                x.end = r->mdt().to_sys(ry, offset, x.save);
+                break;
+            }
+            if (tx < tr)
+            {
+                std::tie(r, ry) = find_previous_rule(r, ry);  // can't return nullptr for r
+                assert(r != nullptr);
+            }
+            // r != nullptr && tx >= tr (if tr were to be recomputed)
+            auto prev_save = initial_save;
+            if (!(r == first_rule.first && ry == first_rule.second))
+                prev_save = find_previous_rule(r, ry).first->save();
+            x.begin = r->mdt().to_sys(ry, offset, prev_save);
+            x.save = r->save();
+            x.abbrev = r->abbrev();
+            if (!(r == last_rule.first && ry == last_rule.second))
+            {
+                std::tie(r, ry) = find_next_rule(r, ry);  // can't return nullptr for r
+                assert(r != nullptr);
+                x.end = r->mdt().to_sys(ry, offset, x.save);
+            }
+            else
+                x.end = sys_days(year::max()/max_day);
+            break;
+        }
+        x.save = r->save();
+        std::tie(r, ry) = find_next_rule(r, ry);  // Can't return nullptr for r
+        assert(r != nullptr);
+    }
+    return x;
+}
+
+// zonelet
+
+detail::zonelet::~zonelet()
+{
+#if !defined(_MSC_VER) || (_MSC_VER >= 1900)
+    using minutes = std::chrono::minutes;
+    using string = std::string;
+    if (tag_ == has_save)
+        u.save_.~minutes();
+    else
+        u.rule_.~string();
+#endif
+}
+
+detail::zonelet::zonelet()
+{
+#if !defined(_MSC_VER) || (_MSC_VER >= 1900)
+    ::new(&u.rule_) std::string();
+#endif
+}
+
+detail::zonelet::zonelet(const zonelet& i)
+    : gmtoff_(i.gmtoff_)
+    , tag_(i.tag_)
+    , format_(i.format_)
+    , until_year_(i.until_year_)
+    , until_date_(i.until_date_)
+    , until_utc_(i.until_utc_)
+    , until_std_(i.until_std_)
+    , until_loc_(i.until_loc_)
+    , initial_save_(i.initial_save_)
+    , initial_abbrev_(i.initial_abbrev_)
+    , first_rule_(i.first_rule_)
+    , last_rule_(i.last_rule_)
+{
+#if !defined(_MSC_VER) || (_MSC_VER >= 1900)
+    if (tag_ == has_save)
+        ::new(&u.save_) std::chrono::minutes(i.u.save_);
+    else
+        ::new(&u.rule_) std::string(i.u.rule_);
+#else
+    if (tag_ == has_save)
+        u.save_ = i.u.save_;
+    else
+        u.rule_ = i.u.rule_;
+#endif
+}
+
+#endif  // !USE_OS_TZDB
+
+// time_zone
+
+#if USE_OS_TZDB
+
+time_zone::time_zone(const std::string& s, detail::undocumented)
+    : name_(s)
+    , adjusted_(new std::once_flag{})
+{
+}
+
+enum class endian
+{
+    native = __BYTE_ORDER__,
+    little = __ORDER_LITTLE_ENDIAN__,
+    big    = __ORDER_BIG_ENDIAN__
+};
+
+static
+inline
+std::uint32_t
+reverse_bytes(std::uint32_t i)
+{
+    return
+        (i & 0xff000000u) >> 24 |
+        (i & 0x00ff0000u) >> 8 |
+        (i & 0x0000ff00u) << 8 |
+        (i & 0x000000ffu) << 24;
+}
+
+static
+inline
+std::uint64_t
+reverse_bytes(std::uint64_t i)
+{
+    return
+        (i & 0xff00000000000000ull) >> 56 |
+        (i & 0x00ff000000000000ull) >> 40 |
+        (i & 0x0000ff0000000000ull) >> 24 |
+        (i & 0x000000ff00000000ull) >> 8 |
+        (i & 0x00000000ff000000ull) << 8 |
+        (i & 0x0000000000ff0000ull) << 24 |
+        (i & 0x000000000000ff00ull) << 40 |
+        (i & 0x00000000000000ffull) << 56;
+}
+
+template <class T>
+static
+inline
+void
+maybe_reverse_bytes(T&, std::false_type)
+{
+}
+
+static
+inline
+void
+maybe_reverse_bytes(std::int32_t& t, std::true_type)
+{
+    t = static_cast<std::int32_t>(reverse_bytes(static_cast<std::uint32_t>(t)));
+}
+
+static
+inline
+void
+maybe_reverse_bytes(std::int64_t& t, std::true_type)
+{
+    t = static_cast<std::int64_t>(reverse_bytes(static_cast<std::uint64_t>(t)));
+}
+
+template <class T>
+static
+inline
+void
+maybe_reverse_bytes(T& t)
+{
+    maybe_reverse_bytes(t, std::integral_constant<bool,
+                                                  endian::native == endian::little>{});
+}
+
+static
+void
+load_header(std::istream& inf)
+{
+    // Read TZif
+    auto t = inf.get();
+    auto z = inf.get();
+    auto i = inf.get();
+    auto f = inf.get();
+#ifndef NDEBUG
+    assert(t == 'T');
+    assert(z == 'Z');
+    assert(i == 'i');
+    assert(f == 'f');
+#else
+    (void)t;
+    (void)z;
+    (void)i;
+    (void)f;
+#endif
+}
+
+static
+unsigned char
+load_version(std::istream& inf)
+{
+    // Read version
+    auto v = inf.get();
+    assert(v != EOF);
+    return static_cast<unsigned char>(v);
+}
+
+static
+void
+skip_reserve(std::istream& inf)
+{
+    inf.ignore(15);
+}
+
+static
+void
+load_counts(std::istream& inf,
+            std::int32_t& tzh_ttisgmtcnt, std::int32_t& tzh_ttisstdcnt,
+            std::int32_t& tzh_leapcnt,    std::int32_t& tzh_timecnt,
+            std::int32_t& tzh_typecnt,    std::int32_t& tzh_charcnt)
+{
+    // Read counts;
+    inf.read(reinterpret_cast<char*>(&tzh_ttisgmtcnt), 4);
+    maybe_reverse_bytes(tzh_ttisgmtcnt);
+    inf.read(reinterpret_cast<char*>(&tzh_ttisstdcnt), 4);
+    maybe_reverse_bytes(tzh_ttisstdcnt);
+    inf.read(reinterpret_cast<char*>(&tzh_leapcnt), 4);
+    maybe_reverse_bytes(tzh_leapcnt);
+    inf.read(reinterpret_cast<char*>(&tzh_timecnt), 4);
+    maybe_reverse_bytes(tzh_timecnt);
+    inf.read(reinterpret_cast<char*>(&tzh_typecnt), 4);
+    maybe_reverse_bytes(tzh_typecnt);
+    inf.read(reinterpret_cast<char*>(&tzh_charcnt), 4);
+    maybe_reverse_bytes(tzh_charcnt);
+}
+
+template <class TimeType>
+static
+std::vector<detail::transition>
+load_transitions(std::istream& inf, std::int32_t tzh_timecnt)
+{
+    // Read transitions
+    using namespace std::chrono;
+    std::vector<detail::transition> transitions;
+    transitions.reserve(static_cast<unsigned>(tzh_timecnt));
+    for (std::int32_t i = 0; i < tzh_timecnt; ++i)
+    {
+        TimeType t;
+        inf.read(reinterpret_cast<char*>(&t), sizeof(t));
+        maybe_reverse_bytes(t);
+        transitions.emplace_back(sys_seconds{seconds{t}});
+        if (transitions.back().timepoint < min_seconds)
+            transitions.back().timepoint = min_seconds;
+    }
+    return transitions;
+}
+
+static
+std::vector<std::uint8_t>
+load_indices(std::istream& inf, std::int32_t tzh_timecnt)
+{
+    // Read indices
+    std::vector<std::uint8_t> indices;
+    indices.reserve(static_cast<unsigned>(tzh_timecnt));
+    for (std::int32_t i = 0; i < tzh_timecnt; ++i)
+    {
+        std::uint8_t t;
+        inf.read(reinterpret_cast<char*>(&t), sizeof(t));
+        indices.emplace_back(t);
+    }
+    return indices;
+}
+
+static
+std::vector<ttinfo>
+load_ttinfo(std::istream& inf, std::int32_t tzh_typecnt)
+{
+    // Read ttinfo
+    std::vector<ttinfo> ttinfos;
+    ttinfos.reserve(static_cast<unsigned>(tzh_typecnt));
+    for (std::int32_t i = 0; i < tzh_typecnt; ++i)
+    {
+        ttinfo t;
+        inf.read(reinterpret_cast<char*>(&t), 6);
+        maybe_reverse_bytes(t.tt_gmtoff);
+        ttinfos.emplace_back(t);
+    }
+    return ttinfos;
+}
+
+static
+std::string
+load_abbreviations(std::istream& inf, std::int32_t tzh_charcnt)
+{
+    // Read abbreviations
+    std::string abbrev;
+    abbrev.resize(static_cast<unsigned>(tzh_charcnt), '\0');
+    inf.read(&abbrev[0], tzh_charcnt);
+    return abbrev;
+}
+
+#if !MISSING_LEAP_SECONDS
+
+template <class TimeType>
+static
+std::vector<leap_second>
+load_leaps(std::istream& inf, std::int32_t tzh_leapcnt)
+{
+    // Read tzh_leapcnt pairs
+    using namespace std::chrono;
+    std::vector<leap_second> leap_seconds;
+    leap_seconds.reserve(static_cast<std::size_t>(tzh_leapcnt));
+    for (std::int32_t i = 0; i < tzh_leapcnt; ++i)
+    {
+        TimeType     t0;
+        std::int32_t t1;
+        inf.read(reinterpret_cast<char*>(&t0), sizeof(t0));
+        inf.read(reinterpret_cast<char*>(&t1), sizeof(t1));
+        maybe_reverse_bytes(t0);
+        maybe_reverse_bytes(t1);
+        leap_seconds.emplace_back(sys_seconds{seconds{t0 - (t1-1)}},
+                                  detail::undocumented{});
+    }
+    return leap_seconds;
+}
+
+template <class TimeType>
+static
+std::vector<leap_second>
+load_leap_data(std::istream& inf,
+               std::int32_t tzh_leapcnt, std::int32_t tzh_timecnt,
+               std::int32_t tzh_typecnt, std::int32_t tzh_charcnt)
+{
+    inf.ignore(tzh_timecnt*static_cast<std::int32_t>(sizeof(TimeType)) + tzh_timecnt +
+               tzh_typecnt*6 + tzh_charcnt);
+    return load_leaps<TimeType>(inf, tzh_leapcnt);
+}
+
+static
+std::vector<leap_second>
+load_just_leaps(std::istream& inf)
+{
+    // Read tzh_leapcnt pairs
+    using namespace std::chrono;
+    load_header(inf);
+    auto v = load_version(inf);
+    std::int32_t tzh_ttisgmtcnt, tzh_ttisstdcnt, tzh_leapcnt,
+                 tzh_timecnt,    tzh_typecnt,    tzh_charcnt;
+    skip_reserve(inf);
+    load_counts(inf, tzh_ttisgmtcnt, tzh_ttisstdcnt, tzh_leapcnt,
+                     tzh_timecnt,    tzh_typecnt,    tzh_charcnt);
+    if (v == 0)
+        return load_leap_data<int32_t>(inf, tzh_leapcnt, tzh_timecnt, tzh_typecnt,
+                                       tzh_charcnt);
+#if !defined(NDEBUG)
+    inf.ignore((4+1)*tzh_timecnt + 6*tzh_typecnt + tzh_charcnt + 8*tzh_leapcnt +
+               tzh_ttisstdcnt + tzh_ttisgmtcnt);
+    load_header(inf);
+    auto v2 = load_version(inf);
+    assert(v == v2);
+    skip_reserve(inf);
+#else  // defined(NDEBUG)
+    inf.ignore((4+1)*tzh_timecnt + 6*tzh_typecnt + tzh_charcnt + 8*tzh_leapcnt +
+               tzh_ttisstdcnt + tzh_ttisgmtcnt + (4+1+15));
+#endif  // defined(NDEBUG)
+    load_counts(inf, tzh_ttisgmtcnt, tzh_ttisstdcnt, tzh_leapcnt,
+                     tzh_timecnt,    tzh_typecnt,    tzh_charcnt);
+    return load_leap_data<int64_t>(inf, tzh_leapcnt, tzh_timecnt, tzh_typecnt,
+                                   tzh_charcnt);
+}
+
+#endif  // !MISSING_LEAP_SECONDS
+
+template <class TimeType>
+void
+time_zone::load_data(std::istream& inf,
+                     std::int32_t tzh_leapcnt, std::int32_t tzh_timecnt,
+                     std::int32_t tzh_typecnt, std::int32_t tzh_charcnt)
+{
+    using namespace std::chrono;
+    transitions_ = load_transitions<TimeType>(inf, tzh_timecnt);
+    auto indices = load_indices(inf, tzh_timecnt);
+    auto infos = load_ttinfo(inf, tzh_typecnt);
+    auto abbrev = load_abbreviations(inf, tzh_charcnt);
+#if !MISSING_LEAP_SECONDS
+    auto& leap_seconds = get_tzdb_list().front().leap_seconds;
+    if (leap_seconds.empty() && tzh_leapcnt > 0)
+        leap_seconds = load_leaps<TimeType>(inf, tzh_leapcnt);
+#endif
+    ttinfos_.reserve(infos.size());
+    for (auto& info : infos)
+    {
+        ttinfos_.push_back({seconds{info.tt_gmtoff},
+                            abbrev.c_str() + info.tt_abbrind,
+                            info.tt_isdst != 0});
+    }
+    auto i = 0u;
+    if (transitions_.empty() || transitions_.front().timepoint != min_seconds)
+    {
+        transitions_.emplace(transitions_.begin(), min_seconds);
+        auto tf = std::find_if(ttinfos_.begin(), ttinfos_.end(),
+                               [](const expanded_ttinfo& ti)
+                                   {return ti.is_dst == 0;});
+        if (tf == ttinfos_.end())
+            tf = ttinfos_.begin();
+        transitions_[i].info = &*tf;
+        ++i;
+    }
+    for (auto j = 0u; i < transitions_.size(); ++i, ++j)
+        transitions_[i].info = ttinfos_.data() + indices[j];
+}
+
+void
+time_zone::init_impl()
+{
+    using namespace std;
+    using namespace std::chrono;
+    auto name = get_tz_dir() + ('/' + name_);
+    std::ifstream inf(name);
+    if (!inf.is_open())
+        throw std::runtime_error{"Unable to open " + name};
+    inf.exceptions(std::ios::failbit | std::ios::badbit);
+    load_header(inf);
+    auto v = load_version(inf);
+    std::int32_t tzh_ttisgmtcnt, tzh_ttisstdcnt, tzh_leapcnt,
+                 tzh_timecnt,    tzh_typecnt,    tzh_charcnt;
+    skip_reserve(inf);
+    load_counts(inf, tzh_ttisgmtcnt, tzh_ttisstdcnt, tzh_leapcnt,
+                     tzh_timecnt,    tzh_typecnt,    tzh_charcnt);
+    if (v == 0)
+    {
+        load_data<int32_t>(inf, tzh_leapcnt, tzh_timecnt, tzh_typecnt, tzh_charcnt);
+    }
+    else
+    {
+#if !defined(NDEBUG)
+        inf.ignore((4+1)*tzh_timecnt + 6*tzh_typecnt + tzh_charcnt + 8*tzh_leapcnt +
+                   tzh_ttisstdcnt + tzh_ttisgmtcnt);
+        load_header(inf);
+        auto v2 = load_version(inf);
+        assert(v == v2);
+        skip_reserve(inf);
+#else  // defined(NDEBUG)
+        inf.ignore((4+1)*tzh_timecnt + 6*tzh_typecnt + tzh_charcnt + 8*tzh_leapcnt +
+                   tzh_ttisstdcnt + tzh_ttisgmtcnt + (4+1+15));
+#endif  // defined(NDEBUG)
+        load_counts(inf, tzh_ttisgmtcnt, tzh_ttisstdcnt, tzh_leapcnt,
+                         tzh_timecnt,    tzh_typecnt,    tzh_charcnt);
+        load_data<int64_t>(inf, tzh_leapcnt, tzh_timecnt, tzh_typecnt, tzh_charcnt);
+    }
+#if !MISSING_LEAP_SECONDS
+    if (tzh_leapcnt > 0)
+    {
+        auto& leap_seconds = get_tzdb_list().front().leap_seconds;
+        auto itr = leap_seconds.begin();
+        auto l = itr->date();
+        seconds leap_count{0};
+        for (auto t = std::upper_bound(transitions_.begin(), transitions_.end(), l,
+                                       [](const sys_seconds& x, const transition& ct)
+                                       {
+                                           return x < ct.timepoint;
+                                       });
+                  t != transitions_.end(); ++t)
+        {
+            while (t->timepoint >= l)
+            {
+                ++leap_count;
+                if (++itr == leap_seconds.end())
+                    l = sys_days(max_year/max_day);
+                else
+                    l = itr->date() + leap_count;
+            }
+            t->timepoint -= leap_count;
+        }
+    }
+#endif  // !MISSING_LEAP_SECONDS
+    auto b = transitions_.begin();
+    auto i = transitions_.end();
+    if (i != b)
+    {
+        for (--i; i != b; --i)
+        {
+            if (i->info->offset == i[-1].info->offset &&
+                i->info->abbrev == i[-1].info->abbrev &&
+                i->info->is_dst == i[-1].info->is_dst)
+                i = transitions_.erase(i);
+        }
+    }
+}
+
+void
+time_zone::init() const
+{
+    std::call_once(*adjusted_, [this]() {const_cast<time_zone*>(this)->init_impl();});
+}
+
+sys_info
+time_zone::load_sys_info(std::vector<detail::transition>::const_iterator i) const
+{
+    using namespace std::chrono;
+    assert(!transitions_.empty());
+    sys_info r;
+    if (i != transitions_.begin())
+    {
+        r.begin = i[-1].timepoint;
+        r.end = i != transitions_.end() ? i->timepoint :
+                                          sys_seconds(sys_days(year::max()/max_day));
+        r.offset = i[-1].info->offset;
+        r.save = i[-1].info->is_dst ? minutes{1} : minutes{0};
+        r.abbrev = i[-1].info->abbrev;
+    }
+    else
+    {
+        r.begin = sys_days(year::min()/min_day);
+        r.end = i+1 != transitions_.end() ? i[1].timepoint :
+                                          sys_seconds(sys_days(year::max()/max_day));
+        r.offset = i[0].info->offset;
+        r.save = i[0].info->is_dst ? minutes{1} : minutes{0};
+        r.abbrev = i[0].info->abbrev;
+    }
+    return r;
+}
+
+sys_info
+time_zone::get_info_impl(sys_seconds tp) const
+{
+    using namespace std;
+    init();
+    return load_sys_info(upper_bound(transitions_.begin(), transitions_.end(), tp,
+                                     [](const sys_seconds& x, const transition& t)
+                                     {
+                                         return x < t.timepoint;
+                                     }));
+}
+
+local_info
+time_zone::get_info_impl(local_seconds tp) const
+{
+    using namespace std::chrono;
+    init();
+    local_info i;
+    i.result = local_info::unique;
+    auto tr = upper_bound(transitions_.begin(), transitions_.end(), tp,
+                          [](const local_seconds& x, const transition& t)
+                          {
+                              return sys_seconds{x.time_since_epoch()} -
+                                                         t.info->offset < t.timepoint;
+                          });
+    i.first = load_sys_info(tr);
+    auto tps = sys_seconds{(tp - i.first.offset).time_since_epoch()};
+    if (tps < i.first.begin + days{1} && tr != transitions_.begin())
+    {
+        i.second = load_sys_info(--tr);
+        tps = sys_seconds{(tp - i.second.offset).time_since_epoch()};
+        if (tps < i.second.end && i.first.end != i.second.end)
+        {
+           i.result = local_info::ambiguous;
+           std::swap(i.first, i.second);
+        }
+        else
+        {
+            i.second = {};
+        }
+    }
+    else if (tps >= i.first.end && tr != transitions_.end())
+    {
+        i.second = load_sys_info(++tr);
+        tps = sys_seconds{(tp - i.second.offset).time_since_epoch()};
+        if (tps < i.second.begin)
+            i.result = local_info::nonexistent;
+        else
+            i.second = {};
+    }
+    return i;
+}
+
+std::ostream&
+operator<<(std::ostream& os, const time_zone& z)
+{
+    using namespace std::chrono;
+    z.init();
+    os << z.name_ << '\n';
+    os << "Initially:           ";
+    auto const& t = z.transitions_.front();
+    if (t.info->offset >= seconds{0})
+        os << '+';
+    os << make_time(t.info->offset);
+    if (t.info->is_dst > 0)
+        os << " daylight ";
+    else
+        os << " standard ";
+    os << t.info->abbrev << '\n';
+    for (auto i = std::next(z.transitions_.cbegin()); i < z.transitions_.cend(); ++i)
+        os << *i << '\n';
+    return os;
+}
+
+leap_second::leap_second(const sys_seconds& s, detail::undocumented)
+    : date_(s)
+{
+}
+
+#else  // !USE_OS_TZDB
+
+time_zone::time_zone(const std::string& s, detail::undocumented)
+    : adjusted_(new std::once_flag{})
+{
+    try
+    {
+        using namespace date;
+        std::istringstream in(s);
+        in.exceptions(std::ios::failbit | std::ios::badbit);
+        std::string word;
+        in >> word >> name_;
+        parse_info(in);
+    }
+    catch (...)
+    {
+        std::cerr << s << '\n';
+        std::cerr << *this << '\n';
+        zonelets_.pop_back();
+        throw;
+    }
+}
+
+sys_info
+time_zone::get_info_impl(sys_seconds tp) const
+{
+    return get_info_impl(tp, static_cast<int>(tz::utc));
+}
+
+local_info
+time_zone::get_info_impl(local_seconds tp) const
+{
+    using namespace std::chrono;
+    local_info i{};
+    i.first = get_info_impl(sys_seconds{tp.time_since_epoch()}, static_cast<int>(tz::local));
+    auto tps = sys_seconds{(tp - i.first.offset).time_since_epoch()};
+    if (tps < i.first.begin)
+    {
+        i.second = std::move(i.first);
+        i.first = get_info_impl(i.second.begin - seconds{1}, static_cast<int>(tz::utc));
+        i.result = local_info::nonexistent;
+    }
+    else if (i.first.end - tps <= days{1})
+    {
+        i.second = get_info_impl(i.first.end, static_cast<int>(tz::utc));
+        tps = sys_seconds{(tp - i.second.offset).time_since_epoch()};
+        if (tps >= i.second.begin)
+            i.result = local_info::ambiguous;
+        else
+            i.second = {};
+    }
+    return i;
+}
+
+void
+time_zone::add(const std::string& s)
+{
+    try
+    {
+        std::istringstream in(s);
+        in.exceptions(std::ios::failbit | std::ios::badbit);
+        ws(in);
+        if (!in.eof() && in.peek() != '#')
+            parse_info(in);
+    }
+    catch (...)
+    {
+        std::cerr << s << '\n';
+        std::cerr << *this << '\n';
+        zonelets_.pop_back();
+        throw;
+    }
+}
+
+void
+time_zone::parse_info(std::istream& in)
+{
+    using namespace date;
+    using namespace std::chrono;
+    zonelets_.emplace_back();
+    auto& zonelet = zonelets_.back();
+    zonelet.gmtoff_ = parse_signed_time(in);
+    in >> zonelet.u.rule_;
+    if (zonelet.u.rule_ == "-")
+        zonelet.u.rule_.clear();
+    in >> zonelet.format_;
+    if (!in.eof())
+        ws(in);
+    if (in.eof() || in.peek() == '#')
+    {
+        zonelet.until_year_ = year::max();
+        zonelet.until_date_ = MonthDayTime(max_day, tz::utc);
+    }
+    else
+    {
+        int y;
+        in >> y;
+        zonelet.until_year_ = year{y};
+        in >> zonelet.until_date_;
+        zonelet.until_date_.canonicalize(zonelet.until_year_);
+    }
+    if ((zonelet.until_year_ < min_year) ||
+            (zonelets_.size() > 1 && zonelets_.end()[-2].until_year_ > max_year))
+        zonelets_.pop_back();
+}
+
+void
+time_zone::adjust_infos(const std::vector<Rule>& rules)
+{
+    using namespace std::chrono;
+    using namespace date;
+    const zonelet* prev_zonelet = nullptr;
+    for (auto& z : zonelets_)
+    {
+        std::pair<const Rule*, const Rule*> eqr{};
+        std::istringstream in;
+        in.exceptions(std::ios::failbit | std::ios::badbit);
+        // Classify info as rule-based, has save, or neither
+        if (!z.u.rule_.empty())
+        {
+            // Find out if this zonelet has a rule or a save
+            eqr = std::equal_range(rules.data(), rules.data() + rules.size(), z.u.rule_);
+            if (eqr.first == eqr.second)
+            {
+                // The rule doesn't exist.  Assume this is a save
+                try
+                {
+                    using namespace std::chrono;
+                    using string = std::string;
+                    in.str(z.u.rule_);
+                    auto tmp = duration_cast<minutes>(parse_signed_time(in));
+#if !defined(_MSC_VER) || (_MSC_VER >= 1900)
+                    z.u.rule_.~string();
+                    z.tag_ = zonelet::has_save;
+                    ::new(&z.u.save_) minutes(tmp);
+#else
+                    z.u.rule_.clear();
+                    z.tag_ = zonelet::has_save;
+                    z.u.save_ = tmp;
+#endif
+                }
+                catch (...)
+                {
+                    std::cerr << name_ << " : " << z.u.rule_ << '\n';
+                    throw;
+                }
+            }
+        }
+        else
+        {
+            // This zone::zonelet has no rule and no save
+            z.tag_ = zonelet::is_empty;
+        }
+
+        minutes final_save{0};
+        if (z.tag_ == zonelet::has_save)
+        {
+            final_save = z.u.save_;
+        }
+        else if (z.tag_ == zonelet::has_rule)
+        {
+            z.last_rule_ = find_rule_for_zone(eqr, z.until_year_, z.gmtoff_,
+                                              z.until_date_);
+            if (z.last_rule_.first != nullptr)
+                final_save = z.last_rule_.first->save();
+        }
+        z.until_utc_ = z.until_date_.to_sys(z.until_year_, z.gmtoff_, final_save);
+        z.until_std_ = local_seconds{z.until_utc_.time_since_epoch()} + z.gmtoff_;
+        z.until_loc_ = z.until_std_ + final_save;
+
+        if (z.tag_ == zonelet::has_rule)
+        {
+            if (prev_zonelet != nullptr)
+            {
+                z.first_rule_ = find_rule_for_zone(eqr, prev_zonelet->until_utc_,
+                                                        prev_zonelet->until_std_,
+                                                        prev_zonelet->until_loc_);
+                if (z.first_rule_.first != nullptr)
+                {
+                    z.initial_save_ = z.first_rule_.first->save();
+                    z.initial_abbrev_ = z.first_rule_.first->abbrev();
+                    if (z.first_rule_ != z.last_rule_)
+                    {
+                        z.first_rule_ = find_next_rule(eqr.first, eqr.second,
+                                                       z.first_rule_.first,
+                                                       z.first_rule_.second);
+                    }
+                    else
+                    {
+                        z.first_rule_ = std::make_pair(nullptr, year::min());
+                        z.last_rule_ = std::make_pair(nullptr, year::max());
+                    }
+                }
+            }
+            if (z.first_rule_.first == nullptr && z.last_rule_.first != nullptr)
+            {
+                z.first_rule_ = std::make_pair(eqr.first, eqr.first->starting_year());
+                z.initial_abbrev_ = find_first_std_rule(eqr)->abbrev();
+            }
+        }
+
+#ifndef NDEBUG
+        if (z.first_rule_.first == nullptr)
+        {
+            assert(z.first_rule_.second == year::min());
+            assert(z.last_rule_.first == nullptr);
+            assert(z.last_rule_.second == year::max());
+        }
+        else
+        {
+            assert(z.last_rule_.first != nullptr);
+        }
+#endif
+        prev_zonelet = &z;
+    }
+}
+
+static
+std::string
+format_abbrev(std::string format, const std::string& variable, std::chrono::seconds off,
+                                                               std::chrono::minutes save)
+{
+    using namespace std::chrono;
+    auto k = format.find("%s");
+    if (k != std::string::npos)
+    {
+        format.replace(k, 2, variable);
+    }
+    else
+    {
+        k = format.find('/');
+        if (k != std::string::npos)
+        {
+            if (save == minutes{0})
+                format.erase(k);
+            else
+                format.erase(0, k+1);
+        }
+        else
+        {
+            k = format.find("%z");
+            if (k != std::string::npos)
+            {
+                std::string temp;
+                if (off < seconds{0})
+                {
+                    temp = '-';
+                    off = -off;
+                }
+                else
+                    temp = '+';
+                auto h = date::floor<hours>(off);
+                off -= h;
+                if (h < hours{10})
+                    temp += '0';
+                temp += std::to_string(h.count());
+                if (off > seconds{0})
+                {
+                    auto m = date::floor<minutes>(off);
+                    off -= m;
+                    if (m < minutes{10})
+                        temp += '0';
+                    temp += std::to_string(m.count());
+                    if (off > seconds{0})
+                    {
+                        if (off < seconds{10})
+                            temp += '0';
+                        temp += std::to_string(off.count());
+                    }
+                }
+                format.replace(k, 2, temp);
+            }
+        }
+    }
+    return format;
+}
+
+sys_info
+time_zone::get_info_impl(sys_seconds tp, int tz_int) const
+{
+    using namespace std::chrono;
+    using namespace date;
+    tz timezone = static_cast<tz>(tz_int);
+    assert(timezone != tz::standard);
+    auto y = year_month_day(floor<days>(tp)).year();
+    if (y < min_year || y > max_year)
+        throw std::runtime_error("The year " + std::to_string(static_cast<int>(y)) +
+            " is out of range:[" + std::to_string(static_cast<int>(min_year)) + ", "
+                                 + std::to_string(static_cast<int>(max_year)) + "]");
+    std::call_once(*adjusted_,
+                   [this]()
+                   {
+                       const_cast<time_zone*>(this)->adjust_infos(get_tzdb().rules);
+                   });
+    auto i = std::upper_bound(zonelets_.begin(), zonelets_.end(), tp,
+        [timezone](sys_seconds t, const zonelet& zl)
+        {
+            return timezone == tz::utc ? t < zl.until_utc_ :
+                                         t < sys_seconds{zl.until_loc_.time_since_epoch()};
+        });
+
+    sys_info r{};
+    if (i != zonelets_.end())
+    {
+        if (i->tag_ == zonelet::has_save)
+        {
+            if (i != zonelets_.begin())
+                r.begin = i[-1].until_utc_;
+            else
+                r.begin = sys_days(year::min()/min_day);
+            r.end = i->until_utc_;
+            r.offset = i->gmtoff_ + i->u.save_;
+            r.save = i->u.save_;
+        }
+        else if (i->u.rule_.empty())
+        {
+            if (i != zonelets_.begin())
+                r.begin = i[-1].until_utc_;
+            else
+                r.begin = sys_days(year::min()/min_day);
+            r.end = i->until_utc_;
+            r.offset = i->gmtoff_;
+        }
+        else
+        {
+            r = find_rule(i->first_rule_, i->last_rule_, y, i->gmtoff_,
+                          MonthDayTime(local_seconds{tp.time_since_epoch()}, timezone),
+                          i->initial_save_, i->initial_abbrev_);
+            r.offset = i->gmtoff_ + r.save;
+            if (i != zonelets_.begin() && r.begin < i[-1].until_utc_)
+                r.begin = i[-1].until_utc_;
+            if (r.end > i->until_utc_)
+                r.end = i->until_utc_;
+        }
+        r.abbrev = format_abbrev(i->format_, r.abbrev, r.offset, r.save);
+        assert(r.begin < r.end);
+    }
+    return r;
+}
+
+std::ostream&
+operator<<(std::ostream& os, const time_zone& z)
+{
+    using namespace date;
+    using namespace std::chrono;
+    detail::save_ostream<char> _(os);
+    os.fill(' ');
+    os.flags(std::ios::dec | std::ios::left);
+    std::call_once(*z.adjusted_,
+                   [&z]()
+                   {
+                       const_cast<time_zone&>(z).adjust_infos(get_tzdb().rules);
+                   });
+    os.width(35);
+    os << z.name_;
+    std::string indent;
+    for (auto const& s : z.zonelets_)
+    {
+        os << indent;
+        if (s.gmtoff_ >= seconds{0})
+            os << ' ';
+        os << make_time(s.gmtoff_) << "   ";
+        os.width(15);
+        if (s.tag_ != zonelet::has_save)
+            os << s.u.rule_;
+        else
+        {
+            std::ostringstream tmp;
+            tmp << make_time(s.u.save_);
+            os <<  tmp.str();
+        }
+        os.width(8);
+        os << s.format_ << "   ";
+        os << s.until_year_ << ' ' << s.until_date_;
+        os << "   " << s.until_utc_ << " UTC";
+        os << "   " << s.until_std_ << " STD";
+        os << "   " << s.until_loc_;
+        os << "   " << make_time(s.initial_save_);
+        os << "   " << s.initial_abbrev_;
+        if (s.first_rule_.first != nullptr)
+            os << "   {" << *s.first_rule_.first << ", " << s.first_rule_.second << '}';
+        else
+            os << "   {" << "nullptr" << ", " << s.first_rule_.second << '}';
+        if (s.last_rule_.first != nullptr)
+            os << "   {" << *s.last_rule_.first << ", " << s.last_rule_.second << '}';
+        else
+            os << "   {" << "nullptr" << ", " << s.last_rule_.second << '}';
+        os << '\n';
+        if (indent.empty())
+            indent = std::string(35, ' ');
+    }
+    return os;
+}
+
+#endif  // !USE_OS_TZDB
+
+std::ostream&
+operator<<(std::ostream& os, const leap_second& x)
+{
+    using namespace date;
+    return os << x.date_ << "  +";
+}
+
+#if USE_OS_TZDB
+
+static
+std::string
+get_version()
+{
+    using namespace std;
+    auto path = get_tz_dir() + string("/+VERSION");
+    ifstream in{path};
+    string version;
+    if (in)
+    {
+        in >> version;
+        return version;
+    }
+    in.clear();
+    in.open(get_tz_dir() + std::string(1, folder_delimiter) + "version");
+    if (in)
+    {
+        in >> version;
+        return version;
+    }
+    return "unknown";
+}
+
+static
+std::vector<leap_second>
+find_read_and_leap_seconds()
+{
+    std::ifstream in(get_tz_dir() + std::string(1, folder_delimiter) + "leapseconds",
+                     std::ios_base::binary);
+    if (in)
+    {
+        std::vector<leap_second> leap_seconds;
+        std::string line;
+        while (in)
+        {
+            std::getline(in, line);
+            if (!line.empty() && line[0] != '#')
+            {
+                std::istringstream in(line);
+                in.exceptions(std::ios::failbit | std::ios::badbit);
+                std::string word;
+                in >> word;
+                if (word == "Leap")
+                {
+                    int y, m, d;
+                    in >> y;
+                    m = static_cast<int>(parse_month(in));
+                    in >> d;
+                    leap_seconds.push_back(leap_second(sys_days{year{y}/m/d} + days{1},
+                                                                 detail::undocumented{}));
+                }
+                else
+                {
+                    std::cerr << line << '\n';
+                }
+            }
+        }
+        return leap_seconds;
+    }
+    in.clear();
+    in.open(get_tz_dir() + std::string(1, folder_delimiter) + "leap-seconds.list",
+                     std::ios_base::binary);
+    if (in)
+    {
+        std::vector<leap_second> leap_seconds;
+        std::string line;
+        const auto offset = sys_days{1970_y/1/1}-sys_days{1900_y/1/1};
+        while (in)
+        {
+            std::getline(in, line);
+            if (!line.empty() && line[0] != '#')
+            {
+                std::istringstream in(line);
+                in.exceptions(std::ios::failbit | std::ios::badbit);
+                using seconds = std::chrono::seconds;
+                seconds::rep s;
+                in >> s;
+                if (s == 2272060800)
+                    continue;
+                leap_seconds.push_back(leap_second(sys_seconds{seconds{s}} - offset,
+                                                                 detail::undocumented{}));
+            }
+        }
+        return leap_seconds;
+    }
+    in.clear();
+    in.open(get_tz_dir() + std::string(1, folder_delimiter) + "right/UTC",
+                     std::ios_base::binary);
+    if (in)
+    {
+        return load_just_leaps(in);
+    }
+    in.clear();
+    in.open(get_tz_dir() + std::string(1, folder_delimiter) + "UTC",
+                     std::ios_base::binary);
+    if (in)
+    {
+        return load_just_leaps(in);
+    }
+    return {};
+}
+
+static
+std::unique_ptr<tzdb>
+init_tzdb()
+{
+    std::unique_ptr<tzdb> db(new tzdb);
+
+    //Iterate through folders
+    std::queue<std::string> subfolders;
+    subfolders.emplace(get_tz_dir());
+    struct dirent* d;
+    struct stat s;
+    while (!subfolders.empty())
+    {
+        auto dirname = std::move(subfolders.front());
+        subfolders.pop();
+        auto dir = opendir(dirname.c_str());
+        if (!dir)
+            continue;
+        while ((d = readdir(dir)) != nullptr)
+        {
+            // Ignore these files:
+            if (d->d_name[0]                      == '.'    || // curdir, prevdir, hidden
+                memcmp(d->d_name, "posix", 5)     == 0      || // starts with posix
+                strcmp(d->d_name, "Factory")      == 0      ||
+                strcmp(d->d_name, "iso3166.tab")  == 0      ||
+                strcmp(d->d_name, "right")        == 0      ||
+                strcmp(d->d_name, "+VERSION")     == 0      ||
+                strcmp(d->d_name, "version")      == 0      ||
+                strcmp(d->d_name, "zone.tab")     == 0      ||
+                strcmp(d->d_name, "zone1970.tab") == 0      ||
+                strcmp(d->d_name, "tzdata.zi")    == 0      ||
+                strcmp(d->d_name, "leapseconds")  == 0      ||
+                strcmp(d->d_name, "leap-seconds.list") == 0   )
+                continue;
+            auto subname = dirname + folder_delimiter + d->d_name;
+            if(stat(subname.c_str(), &s) == 0)
+            {
+                if(S_ISDIR(s.st_mode))
+                {
+                    if(!S_ISLNK(s.st_mode))
+                    {
+                        subfolders.push(subname);
+                    }
+                }
+                else
+                {
+                    db->zones.emplace_back(subname.substr(get_tz_dir().size()+1),
+                                           detail::undocumented{});
+                }
+            }
+        }
+        closedir(dir);
+    }
+    db->zones.shrink_to_fit();
+    std::sort(db->zones.begin(), db->zones.end());
+    db->leap_seconds = find_read_and_leap_seconds();
+    db->version = get_version();
+    return db;
+}
+
+#else  // !USE_OS_TZDB
+
+// time_zone_link
+
+time_zone_link::time_zone_link(const std::string& s)
+{
+    using namespace date;
+    std::istringstream in(s);
+    in.exceptions(std::ios::failbit | std::ios::badbit);
+    std::string word;
+    in >> word >> target_ >> name_;
+}
+
+std::ostream&
+operator<<(std::ostream& os, const time_zone_link& x)
+{
+    using namespace date;
+    detail::save_ostream<char> _(os);
+    os.fill(' ');
+    os.flags(std::ios::dec | std::ios::left);
+    os.width(35);
+    return os << x.name_ << " --> " << x.target_;
+}
+
+// leap_second
+
+leap_second::leap_second(const std::string& s, detail::undocumented)
+{
+    using namespace date;
+    std::istringstream in(s);
+    in.exceptions(std::ios::failbit | std::ios::badbit);
+    std::string word;
+    int y;
+    MonthDayTime date;
+    in >> word >> y >> date;
+    date_ = date.to_time_point(year(y));
+}
+
+static
+bool
+file_exists(const std::string& filename)
+{
+#ifdef _WIN32
+    return ::_access(filename.c_str(), 0) == 0;
+#else
+    return ::access(filename.c_str(), F_OK) == 0;
+#endif
+}
+
+#if HAS_REMOTE_API
+
+// CURL tools
+
+namespace
+{
+
+struct curl_global_init_and_cleanup
+{
+    ~curl_global_init_and_cleanup()
+    {
+        ::curl_global_cleanup();
+    }
+    curl_global_init_and_cleanup()
+    {
+        if (::curl_global_init(CURL_GLOBAL_DEFAULT) != 0)
+            throw std::runtime_error("CURL global initialization failed");
+    }
+    curl_global_init_and_cleanup(curl_global_init_and_cleanup const&) = delete;
+    curl_global_init_and_cleanup& operator=(curl_global_init_and_cleanup const&) = delete;
+};
+
+struct curl_deleter
+{
+    void operator()(CURL* p) const
+    {
+        ::curl_easy_cleanup(p);
+    }
+};
+
+}  // unnamed namespace
+
+static
+std::unique_ptr<CURL, curl_deleter>
+curl_init()
+{
+    static const curl_global_init_and_cleanup _{};
+    return std::unique_ptr<CURL, curl_deleter>{::curl_easy_init()};
+}
+
+static
+bool
+download_to_string(const std::string& url, std::string& str)
+{
+    str.clear();
+    auto curl = curl_init();
+    if (!curl)
+        return false;
+    std::string version;
+    curl_easy_setopt(curl.get(), CURLOPT_USERAGENT, "curl");
+    curl_easy_setopt(curl.get(), CURLOPT_URL, url.c_str());
+    curl_write_callback write_cb = [](char* contents, std::size_t size, std::size_t nmemb,
+                                      void* userp) -> std::size_t
+    {
+        auto& userstr = *static_cast<std::string*>(userp);
+        auto realsize = size * nmemb;
+        userstr.append(contents, realsize);
+        return realsize;
+    };
+    curl_easy_setopt(curl.get(), CURLOPT_WRITEFUNCTION, write_cb);
+    curl_easy_setopt(curl.get(), CURLOPT_WRITEDATA, &str);
+    curl_easy_setopt(curl.get(), CURLOPT_SSL_VERIFYPEER, false);
+    auto res = curl_easy_perform(curl.get());
+    return (res == CURLE_OK);
+}
+
+namespace
+{
+    enum class download_file_options { binary, text };
+}
+
+static
+bool
+download_to_file(const std::string& url, const std::string& local_filename,
+                 download_file_options opts, char* error_buffer)
+{
+    auto curl = curl_init();
+    if (!curl)
+        return false;
+    curl_easy_setopt(curl.get(), CURLOPT_URL, url.c_str());
+    curl_easy_setopt(curl.get(), CURLOPT_SSL_VERIFYPEER, false);
+    if (error_buffer)
+       curl_easy_setopt(curl.get(), CURLOPT_ERRORBUFFER, error_buffer);
+    curl_write_callback write_cb = [](char* contents, std::size_t size, std::size_t nmemb,
+                                      void* userp) -> std::size_t
+    {
+        auto& of = *static_cast<std::ofstream*>(userp);
+        auto realsize = size * nmemb;
+        of.write(contents, static_cast<std::streamsize>(realsize));
+        return realsize;
+    };
+    curl_easy_setopt(curl.get(), CURLOPT_WRITEFUNCTION, write_cb);
+    decltype(curl_easy_perform(curl.get())) res;
+    {
+        std::ofstream of(local_filename,
+                         opts == download_file_options::binary ?
+                             std::ofstream::out | std::ofstream::binary :
+                             std::ofstream::out);
+        of.exceptions(std::ios::badbit);
+        curl_easy_setopt(curl.get(), CURLOPT_WRITEDATA, &of);
+        res = curl_easy_perform(curl.get());
+    }
+    return res == CURLE_OK;
+}
+
+std::string
+remote_version()
+{
+    std::string version;
+    std::string str;
+    if (download_to_string("https://www.iana.org/time-zones", str))
+    {
+        CONSTDATA char db[] = "/time-zones/releases/tzdata";
+        CONSTDATA auto db_size = sizeof(db) - 1;
+        auto p = str.find(db, 0, db_size);
+        const int ver_str_len = 5;
+        if (p != std::string::npos && p + (db_size + ver_str_len) <= str.size())
+            version = str.substr(p + db_size, ver_str_len);
+    }
+    return version;
+}
+
+
+// TODO! Using system() create a process and a console window.
+// This is useful to see what errors may occur but is slow and distracting.
+// Consider implementing this functionality more directly, such as
+// using _mkdir and CreateProcess etc.
+// But use the current means now as matches Unix implementations and while
+// in proof of concept / testing phase.
+// TODO! Use <filesystem> eventually.
+static
+bool
+remove_folder_and_subfolders(const std::string& folder)
+{
+#  ifdef _WIN32
+#    if USE_SHELL_API
+    // Delete the folder contents by deleting the folder.
+    std::string cmd = "rd /s /q \"";
+    cmd += folder;
+    cmd += '\"';
+    return std::system(cmd.c_str()) == EXIT_SUCCESS;
+#    else  // !USE_SHELL_API
+    // Create a buffer containing the path to delete. It must be terminated
+    // by two nuls. Who designs these API's...
+    std::vector<char> from;
+    from.assign(folder.begin(), folder.end());
+    from.push_back('\0');
+    from.push_back('\0');
+    SHFILEOPSTRUCT fo{}; // Zero initialize.
+    fo.wFunc = FO_DELETE;
+    fo.pFrom = from.data();
+    fo.fFlags = FOF_NO_UI;
+    int ret = SHFileOperation(&fo);
+    if (ret == 0 && !fo.fAnyOperationsAborted)
+        return true;
+    return false;
+#    endif  // !USE_SHELL_API
+#  else   // !_WIN32
+#    if USE_SHELL_API
+    return std::system(("rm -R " + folder).c_str()) == EXIT_SUCCESS;
+#    else // !USE_SHELL_API
+    struct dir_deleter {
+        dir_deleter() {}
+        void operator()(DIR* d) const
+        {
+            if (d != nullptr)
+            {
+                int result = closedir(d);
+                assert(result == 0);
+            }
+        }
+    };
+    using closedir_ptr = std::unique_ptr<DIR, dir_deleter>;
+
+    std::string filename;
+    struct stat statbuf;
+    std::size_t folder_len = folder.length();
+    struct dirent* p = nullptr;
+
+    closedir_ptr d(opendir(folder.c_str()));
+    bool r = d.get() != nullptr;
+    while (r && (p=readdir(d.get())) != nullptr)
+    {
+        if (strcmp(p->d_name, ".") == 0 || strcmp(p->d_name, "..") == 0)
+           continue;
+
+        // + 2 for path delimiter and nul terminator.
+        std::size_t buf_len = folder_len + strlen(p->d_name) + 2;
+        filename.resize(buf_len);
+        std::size_t path_len = static_cast<std::size_t>(
+            snprintf(&filename[0], buf_len, "%s/%s", folder.c_str(), p->d_name));
+        assert(path_len == buf_len - 1);
+        filename.resize(path_len);
+
+        if (stat(filename.c_str(), &statbuf) == 0)
+            r = S_ISDIR(statbuf.st_mode)
+              ? remove_folder_and_subfolders(filename)
+              : unlink(filename.c_str()) == 0;
+    }
+    d.reset();
+
+    if (r)
+        r = rmdir(folder.c_str()) == 0;
+
+    return r;
+#    endif // !USE_SHELL_API
+#  endif  // !_WIN32
+}
+
+static
+bool
+make_directory(const std::string& folder)
+{
+#  ifdef _WIN32
+#    if USE_SHELL_API
+    // Re-create the folder.
+    std::string cmd = "mkdir \"";
+    cmd += folder;
+    cmd += '\"';
+    return std::system(cmd.c_str()) == EXIT_SUCCESS;
+#    else  // !USE_SHELL_API
+    return _mkdir(folder.c_str()) == 0;
+#    endif // !USE_SHELL_API
+#  else  // !_WIN32
+#    if USE_SHELL_API
+    return std::system(("mkdir -p " + folder).c_str()) == EXIT_SUCCESS;
+#    else  // !USE_SHELL_API
+    return mkdir(folder.c_str(), 0777) == 0;
+#    endif  // !USE_SHELL_API
+#  endif  // !_WIN32
+}
+
+static
+bool
+delete_file(const std::string& file)
+{
+#  ifdef _WIN32
+#    if USE_SHELL_API
+    std::string cmd = "del \"";
+    cmd += file;
+    cmd += '\"';
+    return std::system(cmd.c_str()) == 0;
+#    else  // !USE_SHELL_API
+    return _unlink(file.c_str()) == 0;
+#    endif // !USE_SHELL_API
+#  else  // !_WIN32
+#    if USE_SHELL_API
+    return std::system(("rm " + file).c_str()) == EXIT_SUCCESS;
+#    else // !USE_SHELL_API
+    return unlink(file.c_str()) == 0;
+#    endif // !USE_SHELL_API
+#  endif  // !_WIN32
+}
+
+#  ifdef _WIN32
+
+static
+bool
+move_file(const std::string& from, const std::string& to)
+{
+#    if USE_SHELL_API
+    std::string cmd = "move \"";
+    cmd += from;
+    cmd += "\" \"";
+    cmd += to;
+    cmd += '\"';
+    return std::system(cmd.c_str()) == EXIT_SUCCESS;
+#    else  // !USE_SHELL_API
+    return !!::MoveFile(from.c_str(), to.c_str());
+#    endif // !USE_SHELL_API
+}
+
+// Usually something like "c:\Program Files".
+static
+std::string
+get_program_folder()
+{
+    return get_known_folder(FOLDERID_ProgramFiles);
+}
+
+// Note folder can and usually does contain spaces.
+static
+std::string
+get_unzip_program()
+{
+    std::string path;
+
+    // 7-Zip appears to note its location in the registry.
+    // If that doesn't work, fall through and take a guess, but it will likely be wrong.
+    HKEY hKey = nullptr;
+    if (RegOpenKeyExA(HKEY_LOCAL_MACHINE, "SOFTWARE\\7-Zip", 0, KEY_READ, &hKey) == ERROR_SUCCESS)
+    {
+        char value_buffer[MAX_PATH + 1]; // fyi 260 at time of writing.
+        // in/out parameter. Documentation say that size is a count of bytes not chars.
+        DWORD size = sizeof(value_buffer) - sizeof(value_buffer[0]);
+        DWORD tzi_type = REG_SZ;
+        // Testing shows Path key value is "C:\Program Files\7-Zip\" i.e. always with trailing \.
+        bool got_value = (RegQueryValueExA(hKey, "Path", nullptr, &tzi_type,
+            reinterpret_cast<LPBYTE>(value_buffer), &size) == ERROR_SUCCESS);
+        RegCloseKey(hKey); // Close now incase of throw later.
+        if (got_value)
+        {
+            // Function does not guarantee to null terminate.
+            value_buffer[size / sizeof(value_buffer[0])] = '\0';
+            path = value_buffer;
+            if (!path.empty())
+            {
+                path += "7z.exe";
+                return path;
+            }
+        }
+    }
+    path += get_program_folder();
+    path += folder_delimiter;
+    path += "7-Zip\\7z.exe";
+    return path;
+}
+
+#    if !USE_SHELL_API
+static
+int
+run_program(const std::string& command)
+{
+    STARTUPINFO si{};
+    si.cb = sizeof(si);
+    PROCESS_INFORMATION pi{};
+
+    // Allegedly CreateProcess overwrites the command line. Ugh.
+    std::string mutable_command(command);
+    if (CreateProcess(nullptr, &mutable_command[0],
+        nullptr, nullptr, FALSE, CREATE_NO_WINDOW, nullptr, nullptr, &si, &pi))
+    {
+        WaitForSingleObject(pi.hProcess, INFINITE);
+        DWORD exit_code;
+        bool got_exit_code = !!GetExitCodeProcess(pi.hProcess, &exit_code);
+        CloseHandle(pi.hProcess);
+        CloseHandle(pi.hThread);
+        // Not 100% sure about this still active thing is correct,
+        // but I'm going with it because I *think* WaitForSingleObject might
+        // return in some cases without INFINITE-ly waiting.
+        // But why/wouldn't GetExitCodeProcess return false in that case?
+        if (got_exit_code && exit_code != STILL_ACTIVE)
+            return static_cast<int>(exit_code);
+    }
+    return EXIT_FAILURE;
+}
+#    endif // !USE_SHELL_API
+
+static
+std::string
+get_download_tar_file(const std::string& version)
+{
+    auto file = get_install();
+    file += folder_delimiter;
+    file += "tzdata";
+    file += version;
+    file += ".tar";
+    return file;
+}
+
+static
+bool
+extract_gz_file(const std::string& version, const std::string& gz_file,
+                const std::string& dest_folder)
+{
+    auto unzip_prog = get_unzip_program();
+    bool unzip_result = false;
+    // Use the unzip program to extract the tar file from the archive.
+
+    // Aim to create a string like:
+    // "C:\Program Files\7-Zip\7z.exe" x "C:\Users\SomeUser\Downloads\tzdata2016d.tar.gz"
+    //     -o"C:\Users\SomeUser\Downloads\tzdata"
+    std::string cmd;
+    cmd = '\"';
+    cmd += unzip_prog;
+    cmd += "\" x \"";
+    cmd += gz_file;
+    cmd += "\" -o\"";
+    cmd += dest_folder;
+    cmd += '\"';
+
+#    if USE_SHELL_API
+    // When using shelling out with std::system() extra quotes are required around the
+    // whole command. It's weird but necessary it seems, see:
+    // http://stackoverflow.com/q/27975969/576911
+
+    cmd = "\"" + cmd + "\"";
+    if (std::system(cmd.c_str()) == EXIT_SUCCESS)
+        unzip_result = true;
+#    else  // !USE_SHELL_API
+    if (run_program(cmd) == EXIT_SUCCESS)
+        unzip_result = true;
+#    endif // !USE_SHELL_API
+    if (unzip_result)
+        delete_file(gz_file);
+
+    // Use the unzip program extract the data from the tar file that was
+    // just extracted from the archive.
+    auto tar_file = get_download_tar_file(version);
+    cmd = '\"';
+    cmd += unzip_prog;
+    cmd += "\" x \"";
+    cmd += tar_file;
+    cmd += "\" -o\"";
+    cmd += get_install();
+    cmd += '\"';
+#    if USE_SHELL_API
+    cmd = "\"" + cmd + "\"";
+    if (std::system(cmd.c_str()) == EXIT_SUCCESS)
+        unzip_result = true;
+#    else  // !USE_SHELL_API
+    if (run_program(cmd) == EXIT_SUCCESS)
+        unzip_result = true;
+#    endif // !USE_SHELL_API
+
+    if (unzip_result)
+        delete_file(tar_file);
+
+    return unzip_result;
+}
+
+static
+std::string
+get_download_mapping_file(const std::string& version)
+{
+    auto file = get_install() + version + "windowsZones.xml";
+    return file;
+}
+
+#  else  // !_WIN32
+
+#    if !USE_SHELL_API
+static
+int
+run_program(const char* prog, const char*const args[])
+{
+    pid_t pid = fork();
+    if (pid == -1) // Child failed to start.
+        return EXIT_FAILURE;
+
+    if (pid != 0)
+    {
+        // We are in the parent. Child started. Wait for it.
+        pid_t ret;
+        int status;
+        while ((ret = waitpid(pid, &status, 0)) == -1)
+        {
+            if (errno != EINTR)
+                break;
+        }
+        if (ret != -1)
+        {
+            if (WIFEXITED(status))
+                return WEXITSTATUS(status);
+        }
+        printf("Child issues!\n");
+
+        return EXIT_FAILURE; // Not sure what status of child is.
+    }
+    else // We are in the child process. Start the program the parent wants to run.
+    {
+
+        if (execv(prog, const_cast<char**>(args)) == -1) // Does not return.
+        {
+            perror("unreachable 0\n");
+            _Exit(127);
+        }
+        printf("unreachable 2\n");
+    }
+    printf("unreachable 2\n");
+    // Unreachable.
+    assert(false);
+    exit(EXIT_FAILURE);
+    return EXIT_FAILURE;
+}
+#    endif // !USE_SHELL_API
+
+static
+bool
+extract_gz_file(const std::string&, const std::string& gz_file, const std::string&)
+{
+#    if USE_SHELL_API
+    bool unzipped = std::system(("tar -xzf " + gz_file + " -C " + get_install()).c_str()) == EXIT_SUCCESS;
+#    else  // !USE_SHELL_API
+    const char prog[] = {"/usr/bin/tar"};
+    const char*const args[] =
+    {
+        prog, "-xzf", gz_file.c_str(), "-C", get_install().c_str(), nullptr
+    };
+    bool unzipped = (run_program(prog, args) == EXIT_SUCCESS);
+#    endif // !USE_SHELL_API
+    if (unzipped)
+    {
+        delete_file(gz_file);
+        return true;
+    }
+    return false;
+}
+
+#  endif // !_WIN32
+
+bool
+remote_download(const std::string& version, char* error_buffer)
+{
+    assert(!version.empty());
+
+#  ifdef _WIN32
+    // Download folder should be always available for Windows
+#  else  // !_WIN32
+    // Create download folder if it does not exist on UNIX system
+    auto download_folder = get_install();
+    if (!file_exists(download_folder))
+    {
+        if (!make_directory(download_folder))
+            return false;
+    }
+#  endif  // _WIN32
+
+    auto url = "https://data.iana.org/time-zones/releases/tzdata" + version +
+               ".tar.gz";
+    bool result = download_to_file(url, get_download_gz_file(version),
+                                   download_file_options::binary, error_buffer);
+#  ifdef _WIN32
+    if (result)
+    {
+        auto mapping_file = get_download_mapping_file(version);
+        result = download_to_file(
+            "https://raw.githubusercontent.com/unicode-org/cldr/master/"
+            "common/supplemental/windowsZones.xml",
+            mapping_file, download_file_options::text, error_buffer);
+    }
+#  endif  // _WIN32
+    return result;
+}
+
+bool
+remote_install(const std::string& version)
+{
+    auto success = false;
+    assert(!version.empty());
+
+    std::string install = get_install();
+    auto gz_file = get_download_gz_file(version);
+    if (file_exists(gz_file))
+    {
+        if (file_exists(install))
+            remove_folder_and_subfolders(install);
+        if (make_directory(install))
+        {
+            if (extract_gz_file(version, gz_file, install))
+                success = true;
+#  ifdef _WIN32
+            auto mapping_file_source = get_download_mapping_file(version);
+            auto mapping_file_dest = get_install();
+            mapping_file_dest += folder_delimiter;
+            mapping_file_dest += "windowsZones.xml";
+            if (!move_file(mapping_file_source, mapping_file_dest))
+                success = false;
+#  endif  // _WIN32
+        }
+    }
+    return success;
+}
+
+#endif  // HAS_REMOTE_API
+
+static
+std::string
+get_version(const std::string& path)
+{
+    std::string version;
+    std::ifstream infile(path + "version");
+    if (infile.is_open())
+    {
+        infile >> version;
+        if (!infile.fail())
+            return version;
+    }
+    else
+    {
+        infile.open(path + "NEWS");
+        while (infile)
+        {
+            infile >> version;
+            if (version == "Release")
+            {
+                infile >> version;
+                return version;
+            }
+        }
+    }
+    throw std::runtime_error("Unable to get Timezone database version from " + path);
+}
+
+static
+std::unique_ptr<tzdb>
+init_tzdb()
+{
+    using namespace date;
+    const std::string install = get_install();
+    const std::string path = install + folder_delimiter;
+    std::string line;
+    bool continue_zone = false;
+    std::unique_ptr<tzdb> db(new tzdb);
+
+#if AUTO_DOWNLOAD
+    if (!file_exists(install))
+    {
+        auto rv = remote_version();
+        if (!rv.empty() && remote_download(rv))
+        {
+            if (!remote_install(rv))
+            {
+                std::string msg = "Timezone database version \"";
+                msg += rv;
+                msg += "\" did not install correctly to \"";
+                msg += install;
+                msg += "\"";
+                throw std::runtime_error(msg);
+            }
+        }
+        if (!file_exists(install))
+        {
+            std::string msg = "Timezone database not found at \"";
+            msg += install;
+            msg += "\"";
+            throw std::runtime_error(msg);
+        }
+        db->version = get_version(path);
+    }
+    else
+    {
+        db->version = get_version(path);
+        auto rv = remote_version();
+        if (!rv.empty() && db->version != rv)
+        {
+            if (remote_download(rv))
+            {
+                remote_install(rv);
+                db->version = get_version(path);
+            }
+        }
+    }
+#else  // !AUTO_DOWNLOAD
+    if (!file_exists(install))
+    {
+        std::string msg = "Timezone database not found at \"";
+        msg += install;
+        msg += "\"";
+        throw std::runtime_error(msg);
+    }
+    db->version = get_version(path);
+#endif  // !AUTO_DOWNLOAD
+
+    CONSTDATA char*const files[] =
+    {
+        "africa", "antarctica", "asia", "australasia", "backward", "etcetera", "europe",
+        "pacificnew", "northamerica", "southamerica", "systemv", "leapseconds"
+    };
+
+    for (const auto& filename : files)
+    {
+        std::ifstream infile(path + filename);
+        while (infile)
+        {
+            std::getline(infile, line);
+            if (!line.empty() && line[0] != '#')
+            {
+                std::istringstream in(line);
+                std::string word;
+                in >> word;
+                if (word == "Rule")
+                {
+                    db->rules.push_back(Rule(line));
+                    continue_zone = false;
+                }
+                else if (word == "Link")
+                {
+                    db->links.push_back(time_zone_link(line));
+                    continue_zone = false;
+                }
+                else if (word == "Leap")
+                {
+                    db->leap_seconds.push_back(leap_second(line, detail::undocumented{}));
+                    continue_zone = false;
+                }
+                else if (word == "Zone")
+                {
+                    db->zones.push_back(time_zone(line, detail::undocumented{}));
+                    continue_zone = true;
+                }
+                else if (line[0] == '\t' && continue_zone)
+                {
+                    db->zones.back().add(line);
+                }
+                else
+                {
+                    std::cerr << line << '\n';
+                }
+            }
+        }
+    }
+    std::sort(db->rules.begin(), db->rules.end());
+    Rule::split_overlaps(db->rules);
+    std::sort(db->zones.begin(), db->zones.end());
+    db->zones.shrink_to_fit();
+    std::sort(db->links.begin(), db->links.end());
+    db->links.shrink_to_fit();
+    std::sort(db->leap_seconds.begin(), db->leap_seconds.end());
+    db->leap_seconds.shrink_to_fit();
+
+#ifdef _WIN32
+    std::string mapping_file = get_install() + folder_delimiter + "windowsZones.xml";
+    db->mappings = load_timezone_mappings_from_xml_file(mapping_file);
+    sort_zone_mappings(db->mappings);
+#endif // _WIN32
+
+    return db;
+}
+
+const tzdb&
+reload_tzdb()
+{
+#if AUTO_DOWNLOAD
+    auto const& v = get_tzdb_list().front().version;
+    if (!v.empty() && v == remote_version())
+        return get_tzdb_list().front();
+#endif  // AUTO_DOWNLOAD
+    tzdb_list::undocumented_helper::push_front(get_tzdb_list(), init_tzdb().release());
+    return get_tzdb_list().front();
+}
+
+#endif  // !USE_OS_TZDB
+
+const tzdb&
+get_tzdb()
+{
+    return get_tzdb_list().front();
+}
+
+const time_zone*
+#if HAS_STRING_VIEW
+tzdb::locate_zone(std::string_view tz_name) const
+#else
+tzdb::locate_zone(const std::string& tz_name) const
+#endif
+{
+    auto zi = std::lower_bound(zones.begin(), zones.end(), tz_name,
+#if HAS_STRING_VIEW
+        [](const time_zone& z, const std::string_view& nm)
+#else
+        [](const time_zone& z, const std::string& nm)
+#endif
+        {
+            return z.name() < nm;
+        });
+    if (zi == zones.end() || zi->name() != tz_name)
+    {
+#if !USE_OS_TZDB
+        auto li = std::lower_bound(links.begin(), links.end(), tz_name,
+#if HAS_STRING_VIEW
+        [](const time_zone_link& z, const std::string_view& nm)
+#else
+        [](const time_zone_link& z, const std::string& nm)
+#endif
+        {
+            return z.name() < nm;
+        });
+        if (li != links.end() && li->name() == tz_name)
+        {
+            zi = std::lower_bound(zones.begin(), zones.end(), li->target(),
+                [](const time_zone& z, const std::string& nm)
+                {
+                    return z.name() < nm;
+                });
+            if (zi != zones.end() && zi->name() == li->target())
+                return &*zi;
+        }
+#endif  // !USE_OS_TZDB
+        throw std::runtime_error(std::string(tz_name) + " not found in timezone database");
+    }
+    return &*zi;
+}
+
+const time_zone*
+#if HAS_STRING_VIEW
+locate_zone(std::string_view tz_name)
+#else
+locate_zone(const std::string& tz_name)
+#endif
+{
+    return get_tzdb().locate_zone(tz_name);
+}
+
+#if USE_OS_TZDB
+
+std::ostream&
+operator<<(std::ostream& os, const tzdb& db)
+{
+    os << "Version: " << db.version << "\n\n";
+    for (const auto& x : db.zones)
+        os << x << '\n';
+    os << '\n';
+    for (const auto& x : db.leap_seconds)
+        os << x << '\n';
+    return os;
+}
+
+#else  // !USE_OS_TZDB
+
+std::ostream&
+operator<<(std::ostream& os, const tzdb& db)
+{
+    os << "Version: " << db.version << '\n';
+    std::string title("--------------------------------------------"
+                      "--------------------------------------------\n"
+                      "Name           ""Start Y ""End Y   "
+                      "Beginning                              ""Offset  "
+                      "Designator\n"
+                      "--------------------------------------------"
+                      "--------------------------------------------\n");
+    int count = 0;
+    for (const auto& x : db.rules)
+    {
+        if (count++ % 50 == 0)
+            os << title;
+        os << x << '\n';
+    }
+    os << '\n';
+    title = std::string("---------------------------------------------------------"
+                        "--------------------------------------------------------\n"
+                        "Name                               ""Offset      "
+                        "Rule           ""Abrev      ""Until\n"
+                        "---------------------------------------------------------"
+                        "--------------------------------------------------------\n");
+    count = 0;
+    for (const auto& x : db.zones)
+    {
+        if (count++ % 10 == 0)
+            os << title;
+        os << x << '\n';
+    }
+    os << '\n';
+    title = std::string("---------------------------------------------------------"
+                        "--------------------------------------------------------\n"
+                        "Alias                                   ""To\n"
+                        "---------------------------------------------------------"
+                        "--------------------------------------------------------\n");
+    count = 0;
+    for (const auto& x : db.links)
+    {
+        if (count++ % 45 == 0)
+            os << title;
+        os << x << '\n';
+    }
+    os << '\n';
+    title = std::string("---------------------------------------------------------"
+                        "--------------------------------------------------------\n"
+                        "Leap second on\n"
+                        "---------------------------------------------------------"
+                        "--------------------------------------------------------\n");
+    os << title;
+    for (const auto& x : db.leap_seconds)
+        os << x << '\n';
+    return os;
+}
+
+#endif  // !USE_OS_TZDB
+
+// -----------------------
+
+#ifdef _WIN32
+
+static
+std::string
+getTimeZoneKeyName()
+{
+    DYNAMIC_TIME_ZONE_INFORMATION dtzi{};
+    auto result = GetDynamicTimeZoneInformation(&dtzi);
+    if (result == TIME_ZONE_ID_INVALID)
+        throw std::runtime_error("current_zone(): GetDynamicTimeZoneInformation()"
+                                 " reported TIME_ZONE_ID_INVALID.");
+    auto wlen = wcslen(dtzi.TimeZoneKeyName);
+    char buf[128] = {};
+    assert(sizeof(buf) >= wlen+1);
+    wcstombs(buf, dtzi.TimeZoneKeyName, wlen);
+    if (strcmp(buf, "Coordinated Universal Time") == 0)
+        return "UTC";
+    return buf;
+}
+
+const time_zone*
+tzdb::current_zone() const
+{
+    std::string win_tzid = getTimeZoneKeyName();
+    std::string standard_tzid;
+    if (!native_to_standard_timezone_name(win_tzid, standard_tzid))
+    {
+        std::string msg;
+        msg = "current_zone() failed: A mapping from the Windows Time Zone id \"";
+        msg += win_tzid;
+        msg += "\" was not found in the time zone mapping database.";
+        throw std::runtime_error(msg);
+    }
+    return locate_zone(standard_tzid);
+}
+
+#else  // !_WIN32
+
+#if HAS_STRING_VIEW
+
+static
+std::string_view
+extract_tz_name(char const* rp)
+{
+    using namespace std;
+    string_view result = rp;
+    CONSTDATA string_view zoneinfo = "zoneinfo";
+    size_t pos = result.rfind(zoneinfo);
+    if (pos == result.npos)
+        throw runtime_error(
+            "current_zone() failed to find \"zoneinfo\" in " + string(result));
+    pos = result.find('/', pos);
+    result.remove_prefix(pos + 1);
+    return result;
+}
+
+#else  // !HAS_STRING_VIEW
+
+static
+std::string
+extract_tz_name(char const* rp)
+{
+    using namespace std;
+    string result = rp;
+    CONSTDATA char zoneinfo[] = "zoneinfo";
+    size_t pos = result.rfind(zoneinfo);
+    if (pos == result.npos)
+        throw runtime_error(
+            "current_zone() failed to find \"zoneinfo\" in " + result);
+    pos = result.find('/', pos);
+    result.erase(0, pos + 1);
+    return result;
+}
+
+#endif  // HAS_STRING_VIEW
+
+static
+bool
+sniff_realpath(const char* timezone)
+{
+    using namespace std;
+    char rp[PATH_MAX+1] = {};
+    if (realpath(timezone, rp) == nullptr)
+        throw system_error(errno, system_category(), "realpath() failed");
+    auto result = extract_tz_name(rp);
+    return result != "posixrules";
+}
+
+const time_zone*
+tzdb::current_zone() const
+{
+    // On some OS's a file called /etc/localtime may
+    // exist and it may be either a real file
+    // containing time zone details or a symlink to such a file.
+    // On MacOS and BSD Unix if this file is a symlink it
+    // might resolve to a path like this:
+    // "/usr/share/zoneinfo/America/Los_Angeles"
+    // If it does, we try to determine the current
+    // timezone from the remainder of the path by removing the prefix
+    // and hoping the rest resolves to a valid timezone.
+    // It may not always work though. If it doesn't then an
+    // exception will be thrown by local_timezone.
+    // The path may also take a relative form:
+    // "../usr/share/zoneinfo/America/Los_Angeles".
+    {
+        struct stat sb;
+        CONSTDATA auto timezone = "/etc/localtime";
+        if (lstat(timezone, &sb) == 0 && S_ISLNK(sb.st_mode) && sb.st_size > 0)
+        {
+            using namespace std;
+            static const bool use_realpath = sniff_realpath(timezone);
+            char rp[PATH_MAX+1] = {};
+            if (use_realpath)
+            {
+                if (realpath(timezone, rp) == nullptr)
+                    throw system_error(errno, system_category(), "realpath() failed");
+            }
+            else
+            {
+                if (readlink(timezone, rp, sizeof(rp)-1) <= 0)
+                    throw system_error(errno, system_category(), "readlink() failed");
+            }
+            return locate_zone(extract_tz_name(rp));
+        }
+    }
+    // On embedded systems e.g. buildroot with uclibc the timezone is linked
+    // into /etc/TZ which is a symlink to path like this:
+    // "/usr/share/zoneinfo/uclibc/America/Los_Angeles"
+    // If it does, we try to determine the current
+    // timezone from the remainder of the path by removing the prefix
+    // and hoping the rest resolves to valid timezone.
+    // It may not always work though. If it doesn't then an
+    // exception will be thrown by local_timezone.
+    // The path may also take a relative form:
+    // "../usr/share/zoneinfo/uclibc/America/Los_Angeles".
+    {
+        struct stat sb;
+        CONSTDATA auto timezone = "/etc/TZ";
+        if (lstat(timezone, &sb) == 0 && S_ISLNK(sb.st_mode) && sb.st_size > 0) {
+            using namespace std;
+            string result;
+            char rp[PATH_MAX+1] = {};
+            if (readlink(timezone, rp, sizeof(rp)-1) > 0)
+                result = string(rp);
+            else
+                throw system_error(errno, system_category(), "readlink() failed");
+
+            const size_t pos = result.find(get_tz_dir());
+            if (pos != result.npos)
+                result.erase(0, get_tz_dir().size() + 1 + pos);
+            return locate_zone(result);
+        }
+    }
+    {
+    // On some versions of some linux distro's (e.g. Ubuntu),
+    // the current timezone might be in the first line of
+    // the /etc/timezone file.
+        std::ifstream timezone_file("/etc/timezone");
+        if (timezone_file.is_open())
+        {
+            std::string result;
+            std::getline(timezone_file, result);
+            if (!result.empty())
+                return locate_zone(result);
+        }
+        // Fall through to try other means.
+    }
+    {
+    // On some versions of some bsd distro's (e.g. FreeBSD),
+    // the current timezone might be in the first line of
+    // the /var/db/zoneinfo file.
+        std::ifstream timezone_file("/var/db/zoneinfo");
+        if (timezone_file.is_open())
+        {
+            std::string result;
+            std::getline(timezone_file, result);
+            if (!result.empty())
+                return locate_zone(result);
+        }
+        // Fall through to try other means.
+    }
+    {
+    // On some versions of some bsd distro's (e.g. iOS),
+    // it is not possible to use file based approach,
+    // we switch to system API, calling functions in
+    // CoreFoundation framework.
+#if TARGET_OS_IPHONE
+        std::string result = date::iOSUtils::get_current_timezone();
+        if (!result.empty())
+            return locate_zone(result);
+#endif
+    // Fall through to try other means.
+    }
+    {
+    // On some versions of some linux distro's (e.g. Red Hat),
+    // the current timezone might be in the first line of
+    // the /etc/sysconfig/clock file as:
+    // ZONE="US/Eastern"
+        std::ifstream timezone_file("/etc/sysconfig/clock");
+        std::string result;
+        while (timezone_file)
+        {
+            std::getline(timezone_file, result);
+            auto p = result.find("ZONE=\"");
+            if (p != std::string::npos)
+            {
+                result.erase(p, p+6);
+                result.erase(result.rfind('"'));
+                return locate_zone(result);
+            }
+        }
+        // Fall through to try other means.
+    }
+    throw std::runtime_error("Could not get current timezone");
+}
+
+#endif  // !_WIN32
+
+const time_zone*
+current_zone()
+{
+    return get_tzdb().current_zone();
+}
+
+}  // namespace date
+
+#if defined(__GNUC__) && __GNUC__ < 5
+# pragma GCC diagnostic pop
+#endif
diff --git a/third_party/date-3.0.1/test/clock_cast_test/constexpr.pass.cpp b/third_party/date-3.0.1/test/clock_cast_test/constexpr.pass.cpp
new file mode 100644
index 00000000..5fdb7583
--- /dev/null
+++ b/third_party/date-3.0.1/test/clock_cast_test/constexpr.pass.cpp
@@ -0,0 +1,75 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2019 nanoric
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+#include "tz.h"
+#include <cassert>
+#include <type_traits>
+
+struct const_clock {
+  using duration =
+      typename std::common_type<std::chrono::system_clock::duration,
+          date::days>::type;
+  using rep = duration::rep;
+  using period = duration::period;
+  using time_point = std::chrono::time_point<const_clock, duration>;
+
+  static constexpr date::sys_days epoch { date::days { 1000 } };
+
+  template <typename Duration>
+  static std::chrono::time_point<std::chrono::system_clock,
+      typename std::common_type<Duration, date::days>::type>
+      CONSTCD11 to_sys(std::chrono::time_point<const_clock, Duration> const& tp)
+  {
+    return epoch + tp.time_since_epoch();
+  }
+
+  template <typename Duration>
+  static std::chrono::time_point<const_clock,
+      typename std::common_type<Duration, date::days>::type>
+      CONSTCD11 from_sys(
+          std::chrono::time_point<std::chrono::system_clock, Duration> const&
+              tp)
+  {
+    using res = std::chrono::time_point<const_clock,
+        typename std::common_type<Duration, date::days>::type>;
+    return res(tp - epoch);
+  }
+};
+
+int main()
+{
+  using namespace date;
+  using namespace std::chrono;
+  using const_days = time_point<const_clock, days>;
+
+  CONSTCD14 sys_days sys { days { 1024 } };
+  static_assert(sys.time_since_epoch().count() == 1024, "");
+
+  CONSTCD14 const_days c {clock_cast<const_clock>(sys)};
+  CONSTCD14 sys_days sys2 {clock_cast<system_clock>(c)};
+  CONSTCD14 sys_days sys3 { clock_cast<system_clock>(const_days(days(48))) };
+#if __cplusplus >= 201402L
+  static_assert(c.time_since_epoch().count() == 24, "");
+  static_assert(sys2.time_since_epoch().count() == 1024, "");
+  static_assert(sys3.time_since_epoch().count() == 1048, "");
+#endif
+}
diff --git a/third_party/date-3.0.1/test/clock_cast_test/custom_clock.pass.cpp b/third_party/date-3.0.1/test/clock_cast_test/custom_clock.pass.cpp
new file mode 100644
index 00000000..1c64a5d8
--- /dev/null
+++ b/third_party/date-3.0.1/test/clock_cast_test/custom_clock.pass.cpp
@@ -0,0 +1,213 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2017, 2018 Tomasz Kamiński
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+#include "tz.h"
+#include <cassert>
+#include <type_traits>
+
+//used to count number of conversion
+int conversions = 0;
+
+//to/from impl
+struct mil_clock
+{
+  using duration = typename std::common_type<std::chrono::system_clock::duration, date::days>::type;
+  using rep = duration::rep;
+  using period = duration::period;
+  using time_point = std::chrono::time_point<mil_clock, duration>;
+
+  static constexpr date::sys_days epoch{date::days{1000}};
+
+  template<typename Duration>
+  static
+  std::chrono::time_point<std::chrono::system_clock, typename std::common_type<Duration, date::days>::type>
+  to_sys(std::chrono::time_point<mil_clock, Duration> const& tp)
+  {
+    ++conversions;
+    return epoch + tp.time_since_epoch();
+  }
+
+  template<typename Duration>
+  static
+  std::chrono::time_point<mil_clock, typename std::common_type<Duration, date::days>::type>
+  from_sys(std::chrono::time_point<std::chrono::system_clock, Duration> const& tp)
+  {
+    ++conversions;
+    using res = std::chrono::time_point<mil_clock, typename std::common_type<Duration, date::days>::type>;
+    return res(tp - epoch);
+  }
+
+  template<typename Duration>
+  static
+  std::chrono::time_point<date::local_t, typename std::common_type<Duration, date::days>::type>
+  to_local(std::chrono::time_point<mil_clock, Duration> const& tp)
+  {
+     return date::clock_cast<date::local_t>(to_sys(tp));
+  }
+
+  template<typename Duration>
+  static
+  std::chrono::time_point<mil_clock, typename std::common_type<Duration, date::days>::type>
+  from_local(std::chrono::time_point<date::local_t, Duration> const& tp)
+  {
+    return from_sys(date::clock_cast<std::chrono::system_clock>(tp));
+  }
+
+
+  static time_point now()
+  {
+    return from_sys(std::chrono::system_clock::now());
+  }
+};
+
+
+date::sys_days const mil_clock::epoch;
+
+// traits example
+struct s2s_clock
+{
+  using duration = std::chrono::system_clock::duration;
+  using rep = duration::rep;
+  using period = duration::period;
+  using time_point = std::chrono::time_point<s2s_clock, duration>;
+
+  template<typename Duration>
+  static
+  std::chrono::time_point<std::chrono::system_clock, Duration>
+  to_sys(std::chrono::time_point<s2s_clock, Duration> const& tp)
+  {
+    ++conversions;
+    return std::chrono::time_point<std::chrono::system_clock, Duration>(tp.time_since_epoch());
+  }
+
+  template<typename Duration>
+  static
+  std::chrono::time_point<s2s_clock, Duration>
+  from_sys(std::chrono::time_point<std::chrono::system_clock, Duration> const& tp)
+  {
+    ++conversions;
+    return std::chrono::time_point<s2s_clock, Duration>(tp.time_since_epoch());
+  }
+
+  static time_point now()
+  {
+    return from_sys(std::chrono::system_clock::now());
+  }
+};
+
+namespace date
+{
+   template<>
+   struct clock_time_conversion<mil_clock, s2s_clock>
+   {
+     template<typename Duration>
+     std::chrono::time_point<mil_clock, typename std::common_type<Duration, date::days>::type>
+     operator()(std::chrono::time_point<s2s_clock, Duration> const& tp)
+     {
+       ++conversions;
+       using res = std::chrono::time_point<mil_clock, typename std::common_type<Duration, date::days>::type>;
+       return res(tp.time_since_epoch() - mil_clock::epoch.time_since_epoch());
+     }
+   };
+}
+
+int
+main()
+{
+    using namespace date;
+    using sys_clock = std::chrono::system_clock;
+
+    // self
+    {
+       sys_days st(1997_y/dec/12);
+       auto mt = mil_clock::from_sys(st);
+
+       assert(clock_cast<mil_clock>(mt) == mt);
+    }
+
+    // mil <-> local
+    {
+       local_days lt(1997_y/dec/12);
+       auto mt = mil_clock::from_local(lt);
+
+       assert(clock_cast<mil_clock>(lt) == mt);
+       assert(clock_cast<local_t>(mt) == lt);
+    }
+
+    // mil <-> sys
+    {
+       sys_days st(1997_y/dec/12);
+       auto mt = mil_clock::from_sys(st);
+
+       assert(clock_cast<mil_clock>(st) == mt);
+       assert(clock_cast<sys_clock>(mt) == st);
+    }
+
+    // mil <-> utc
+    {
+       sys_days st(1997_y/dec/12);
+       auto mt = mil_clock::from_sys(st);
+       auto ut = utc_clock::from_sys(st);
+
+       assert(clock_cast<mil_clock>(ut) == mt);
+       assert(clock_cast<utc_clock>(mt) == ut);
+    }
+
+    // mil <-> tai
+    {
+       sys_days st(1997_y/dec/12);
+       auto mt = mil_clock::from_sys(st);
+       auto ut = utc_clock::from_sys(st);
+       auto tt = tai_clock::from_utc(ut);
+
+       assert(clock_cast<tai_clock>(mt) == tt);
+       assert(clock_cast<mil_clock>(tt) == mt);
+    }
+
+    // mil <-> gps
+    {
+       sys_days st(1997_y/dec/12);
+       auto mt = mil_clock::from_sys(st);
+       auto ut = utc_clock::from_sys(st);
+       auto gt = gps_clock::from_utc(ut);
+
+       assert(clock_cast<gps_clock>(mt) == gt);
+       assert(clock_cast<mil_clock>(gt) == mt);
+    }
+
+    // s2s -> mil
+    {
+       sys_days st(1997_y/dec/12);
+       auto mt = mil_clock::from_sys(st);
+       auto s2t = s2s_clock::from_sys(st);
+
+       //direct trait conversion
+       conversions = 0;
+       assert(clock_cast<mil_clock>(s2t) == mt);
+       assert(conversions == 1);
+
+       //uses sys_clock
+       conversions = 0;
+       assert(clock_cast<s2s_clock>(mt) == s2t);
+       assert(conversions == 2);
+    }
+}
diff --git a/third_party/date-3.0.1/test/clock_cast_test/deprecated.pass.cpp b/third_party/date-3.0.1/test/clock_cast_test/deprecated.pass.cpp
new file mode 100644
index 00000000..74d246e3
--- /dev/null
+++ b/third_party/date-3.0.1/test/clock_cast_test/deprecated.pass.cpp
@@ -0,0 +1,90 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2017 Tomasz Kamiński
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+#include "tz.h"
+#include <cassert>
+
+int
+main()
+{
+    using namespace date;
+
+    // sys <-> utc
+    {
+       sys_days st(1997_y/dec/12);
+       auto ut = utc_clock::from_sys(st);
+
+       assert(to_utc_time(st) == ut);
+       assert(to_sys_time(ut) == st);
+    }
+
+    // tai <-> utc
+    {
+       sys_days st(1997_y/dec/12);
+       auto ut = utc_clock::from_sys(st);
+       auto tt = tai_clock::from_utc(ut);
+
+       assert(to_tai_time(ut) == tt);
+       assert(to_utc_time(tt) == ut);
+    }
+
+    // tai <-> sys
+    {
+       sys_days st(1997_y/dec/12);
+       auto ut = utc_clock::from_sys(st);
+       auto tt = tai_clock::from_utc(ut);
+
+       assert(to_tai_time(st) == tt);
+       assert(to_sys_time(tt) == st);
+    }
+
+    // gps <-> utc
+    {
+       sys_days st(1997_y/dec/12);
+       auto ut = utc_clock::from_sys(st);
+       auto gt = gps_clock::from_utc(ut);
+
+       assert(to_gps_time(ut) == gt);
+       assert(to_utc_time(gt) == ut);
+    }
+
+    // gps <-> sys
+    {
+       sys_days st(1997_y/dec/12);
+       auto ut = utc_clock::from_sys(st);
+       auto gt = gps_clock::from_utc(ut);
+
+       assert(to_gps_time(st) == gt);
+       assert(to_sys_time(gt) == st);
+    }
+
+    // tai <-> gps
+    {
+       sys_days st(1997_y/dec/12);
+       auto ut = utc_clock::from_sys(st);
+       auto tt = tai_clock::from_utc(ut);
+       auto gt = gps_clock::from_utc(ut);
+
+       assert(to_gps_time(tt) == gt);
+       assert(to_tai_time(gt) == tt);
+    }
+}
diff --git a/third_party/date-3.0.1/test/clock_cast_test/local_t.pass.cpp b/third_party/date-3.0.1/test/clock_cast_test/local_t.pass.cpp
new file mode 100644
index 00000000..c80459d5
--- /dev/null
+++ b/third_party/date-3.0.1/test/clock_cast_test/local_t.pass.cpp
@@ -0,0 +1,132 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2018 Tomasz Kamiński
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+#include <chrono>
+#include "date/tz.h"
+
+int
+main()
+{
+   using namespace date;
+   using namespace std::chrono;
+
+   // self
+   {
+     auto ls = local_days{1970_y/January/1_d};
+     assert(clock_cast<local_t>(ls) == ls);
+   }
+
+   /// sys epoch
+   {
+     auto ls = local_days{1970_y/January/1_d};
+     auto st = clock_cast<system_clock>(ls);
+     assert(clock_cast<local_t>(st) == ls);
+     assert(st.time_since_epoch() == seconds(0));
+   }
+
+   /// sys 2000 case
+   {
+     auto ls = local_days{2000_y/January/1_d};
+     auto st = clock_cast<system_clock>(ls);
+     assert(clock_cast<local_t>(st) == ls);
+     assert(st.time_since_epoch() == seconds(946684800));
+   }
+
+   /// utc epoch
+   {
+     auto lu = local_days{1970_y/January/1_d};
+     auto ut = clock_cast<utc_clock>(lu);
+     assert(clock_cast<local_t>(ut) == lu);
+     assert(ut.time_since_epoch() == seconds(0));
+   }
+
+   // utc leap second
+   {
+     auto lu = local_days{2015_y/July/1_d} - milliseconds(1);
+     auto ut = clock_cast<utc_clock>(lu) + milliseconds(50); //into leap second
+
+     assert(clock_cast<local_t>(ut) == lu);
+   }
+
+   /// utc paper example
+   {
+     auto lu = local_days{2000_y/January/1_d};
+     auto ut = clock_cast<utc_clock>(lu);
+     assert(clock_cast<local_t>(ut) == lu);
+     assert(ut.time_since_epoch() == seconds(946684822));
+   }
+
+   /// tai epoch
+   {
+     auto lt = local_days{1958_y/January/1_d};
+     auto tt = clock_cast<tai_clock>(lt);
+     assert(clock_cast<local_t>(tt) == lt);
+     assert(tt.time_since_epoch() == seconds(0));
+
+     auto lu = local_days{1958_y/January/1_d} - seconds(10);
+     auto ut = clock_cast<utc_clock>(lu);
+     assert(clock_cast<tai_clock>(ut) == tt);
+   }
+
+   // tai paper example
+   {
+      auto lt = local_days{2000_y/January/1_d} + seconds(32);
+      auto tt = clock_cast<tai_clock>(lt);
+      assert(clock_cast<local_t>(tt) == lt);
+
+      auto lu = local_days{2000_y/January/1_d};
+      auto ut = clock_cast<utc_clock>(lu);
+      assert(clock_cast<tai_clock>(ut) == tt);
+   }
+
+   /// gps epoch
+   {
+     auto lg = local_days{1980_y/January/Sunday[1]};
+     auto gt = clock_cast<gps_clock>(lg);
+     assert(clock_cast<local_t>(gt) == lg);
+     assert(gt.time_since_epoch() == seconds(0));
+
+     auto lu = local_days{1980_y/January/Sunday[1]};
+     auto ut = clock_cast<utc_clock>(lu);
+     assert(clock_cast<gps_clock>(ut) == gt);
+
+     auto lt = local_days{1980_y/January/Sunday[1]} + seconds(19);
+     auto tt = clock_cast<tai_clock>(lt);
+     assert(clock_cast<gps_clock>(tt) == gt);
+   }
+
+   // gps 2000 example
+   {
+     auto lg = local_days{2000_y/January/1_d};
+     auto gt = clock_cast<gps_clock>(lg);
+     assert(clock_cast<local_t>(gt) == lg);
+
+     auto lu = local_days{2000_y/January/1_d} - seconds(13);
+     auto ut = clock_cast<utc_clock>(lu);
+     assert(clock_cast<gps_clock>(ut) == gt);
+
+     auto lt = local_days{2000_y/January/1_d} + seconds(19);
+     auto tt = clock_cast<tai_clock>(lt);
+     assert(clock_cast<gps_clock>(tt) == gt);
+   }
+
+}
diff --git a/third_party/date-3.0.1/test/clock_cast_test/noncastable.pass.cpp b/third_party/date-3.0.1/test/clock_cast_test/noncastable.pass.cpp
new file mode 100644
index 00000000..373f2237
--- /dev/null
+++ b/third_party/date-3.0.1/test/clock_cast_test/noncastable.pass.cpp
@@ -0,0 +1,251 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2017, 2018 Tomasz Kamiński
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+#include "tz.h"
+#include <type_traits>
+#include <cassert>
+
+template<typename SourceClock, typename DestClock, typename = void>
+struct is_clock_castable
+  : std::false_type
+{};
+
+template<typename SourceClock, typename DestClock>
+struct is_clock_castable<SourceClock, DestClock, decltype(date::clock_cast<DestClock>(typename SourceClock::time_point()), void())>
+  : std::true_type
+{};
+
+
+//Clock based on steady clock, not related to wall time (sys_clock/utc_clock)
+struct steady_based_clock
+{
+  using duration = std::chrono::steady_clock::duration;
+  using rep = duration::rep;
+  using period = duration::period;
+  using time_point = std::chrono::time_point<steady_based_clock, duration>;
+
+  static time_point now()
+  {
+    return time_point(std::chrono::steady_clock::now().time_since_epoch());
+  }
+};
+
+//Traits that allow conversion between steady_clock and steady_based clock
+//Does not use wall-time clocks as rally (sys/utc)
+namespace date
+{
+   template<>
+   struct clock_time_conversion<std::chrono::steady_clock, steady_based_clock>
+   {
+     template<typename Duration>
+     std::chrono::time_point<std::chrono::steady_clock, Duration>
+     operator()(std::chrono::time_point<steady_based_clock, Duration> const& tp) const
+     {
+       using res = std::chrono::time_point<std::chrono::steady_clock, Duration>;
+       return res(tp.time_since_epoch());
+     }
+   };
+
+   template<>
+   struct clock_time_conversion<steady_based_clock, std::chrono::steady_clock>
+   {
+     template<typename Duration>
+     std::chrono::time_point<steady_based_clock, Duration>
+     operator()(std::chrono::time_point<std::chrono::steady_clock, Duration> const& tp) const
+     {
+       using res = std::chrono::time_point<steady_based_clock, Duration>;
+       return res(tp.time_since_epoch());
+     }
+   };
+}
+
+//Ambigous clocks both providing to/from_sys and to/from_utc
+//They are mock_ups just returning zero time_point
+struct amb1_clock
+{
+   using duration = std::chrono::seconds;
+   using rep = duration::rep;
+   using period = duration::period;
+   using time_point = std::chrono::time_point<amb1_clock>;
+
+   static time_point now()
+   {
+     return {};
+   }
+
+   template<typename Duration>
+   static
+   std::chrono::time_point<std::chrono::system_clock, Duration>
+   to_sys(std::chrono::time_point<amb1_clock, Duration> const&)
+   {
+     return {};
+   }
+
+   template<typename Duration>
+   static
+   std::chrono::time_point<amb1_clock, Duration>
+   from_sys(std::chrono::time_point<std::chrono::system_clock, Duration> const&)
+   {
+     return {};
+   }
+
+   template<typename Duration>
+   static
+   std::chrono::time_point<date::utc_clock, Duration>
+   to_utc(std::chrono::time_point<amb1_clock, Duration> const&)
+   {
+     return {};
+   }
+
+   template<typename Duration>
+   static
+   std::chrono::time_point<amb1_clock, Duration>
+   from_utc(std::chrono::time_point<date::utc_clock, Duration> const&)
+   {
+     return {};
+   }
+};
+
+struct amb2_clock
+{
+   using duration = std::chrono::seconds;
+   using rep = duration::rep;
+   using period = duration::period;
+   using time_point = std::chrono::time_point<amb2_clock>;
+
+   static time_point now()
+   {
+     return {};
+   }
+
+   template<typename Duration>
+   static
+   std::chrono::time_point<std::chrono::system_clock, Duration>
+   to_sys(std::chrono::time_point<amb2_clock, Duration> const&)
+   {
+     return {};
+   }
+
+   template<typename Duration>
+   static
+   std::chrono::time_point<amb2_clock, Duration>
+   from_sys(std::chrono::time_point<std::chrono::system_clock, Duration> const&)
+   {
+     return {};
+   }
+
+   template<typename Duration>
+   static
+   std::chrono::time_point<date::utc_clock, Duration>
+   to_utc(std::chrono::time_point<amb2_clock, Duration> const&)
+   {
+     return {};
+   }
+
+   template<typename Duration>
+   static
+   std::chrono::time_point<amb2_clock, Duration>
+   from_utc(std::chrono::time_point<date::utc_clock, Duration> const&)
+   {
+     return {};
+   }
+};
+
+namespace date
+{
+   //Disambiguates that sys_clock is preffered
+   template<>
+   struct clock_time_conversion<amb1_clock, amb2_clock>
+   {
+     template<typename Duration>
+     std::chrono::time_point<amb1_clock, Duration>
+     operator()(std::chrono::time_point<amb2_clock, Duration> const& tp) const
+     {
+       return amb1_clock::from_sys(amb2_clock::to_sys(tp));
+     }
+   };
+}
+
+int
+main()
+{
+    using namespace date;
+    using namespace std::chrono;
+    using sys_clock = std::chrono::system_clock;
+
+    //steady_clock (must be different that sys_clock)
+    static_assert(is_clock_castable<steady_clock, steady_clock>::value, "steady_clock -> steady_clock");
+    static_assert(!is_clock_castable<steady_clock, local_t>::value, "steady_clock -> local_t");
+    static_assert(!is_clock_castable<local_t, steady_clock>::value, "local_t -> steady_clock");
+    static_assert(!is_clock_castable<steady_clock, sys_clock>::value, "steady_clock -> sys_clock");
+    static_assert(!is_clock_castable<sys_clock, steady_clock>::value, "sys_clock -> steady_clock");
+    static_assert(!is_clock_castable<steady_clock, utc_clock>::value, "steady_clock -> utc_clock");
+    static_assert(!is_clock_castable<utc_clock, steady_clock>::value, "utc_clock -> steady_clock");
+    static_assert(!is_clock_castable<steady_clock, tai_clock>::value, "steady_clock -> tai_clock");
+    static_assert(!is_clock_castable<tai_clock, steady_clock>::value, "tai_clock -> steady_clock");
+
+    //steady_based_clock (unrelated to sys_clock and utc_clocks)
+    static_assert(is_clock_castable<steady_based_clock, steady_based_clock>::value, "steady_based_clock -> steady_based_clock");
+    static_assert(!is_clock_castable<steady_based_clock, local_t>::value, "steady_based_clock -> local_t");
+    static_assert(!is_clock_castable<local_t, steady_based_clock>::value, "local_t -> steady_based_clock");
+    static_assert(!is_clock_castable<steady_based_clock, sys_clock>::value, "steady_based_clock -> sys_clock");
+    static_assert(!is_clock_castable<sys_clock, steady_based_clock>::value, "sys_clock -> steady_based_clock");
+    static_assert(!is_clock_castable<steady_based_clock, utc_clock>::value, "steady_based_clock -> utc_clock");
+    static_assert(!is_clock_castable<utc_clock, steady_based_clock>::value, "utc_clock -> steady_based_clock");
+    static_assert(!is_clock_castable<steady_based_clock, tai_clock>::value, "steady_based_clock -> tai_clock");
+    static_assert(!is_clock_castable<tai_clock, steady_based_clock>::value, "tai_clock -> steady_based_clock");
+
+    //steady_based <-> steady_clock
+    {
+      auto s1 = steady_clock::time_point(steady_clock::duration(200));
+      auto s2 = steady_based_clock::time_point(steady_based_clock::duration(200));
+
+      assert(clock_cast<steady_based_clock>(s1) == s2);
+      assert(clock_cast<steady_clock>(s2) == s1);
+    }
+
+    //ambX <-> sys/utc works as one rally can be used in each case, or one lead to quicker conversione
+    static_assert(is_clock_castable<amb1_clock, amb1_clock>::value, "amb1_clock -> amb1_clock");
+    static_assert(is_clock_castable<amb1_clock, sys_clock>::value, "amb1_clock -> sys_clock");
+    static_assert(is_clock_castable<sys_clock, amb1_clock>::value, "sys_clock -> amb1_clock");
+    static_assert(is_clock_castable<amb1_clock, utc_clock>::value, "amb1_clock -> utc_clock");
+    static_assert(is_clock_castable<utc_clock, amb1_clock>::value, "utc_clock -> amb1_clock");
+    static_assert(is_clock_castable<amb1_clock, tai_clock>::value, "amb1_clock -> tai_clock");
+    static_assert(is_clock_castable<tai_clock, amb1_clock>::value, "tai_clock -> amb1_clock");
+    static_assert(is_clock_castable<amb1_clock, tai_clock>::value, "amb1_clock -> tai_clock");
+    static_assert(is_clock_castable<gps_clock, amb1_clock>::value, "gps_clock -> amb1_clock");
+    static_assert(is_clock_castable<amb2_clock, amb2_clock>::value, "amb2_clock -> amb2_clock");
+    static_assert(is_clock_castable<amb2_clock, sys_clock>::value, "amb2_clock -> sys_clock");
+    static_assert(is_clock_castable<sys_clock, amb2_clock>::value, "sys_clock -> amb2_clock");
+    static_assert(is_clock_castable<amb2_clock, utc_clock>::value, "amb2_clock -> utc_clock");
+    static_assert(is_clock_castable<utc_clock, amb2_clock>::value, "utc_clock -> amb2_clock");
+    static_assert(is_clock_castable<amb2_clock, tai_clock>::value, "amb2_clock -> tai_clock");
+    static_assert(is_clock_castable<tai_clock, amb2_clock>::value, "tai_clock -> amb2_clock");
+    static_assert(is_clock_castable<amb2_clock, tai_clock>::value, "amb2_clock -> tai_clock");
+    static_assert(is_clock_castable<gps_clock, amb2_clock>::value, "gps_clock -> amb2_clock");
+
+    //amb1 -> amb2: ambigous because can either go trough sys_clock or utc_clock
+    static_assert(!is_clock_castable<amb1_clock, amb2_clock>::value, "amb1_clock -> amb2_clock");
+
+    //amb2 -> amb1: disambiguated via trait specialization
+    static_assert(is_clock_castable<amb2_clock, amb1_clock>::value, "amb2_clock -> amb1_clock");
+}
diff --git a/third_party/date-3.0.1/test/clock_cast_test/normal_clocks.pass.cpp b/third_party/date-3.0.1/test/clock_cast_test/normal_clocks.pass.cpp
new file mode 100644
index 00000000..525bc022
--- /dev/null
+++ b/third_party/date-3.0.1/test/clock_cast_test/normal_clocks.pass.cpp
@@ -0,0 +1,102 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2017 Tomasz Kamiński
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+#include "tz.h"
+#include <cassert>
+
+int
+main()
+{
+    using namespace date;
+    using sys_clock = std::chrono::system_clock;
+
+    // self
+    {
+       sys_days st(1997_y/dec/12);
+       auto ut = utc_clock::from_sys(st);
+       auto tt = tai_clock::from_utc(ut);
+
+       assert(clock_cast<sys_clock>(st) == st);
+       assert(clock_cast<utc_clock>(ut) == ut);
+       assert(clock_cast<tai_clock>(tt) == tt);
+    }
+
+    // sys <-> utc
+    {
+       sys_days st(1997_y/dec/12);
+       auto ut = utc_clock::from_sys(st);
+
+       assert(clock_cast<utc_clock>(st) == ut);
+       assert(clock_cast<sys_clock>(ut) == st);
+    }
+
+    // tai <-> utc
+    {
+       sys_days st(1997_y/dec/12);
+       auto ut = utc_clock::from_sys(st);
+       auto tt = tai_clock::from_utc(ut);
+
+       assert(clock_cast<tai_clock>(ut) == tt);
+       assert(clock_cast<utc_clock>(tt) == ut);
+    }
+
+    // tai <-> sys
+    {
+       sys_days st(1997_y/dec/12);
+       auto ut = utc_clock::from_sys(st);
+       auto tt = tai_clock::from_utc(ut);
+
+       assert(clock_cast<tai_clock>(st) == tt);
+       assert(clock_cast<sys_clock>(tt) == st);
+    }
+
+    // gps <-> utc
+    {
+       sys_days st(1997_y/dec/12);
+       auto ut = utc_clock::from_sys(st);
+       auto gt = gps_clock::from_utc(ut);
+
+       assert(clock_cast<gps_clock>(ut) == gt);
+       assert(clock_cast<utc_clock>(gt) == ut);
+    }
+
+    // gps <-> sys
+    {
+       sys_days st(1997_y/dec/12);
+       auto ut = utc_clock::from_sys(st);
+       auto gt = gps_clock::from_utc(ut);
+
+       assert(clock_cast<gps_clock>(st) == gt);
+       assert(clock_cast<sys_clock>(gt) == st);
+    }
+
+    // tai <-> gps
+    {
+       sys_days st(1997_y/dec/12);
+       auto ut = utc_clock::from_sys(st);
+       auto tt = tai_clock::from_utc(ut);
+       auto gt = gps_clock::from_utc(ut);
+
+       assert(clock_cast<gps_clock>(tt) == gt);
+       assert(clock_cast<tai_clock>(gt) == tt);
+    }
+}
diff --git a/third_party/date-3.0.1/test/clock_cast_test/to_sys_return_int.fail.cpp b/third_party/date-3.0.1/test/clock_cast_test/to_sys_return_int.fail.cpp
new file mode 100644
index 00000000..370c6827
--- /dev/null
+++ b/third_party/date-3.0.1/test/clock_cast_test/to_sys_return_int.fail.cpp
@@ -0,0 +1,49 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2017 Tomasz Kamiński
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+#include "tz.h"
+
+struct bad_clock
+{
+  using duration = std::chrono::system_clock::duration;
+  using rep = duration::rep;
+  using period = duration::period;
+  using time_point = std::chrono::time_point<bad_clock, duration>;
+
+  template<typename Duration>
+  static
+  int
+  to_sys(std::chrono::time_point<bad_clock, Duration> const& tp)
+  {
+    return tp.time_since_epoch().count();
+  }
+};
+
+int
+main()
+{
+    using namespace date;
+    using sys_clock = std::chrono::system_clock;
+
+    auto bt = bad_clock::time_point();
+    clock_cast<sys_clock>(bt);
+}
diff --git a/third_party/date-3.0.1/test/clock_cast_test/to_sys_return_reference.fail.cpp b/third_party/date-3.0.1/test/clock_cast_test/to_sys_return_reference.fail.cpp
new file mode 100644
index 00000000..5fae1652
--- /dev/null
+++ b/third_party/date-3.0.1/test/clock_cast_test/to_sys_return_reference.fail.cpp
@@ -0,0 +1,51 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2017 Tomasz Kamiński
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+#include "tz.h"
+
+struct bad_clock
+{
+  using duration = std::chrono::system_clock::duration;
+  using rep = duration::rep;
+  using period = duration::period;
+  using time_point = std::chrono::time_point<bad_clock, duration>;
+
+  template<typename Duration>
+  static
+  date::sys_time<Duration> const&
+  to_sys(std::chrono::time_point<bad_clock, Duration> const& tp)
+  {
+    static date::sys_time<Duration> val;
+    val = date::sys_time<Duration>(tp.time_since_epoch());
+    return val;
+  }
+};
+
+int
+main()
+{
+    using namespace date;
+    using sys_clock = std::chrono::system_clock;
+
+    auto bt = bad_clock::time_point();
+    clock_cast<sys_clock>(bt);
+}
diff --git a/third_party/date-3.0.1/test/clock_cast_test/to_sys_return_utc_time.fail.cpp b/third_party/date-3.0.1/test/clock_cast_test/to_sys_return_utc_time.fail.cpp
new file mode 100644
index 00000000..a3e715c0
--- /dev/null
+++ b/third_party/date-3.0.1/test/clock_cast_test/to_sys_return_utc_time.fail.cpp
@@ -0,0 +1,49 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2017, 2018 Tomasz Kamiński
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+#include "tz.h"
+
+struct bad_clock
+{
+  using duration = std::chrono::system_clock::duration;
+  using rep = duration::rep;
+  using period = duration::period;
+  using time_point = std::chrono::time_point<bad_clock, duration>;
+
+  template<typename Duration>
+  static
+  date::utc_time<Duration>
+  to_sys(std::chrono::time_point<bad_clock, Duration> const& tp)
+  {
+    return date::utc_time<Duration>(tp.time_since_epoch());
+  }
+};
+
+int
+main()
+{
+    using namespace date;
+    using sys_clock = std::chrono::system_clock;
+
+    auto bt = bad_clock::time_point();
+    clock_cast<sys_clock>(bt);
+}
diff --git a/third_party/date-3.0.1/test/date_test/day.pass.cpp b/third_party/date-3.0.1/test/date_test/day.pass.cpp
new file mode 100644
index 00000000..0dbdf688
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/day.pass.cpp
@@ -0,0 +1,143 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// class day
+// {
+//     unsigned char d_;
+// public:
+//     explicit constexpr day(unsigned d) noexcept;
+//
+//     day& operator++()    noexcept;
+//     day  operator++(int) noexcept;
+//     day& operator--()    noexcept;
+//     day  operator--(int) noexcept;
+//
+//     day& operator+=(const days& d) noexcept;
+//     day& operator-=(const days& d) noexcept;
+//
+//     constexpr explicit operator unsigned() const noexcept;
+//     constexpr bool ok() const noexcept;
+// };
+//
+// constexpr bool operator==(const day& x, const day& y) noexcept;
+// constexpr bool operator!=(const day& x, const day& y) noexcept;
+// constexpr bool operator< (const day& x, const day& y) noexcept;
+// constexpr bool operator> (const day& x, const day& y) noexcept;
+// constexpr bool operator<=(const day& x, const day& y) noexcept;
+// constexpr bool operator>=(const day& x, const day& y) noexcept;
+//
+// constexpr day  operator+(const day&  x, const days& y) noexcept;
+// constexpr day  operator+(const days& x, const day&  y) noexcept;
+// constexpr day  operator-(const day&  x, const days& y) noexcept;
+// constexpr days operator-(const day&  x, const day&  y) noexcept;
+//
+// constexpr day operator "" _d(unsigned long long d) noexcept;
+// std::ostream& operator<<(std::ostream& os, const day& d);
+
+#include "date.h"
+
+#include <cassert>
+#include <sstream>
+#include <type_traits>
+
+static_assert( std::is_trivially_destructible<date::day>{}, "");
+static_assert( std::is_default_constructible<date::day>{}, "");
+static_assert( std::is_trivially_copy_constructible<date::day>{}, "");
+static_assert( std::is_trivially_copy_assignable<date::day>{}, "");
+static_assert( std::is_trivially_move_constructible<date::day>{}, "");
+static_assert( std::is_trivially_move_assignable<date::day>{}, "");
+
+static_assert( std::is_nothrow_constructible<date::day, unsigned>{}, "");
+static_assert( std::is_nothrow_constructible<unsigned, date::day>{}, "");
+static_assert(!std::is_convertible<unsigned, date::day>{}, "");
+static_assert(!std::is_convertible<date::day, unsigned>{}, "");
+static_assert(static_cast<unsigned>(date::day{1}) == 1, "");
+
+static_assert(!date::day{0}.ok(), "");
+static_assert( date::day{1}.ok(), "");
+static_assert( date::day{2}.ok(), "");
+static_assert( date::day{3}.ok(), "");
+static_assert( date::day{29}.ok(), "");
+static_assert( date::day{30}.ok(), "");
+static_assert( date::day{31}.ok(), "");
+static_assert(!date::day{32}.ok(), "");
+
+int
+main()
+{
+    using namespace date;
+    static_assert(std::is_same<decltype(1_d), day>{}, "");
+
+    static_assert(1_d == day{1}, "");
+    static_assert(2_d == day{2}, "");
+
+    static_assert(  1_d == 1_d, "");
+    static_assert(!(1_d == 2_d), "");
+    static_assert(!(2_d == 1_d), "");
+
+    static_assert(!(1_d != 1_d), "");
+    static_assert(  1_d != 2_d, "");
+    static_assert(  2_d != 1_d, "");
+
+    static_assert(!(1_d <  1_d), "");
+    static_assert(  1_d <  2_d, "");
+    static_assert(!(2_d <  1_d), "");
+
+    static_assert(  1_d <= 1_d, "");
+    static_assert(  1_d <= 2_d, "");
+    static_assert(!(2_d <= 1_d), "");
+
+    static_assert(!(1_d >  1_d), "");
+    static_assert(!(1_d >  2_d), "");
+    static_assert(  2_d >  1_d, "");
+
+    static_assert(  1_d >= 1_d, "");
+    static_assert(!(1_d >= 2_d), "");
+    static_assert(  2_d >= 1_d, "");
+
+    static_assert(3_d + days{7} == 10_d, "");
+    static_assert(days{7} + 3_d == 10_d, "");
+    static_assert(3_d + weeks{1} == 10_d, "");
+    static_assert(weeks{1} + 3_d == 10_d, "");
+
+    static_assert(7_d - days{3} == 4_d, "");
+    static_assert(3_d - 7_d == days{-4}, "");
+    static_assert(25_d - 11_d == weeks{2}, "");
+
+    auto d = 1_d;
+    assert(++d == 2_d);
+    assert(d++ == 2_d);
+    assert(d == 3_d);
+    assert(d-- == 3_d);
+    assert(d == 2_d);
+    assert(--d == 1_d);
+    assert((d += days{2}) == 3_d);
+    assert((d -= days{2}) == 1_d);
+
+    std::ostringstream os;
+    os << d;
+    assert(os.str() == "01");
+    d += days{11};
+    os.str("");
+    os << d;
+    assert(os.str() == "12");
+}
diff --git a/third_party/date-3.0.1/test/date_test/daypday.fail.cpp b/third_party/date-3.0.1/test/date_test/daypday.fail.cpp
new file mode 100644
index 00000000..80a92c7e
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/daypday.fail.cpp
@@ -0,0 +1,32 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// day + day not allowed
+
+#include "date.h"
+
+int
+main()
+{
+    using namespace date;
+    auto x = 3_d + 7_d;
+}
diff --git a/third_party/date-3.0.1/test/date_test/daysmday.fail.cpp b/third_party/date-3.0.1/test/date_test/daysmday.fail.cpp
new file mode 100644
index 00000000..42db047a
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/daysmday.fail.cpp
@@ -0,0 +1,32 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// days - day not allowed
+
+#include "date.h"
+
+int
+main()
+{
+    using namespace date;
+    auto x = days{3} - 7_d;
+}
diff --git a/third_party/date-3.0.1/test/date_test/daysmweekday.fail.cpp b/third_party/date-3.0.1/test/date_test/daysmweekday.fail.cpp
new file mode 100644
index 00000000..05e8e4c9
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/daysmweekday.fail.cpp
@@ -0,0 +1,32 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// days - weekday not allowed
+
+#include "date.h"
+
+int
+main()
+{
+    using namespace date;
+    auto b = days{1} - sun;
+}
diff --git a/third_party/date-3.0.1/test/date_test/detail/decimal_format_seconds.pass.cpp b/third_party/date-3.0.1/test/date_test/detail/decimal_format_seconds.pass.cpp
new file mode 100644
index 00000000..cce6ae8f
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/detail/decimal_format_seconds.pass.cpp
@@ -0,0 +1,141 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2017 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// template <class Duration>
+// class decimal_format_seconds
+// {
+//     using CT = typename std::common_type<Duration, std::chrono::seconds>::type;
+//     using rep = typename CT::rep;
+// public:
+//     static unsigned constexpr width = detail::width<CT::period::den>::value < 19 ?
+//                                       detail::width<CT::period::den>::value : 6u;
+//     using precision = std::chrono::duration<rep,
+//                                             std::ratio<1, static_pow10<width>::value>>;
+// private:
+//     std::chrono::seconds s_;
+//     precision            sub_s_;
+// 
+// public:
+//     constexpr explicit decimal_format_seconds(const Duration& d) noexcept;
+// 
+//     constexpr std::chrono::seconds& seconds() noexcept;
+//     constexpr std::chrono::seconds seconds() const noexcept;
+//     constexpr precision subseconds() const noexcept;
+//     constexpr precision to_duration() const noexcept;
+// 
+//     template <class CharT, class Traits>
+//     friend
+//     std::basic_ostream<CharT, Traits>&
+//     operator<<(std::basic_ostream<CharT, Traits>& os, const decimal_format_seconds& x);
+// };
+
+#include "date.h"
+
+#include <cassert>
+#include <sstream>
+#include <type_traits>
+
+using fortnights = std::chrono::duration<date::weeks::rep,
+                                         date::detail::ratio_multiply<std::ratio<2>,
+                                                                      date::weeks::period>>;
+
+using microfortnights = std::chrono::duration<std::int64_t,
+                                              date::detail::ratio_multiply<fortnights::period,
+                                                                           std::micro>>;
+
+int
+main()
+{
+    using namespace date::detail;
+    using namespace std;
+    using namespace std::chrono;
+
+    {
+        using D = decimal_format_seconds<minutes>;
+        static_assert(is_same<D::precision, seconds>{}, "");
+        static_assert(D::width == 0, "");
+        D dfs{minutes{3}};
+        assert(dfs.seconds() == seconds{180});
+        assert(dfs.to_duration() == seconds{180});
+        ostringstream out;
+        out << dfs;
+        assert(out.str() == "180");
+    }
+    {
+        using D = decimal_format_seconds<seconds>;
+        static_assert(is_same<D::precision, seconds>{}, "");
+        static_assert(D::width == 0, "");
+        D dfs{seconds{3}};
+        assert(dfs.seconds() == seconds{3});
+        assert(dfs.to_duration() == seconds{3});
+        ostringstream out;
+        out << dfs;
+        assert(out.str() == "03");
+    }
+    {
+        using D = decimal_format_seconds<milliseconds>;
+        static_assert(D::width == 3, "");
+        D dfs{seconds{3}};
+        assert(dfs.seconds() == seconds{3});
+        assert(dfs.to_duration() == seconds{3});
+        assert(dfs.subseconds() == milliseconds{0});
+        ostringstream out;
+        out << dfs;
+        assert(out.str() == "03.000");
+    }
+    {
+        using D = decimal_format_seconds<milliseconds>;
+        static_assert(D::width == 3, "");
+        D dfs{milliseconds{3}};
+        assert(dfs.seconds() == seconds{0});
+        assert(dfs.to_duration() == milliseconds{3});
+        assert(dfs.subseconds() == milliseconds{3});
+        ostringstream out;
+        out << dfs;
+        assert(out.str() == "00.003");
+    }
+    {
+        using D = decimal_format_seconds<microfortnights>;
+        static_assert(D::width == 4, "");
+        D dfs{microfortnights{3}};
+        using S = D::precision;
+        assert(dfs.seconds() == seconds{3});
+        assert(dfs.to_duration() == S{36288});
+        assert(dfs.subseconds() == S{6288});
+        ostringstream out;
+        out << dfs;
+        assert(out.str() == "03.6288");
+    }
+    {
+        using CT = common_type<seconds, microfortnights>::type;
+        using D = decimal_format_seconds<CT>;
+        static_assert(D::width == 4, "");
+        D dfs{microfortnights{3}};
+        using S = D::precision;
+        assert(dfs.seconds() == seconds{3});
+        assert(dfs.to_duration() == S{36288});
+        assert(dfs.subseconds() == S{6288});
+        ostringstream out;
+        out << dfs;
+        assert(out.str() == "03.6288");
+    }
+}
diff --git a/third_party/date-3.0.1/test/date_test/detail/static_pow10.pass.cpp b/third_party/date-3.0.1/test/date_test/detail/static_pow10.pass.cpp
new file mode 100644
index 00000000..fe44fa42
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/detail/static_pow10.pass.cpp
@@ -0,0 +1,50 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2017 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// template <unsigned exp>
+// struct static_pow10
+// {
+//     static constepxr std::uint64_t value = ...;
+// };
+
+#include "date.h"
+
+#include <cassert>
+#include <sstream>
+#include <type_traits>
+
+int
+main()
+{
+    using namespace date::detail;
+    static_assert(static_pow10<0>::value ==  1, "");
+    static_assert(static_pow10<1>::value ==  10, "");
+    static_assert(static_pow10<2>::value ==  100, "");
+    static_assert(static_pow10<3>::value ==  1000, "");
+    static_assert(static_pow10<4>::value ==  10000, "");
+    static_assert(static_pow10<5>::value ==  100000, "");
+    static_assert(static_pow10<6>::value ==  1000000, "");
+    static_assert(static_pow10<7>::value ==  10000000, "");
+    static_assert(static_pow10<8>::value ==  100000000, "");
+    static_assert(static_pow10<9>::value ==  1000000000, "");
+    static_assert(static_pow10<10>::value == 10000000000, "");
+}
diff --git a/third_party/date-3.0.1/test/date_test/detail/width.pass.cpp b/third_party/date-3.0.1/test/date_test/detail/width.pass.cpp
new file mode 100644
index 00000000..94f57b7f
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/detail/width.pass.cpp
@@ -0,0 +1,64 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2017 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// width<n>::value is the number of fractional decimal digits in 1/n
+// width<0>::value and width<1>::value are defined to be 0
+// If 1/n takes more than 18 fractional decimal digits,
+//   the result is truncated to 19.
+// Example:  width<2>::value    ==  1
+// Example:  width<3>::value    == 19
+// Example:  width<4>::value    ==  2
+// Example:  width<10>::value   ==  1
+// Example:  width<1000>::value ==  3
+// template <std::uint64_t n>
+//
+// struct width
+// {
+//     static constexpr unsigned value = ...;
+// };
+
+#include "date.h"
+
+#include <cassert>
+#include <sstream>
+#include <type_traits>
+
+int
+main()
+{
+    using namespace date::detail;
+    static_assert(width<0, 1>::value == 0, "");
+    static_assert(width<1, 1>::value == 0, "");
+    static_assert(width<1, 2>::value == 1, "");
+    static_assert(width<1, 3>::value == 19, "");
+    static_assert(width<1, 4>::value == 2, "");
+    static_assert(width<1, 5>::value == 1, "");
+    static_assert(width<1, 6>::value == 19, "");
+    static_assert(width<1, 7>::value == 19, "");
+    static_assert(width<1, 8>::value == 3, "");
+    static_assert(width<1, 9>::value == 19, "");
+    static_assert(width<1, 10>::value == 1, "");
+    static_assert(width<1, 100>::value == 2, "");
+    static_assert(width<1, 1000>::value == 3, "");
+    static_assert(width<1, 10000>::value == 4, "");
+    static_assert(width<756, 625>::value == 4, "");
+}
diff --git a/third_party/date-3.0.1/test/date_test/durations.pass.cpp b/third_party/date-3.0.1/test/date_test/durations.pass.cpp
new file mode 100644
index 00000000..970ddde7
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/durations.pass.cpp
@@ -0,0 +1,62 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// durations
+//
+// using days = std::chrono::duration
+//     <int, std::ratio_multiply<std::ratio<24>, std::chrono::hours::period>>;
+//
+// using weeks = std::chrono::duration
+//     <int, std::ratio_multiply<std::ratio<7>, days::period>>;
+//
+// using years = std::chrono::duration
+//     <int, std::ratio_multiply<std::ratio<146097, 400>, days::period>>;
+//
+// using months = std::chrono::duration
+//     <int, std::ratio_divide<years::period, std::ratio<12>>>;
+//
+// time_point
+//
+// using sys_days = std::chrono::time_point<std::chrono::system_clock, days>;
+
+#include "date.h"
+
+#include <type_traits>
+
+static_assert(date::days{1} == std::chrono::hours{24}, "");
+
+static_assert(date::weeks{1} == date::days{7}, "");
+
+static_assert(date::months{12} == date::years{1}, "");
+static_assert(date::days{30} < date::months{1} && date::months{1} < date::days{31}, "");
+static_assert(date::weeks{4} < date::months{1} && date::months{1} < date::weeks{5}, "");
+
+static_assert(date::years{400} == date::days{146097}, "");
+static_assert(date::days{365} < date::years{1} && date::years{1} < date::days{366}, "");
+static_assert(date::weeks{52} < date::years{1} && date::years{1} < date::weeks{53}, "");
+
+static_assert(std::is_same<date::sys_days::duration, date::days>{}, "");
+
+int
+main()
+{
+}
diff --git a/third_party/date-3.0.1/test/date_test/durations_output.pass.cpp b/third_party/date-3.0.1/test/date_test/durations_output.pass.cpp
new file mode 100644
index 00000000..ebf3ff5e
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/durations_output.pass.cpp
@@ -0,0 +1,328 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2018 Tomasz Kamiński
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+
+#include "date.h"
+
+#include <cassert>
+#include <sstream>
+
+void test_SI()
+{
+   using namespace std::chrono;
+   using namespace date;
+
+   std::ostringstream os;
+
+   // atto
+   {
+     duration<int, std::atto> d(13);
+     os << d;
+     assert(os.str() == "13as");
+     os.str("");
+   }
+
+   // femto
+   {
+     duration<int, std::femto> d(13);
+     os << d;
+     assert(os.str() == "13fs");
+     os.str("");
+   }
+
+   // pico
+   {
+     duration<int, std::pico> d(13);
+     os << d;
+     assert(os.str() == "13ps");
+     os.str("");
+   }
+
+   // nano
+   {
+     duration<int, std::nano> d(13);
+     os << d;
+     assert(os.str() == "13ns");
+     os.str("");
+   }
+
+   // mikro
+   {
+     duration<int, std::micro> d(13);
+     os << d;
+     assert(os.str() == "13\xC2\xB5s");
+     os.str("");
+   }
+
+   // milli
+   {
+     duration<int, std::milli> d(13);
+     os << d;
+     assert(os.str() == "13ms");
+     os.str("");
+   }
+
+   // centi
+   {
+     duration<int, std::centi> d(13);
+     os << d;
+     assert(os.str() == "13cs");
+     os.str("");
+   }
+
+   // deci
+   {
+     duration<int, std::deci> d(13);
+     os << d;
+     assert(os.str() == "13ds");
+     os.str("");
+   }
+
+   // seconds
+   {
+     duration<int> d(13);
+     os << d;
+     assert(os.str() == "13s");
+     os.str("");
+   }
+
+   // deca
+   {
+     duration<int, std::deca> d(13);
+     os << d;
+     assert(os.str() == "13das");
+     os.str("");
+   }
+
+   // hecto
+   {
+     duration<int, std::hecto> d(13);
+     os << d;
+     assert(os.str() == "13hs");
+     os.str("");
+   }
+
+   // kilo
+   {
+     duration<int, std::kilo> d(13);
+     os << d;
+     assert(os.str() == "13ks");
+     os.str("");
+   }
+
+   // mega
+   {
+     duration<int, std::mega> d(13);
+     os << d;
+     assert(os.str() == "13Ms");
+     os.str("");
+   }
+
+   // giga
+   {
+     duration<int, std::giga> d(13);
+     os << d;
+     assert(os.str() == "13Gs");
+     os.str("");
+   }
+
+   // tera
+   {
+     duration<int, std::tera> d(13);
+     os << d;
+     assert(os.str() == "13Ts");
+     os.str("");
+   }
+
+   // peta
+   {
+     duration<int, std::peta> d(13);
+     os << d;
+     assert(os.str() == "13Ps");
+     os.str("");
+   }
+
+   // femto
+   {
+     duration<int, std::exa> d(13);
+     os << d;
+     assert(os.str() == "13Es");
+     os.str("");
+   }
+}
+
+void test_calendar()
+{
+   using namespace std::chrono;
+   using namespace date;
+
+   std::ostringstream os;
+
+   // minutes
+   {
+      minutes d(13);
+      os << d;
+      assert(os.str() == "13min");
+      os.str("");
+   }
+
+   // hours
+   {
+      hours d(13);
+      os << d;
+      assert(os.str() == "13h");
+      os.str("");
+   }
+
+   // days
+   {
+      days d(13);
+      os << d;
+      assert(os.str() == "13d");
+      os.str("");
+   }
+}
+
+void test_integral_scale()
+{
+   using namespace std::chrono;
+   using namespace date;
+
+   std::ostringstream os;
+
+   // ratio 123 / 1
+   {
+      duration<int, std::ratio<123, 1>> d(13);
+      os << d;
+      assert(os.str() == "13[123]s");
+      os.str("");
+   }
+
+   // ratio 100 / 4 = ratio 25 / 1
+   {
+      duration<int, std::ratio<25, 1>> d(13);
+      os << d;
+      assert(os.str() == "13[25]s");
+      os.str("");
+   }
+
+   // weeks = ratio 7 * 24 * 60 * 60 / 1 = ratio 604800 / 1
+   {
+      weeks d(13);
+      os << d;
+      assert(os.str() == "13[604800]s");
+      os.str("");
+   }
+
+   // years = 146097/400 days = ratio 146097/400 * 24 * 60 * 60 = ratio 31556952 / 1
+   {
+      years d(13);
+      os << d;
+      assert(os.str() == "13[31556952]s");
+      os.str("");
+   }
+
+   // months = 1/12 years = ratio 1/12 * 31556952  = ratio 2629746 / 1
+   {
+      months d(13);
+      os << d;
+      assert(os.str() == "13[2629746]s");
+      os.str("");
+   }
+}
+
+void test_ratio_scale()
+{
+   using namespace std::chrono;
+   using namespace date;
+
+   std::ostringstream os;
+
+   // ratio 1 / 2
+   {
+      duration<int, std::ratio<1, 2>> d(13);
+      os << d;
+      assert(os.str() == "13[1/2]s");
+      os.str("");
+   }
+
+   // ratio 100 / 3
+   {
+      duration<int, std::ratio<100, 3>> d(13);
+      os << d;
+      assert(os.str() == "13[100/3]s");
+      os.str("");
+   }
+
+   // ratio 100 / 6 = ratio 50 / 3
+   {
+      duration<int, std::ratio<100, 6>> d(13);
+      os << d;
+      assert(os.str() == "13[50/3]s");
+      os.str("");
+   }
+}
+
+void test_constexpr()
+{
+  using date::detail::get_units;
+
+  CONSTCD11 auto as = get_units<char>(std::atto{});
+  CONSTCD11 auto fs = get_units<char>(std::femto{});
+  CONSTCD11 auto ps = get_units<char>(std::pico{});
+  CONSTCD11 auto ns = get_units<char>(std::nano{});
+  CONSTCD11 auto us = get_units<char>(std::micro{});
+  CONSTCD11 auto usw = get_units<wchar_t>(std::micro{});
+  CONSTCD11 auto ms = get_units<char>(std::milli{});
+  CONSTCD11 auto cs = get_units<char>(std::centi{});
+  CONSTCD11 auto ds = get_units<char>(std::deci{});
+  CONSTCD11 auto s = get_units<char>(std::ratio<1>{});
+  CONSTCD11 auto das = get_units<char>(std::deca{});
+  CONSTCD11 auto hs = get_units<char>(std::hecto{});
+  CONSTCD11 auto ks = get_units<char>(std::kilo{});
+  CONSTCD11 auto Ms = get_units<char>(std::mega{});
+  CONSTCD11 auto Gs = get_units<char>(std::giga{});
+  CONSTCD11 auto Ts = get_units<char>(std::tera{});
+  CONSTCD11 auto Ps = get_units<char>(std::peta{});
+  CONSTCD11 auto Es = get_units<char>(std::exa{});
+  (void)as, (void)fs, (void)ps, (void)ns, (void)usw, (void)us,
+  (void)ms, (void)cs, (void)ds, (void)s,  (void)das, (void)hs,
+  (void)ks, (void)Ms, (void)Gs, (void)Ts, (void)Ps,  (void)Es;
+
+  CONSTCD11 auto min = get_units<char>(std::ratio<60>{});
+  CONSTCD11 auto h = get_units<char>(std::ratio<3600>{});
+  CONSTCD11 auto d = get_units<char>(std::ratio<86400>{});
+  (void)min, (void)h, (void)d;
+
+  CONSTCD14 auto integer = get_units<char>(std::ratio<123>{});
+  CONSTCD14 auto ratio = get_units<char>(std::ratio<123, 3>{});
+  (void)integer, (void)ratio;
+}
+
+int
+main()
+{
+  test_SI();
+  test_calendar();
+  test_integral_scale();
+  test_ratio_scale();
+}
diff --git a/third_party/date-3.0.1/test/date_test/format/century.pass.cpp b/third_party/date-3.0.1/test/date_test/format/century.pass.cpp
new file mode 100644
index 00000000..1b401f7b
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/format/century.pass.cpp
@@ -0,0 +1,117 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+#include "date.h"
+
+#include <cassert>
+#include <sstream>
+#include <type_traits>
+
+int
+main()
+{
+    using namespace date;
+    using namespace std::chrono;
+    std::ostringstream os;
+    os << format("%C", sys_days{jun/1/20001});
+    assert(os.str() == "200");
+
+    os.str("");
+    os << format("%C", sys_days{jun/1/20000});
+    assert(os.str() == "200");
+
+    os.str("");
+    os << format("%C", sys_days{jun/1/19999});
+    assert(os.str() == "199");
+
+    os.str("");
+    os << format("%C", sys_days{jun/1/2001});
+    assert(os.str() == "20");
+
+    os.str("");
+    os << format("%C", sys_days{jun/1/2000});
+    assert(os.str() == "20");
+
+    os.str("");
+    os << format("%C", sys_days{jun/1/1999});
+    assert(os.str() == "19");
+
+    os.str("");
+    os << format("%C", sys_days{jun/1/101});
+    assert(os.str() == "01");
+
+    os.str("");
+    os << format("%C", sys_days{jun/1/100});
+    assert(os.str() == "01");
+
+    os.str("");
+    os << format("%C", sys_days{jun/1/99});
+    assert(os.str() == "00");
+
+    os.str("");
+    os << format("%C", sys_days{jun/1/1});
+    assert(os.str() == "00");
+
+    os.str("");
+    os << format("%C", sys_days{jun/1/0});
+    assert(os.str() == "00");
+
+    os.str("");
+    os << format("%C", sys_days{jun/1/-1});
+    assert(os.str() == "-01");
+
+    os.str("");
+    os << format("%C", sys_days{jun/1/-99});
+    assert(os.str() == "-01");
+
+    os.str("");
+    os << format("%C", sys_days{jun/1/-100});
+    assert(os.str() == "-01");
+
+    os.str("");
+    os << format("%C", sys_days{jun/1/-101});
+    assert(os.str() == "-02");
+
+    os.str("");
+    os << format("%C", sys_days{jun/1/-1999});
+    assert(os.str() == "-20");
+
+    os.str("");
+    os << format("%C", sys_days{jun/1/-2000});
+    assert(os.str() == "-20");
+
+    os.str("");
+    os << format("%C", sys_days{jun/1/-2001});
+    assert(os.str() == "-21");
+
+    os.str("");
+    os << format("%C", sys_days{jun/1/-19999});
+    assert(os.str() == "-200");
+
+    os.str("");
+    os << format("%C", sys_days{jun/1/-20000});
+    assert(os.str() == "-200");
+
+    os.str("");
+    os << format("%C", sys_days{jun/1/-20001});
+    assert(os.str() == "-201");
+}
diff --git a/third_party/date-3.0.1/test/date_test/format/misc.pass.cpp b/third_party/date-3.0.1/test/date_test/format/misc.pass.cpp
new file mode 100644
index 00000000..06deb241
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/format/misc.pass.cpp
@@ -0,0 +1,52 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+#include "date.h"
+#include <cassert>
+#include <sstream>
+
+template <class T>
+void
+test(const std::string& in_fmt, const std::string& input,
+     const std::string& out_fmt, const std::string& output)
+{
+    using namespace date;
+    std::istringstream in{input};
+    T t;
+    in >> parse(in_fmt, t);
+    assert(!in.fail());
+    auto s = format(out_fmt, t);
+    assert(s == output);
+}
+
+int
+main()
+{
+    using namespace date;
+    test<year>("%Y", "2017", "%Y", "2017");
+    test<month>("%m", "3", "%m", "03");
+    test<day>("%d", "25", "%d", "25");
+    test<year_month>("%Y-%m", "2017-03", "%Y-%m", "2017-03");
+    test<year_month>("%y%m", "1703", "%Y-%m", "2017-03");
+    test<month_day>("%m/%d", "3/25", "%m/%d", "03/25");
+    test<weekday>("%w", "3", "%w", "3");
+}
diff --git a/third_party/date-3.0.1/test/date_test/format/range.pass.cpp b/third_party/date-3.0.1/test/date_test/format/range.pass.cpp
new file mode 100644
index 00000000..fbe2d8c6
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/format/range.pass.cpp
@@ -0,0 +1,78 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+#include "date.h"
+
+#include <cassert>
+#include <sstream>
+#include <type_traits>
+
+using fortnights = std::chrono::duration<date::weeks::rep,
+                                         date::detail::ratio_multiply<std::ratio<2>,
+                                                                      date::weeks::period>>;
+
+using microfortnights = std::chrono::duration<std::int64_t,
+                                              date::detail::ratio_multiply<fortnights::period,
+                                                                           std::micro>>;
+
+int
+main()
+{
+    using namespace date;
+    using namespace std::chrono;
+    std::ostringstream os;
+    os << format("%F %T", sys_days{jan/1/year::min()});
+    assert(os.str() == "-32767-01-01 00:00:00");
+    os.str("");
+    os << format("%F %T", sys_days{dec/last/year::max()});
+    assert(os.str() == "32767-12-31 00:00:00");
+    os.str("");
+    os << format("%F %T", sys_days{dec/last/year::max()} + hours{23} + minutes{59} +
+                                                  seconds{59} + microseconds{999999});
+    assert(os.str() == "32767-12-31 23:59:59.999999");
+    os.str("");
+
+    os << format("%Y-%m-%d %H:%M:%S", sys_days{jan/1/year::min()});
+    assert(os.str() == "-32767-01-01 00:00:00");
+    os.str("");
+    os << format("%Y-%m-%d %H:%M:%S", sys_days{dec/last/year::max()});
+    assert(os.str() == "32767-12-31 00:00:00");
+    os.str("");
+    os << format("%Y-%m-%d %H:%M:%S", sys_days{dec/last/year::max()} + hours{23} +
+                                        minutes{59} + seconds{59} + microseconds{999999});
+    assert(os.str() == "32767-12-31 23:59:59.999999");
+    os.str("");
+
+    os << format("%F %T", sys_days{jan/1/year::min()} + microfortnights{1});
+    assert(os.str() == "-32767-01-01 00:00:01.2096");
+    os.str("");
+    os << format("%F %T", sys_days{dec/last/year::max()} + microfortnights{1});
+    assert(os.str() == "32767-12-31 00:00:01.2096");
+    os.str("");
+
+    os << format("%F", jan/1/year::min());
+    assert(os.str() == "-32767-01-01");
+    os.str("");
+    os << format("%F", dec/last/year::max());
+    assert(os.str() == "32767-12-31");
+    os.str("");
+}
diff --git a/third_party/date-3.0.1/test/date_test/format/two_dight_year.pass.cpp b/third_party/date-3.0.1/test/date_test/format/two_dight_year.pass.cpp
new file mode 100644
index 00000000..3f615b32
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/format/two_dight_year.pass.cpp
@@ -0,0 +1,121 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+#include "date.h"
+
+#include <cassert>
+#include <sstream>
+#include <type_traits>
+
+int
+main()
+{
+    using namespace date;
+    using namespace std::chrono;
+    std::ostringstream os;
+    os << format("%y", sys_days{jun/1/20001});
+    assert(os.str() == "01");
+
+    os.str("");
+    os << format("%y", sys_days{jun/1/20000});
+    assert(os.str() == "00");
+
+    os.str("");
+    os << format("%y", sys_days{jun/1/19999});
+    assert(os.str() == "99");
+
+    os.str("");
+    os << format("%y", sys_days{jun/1/2001});
+    assert(os.str() == "01");
+
+    os.str("");
+    os << format("%y", sys_days{jun/1/2000});
+    assert(os.str() == "00");
+
+    os.str("");
+    os << format("%y", sys_days{jun/1/1999});
+    assert(os.str() == "99");
+
+    os.str("");
+    os << format("%y", sys_days{jun/1/101});
+    assert(os.str() == "01");
+
+    os.str("");
+    os << format("%y", sys_days{jun/1/100});
+    assert(os.str() == "00");
+
+    os.str("");
+    os << format("%y", sys_days{jun/1/99});
+    assert(os.str() == "99");
+
+    os.str("");
+    os << format("%y", sys_days{jun/1/1});
+    assert(os.str() == "01");
+
+    os.str("");
+    os << format("%y", sys_days{jun/1/0});
+    assert(os.str() == "00");
+
+    os.str("");
+    os << format("%y", sys_days{jun/1/-1});
+    assert(os.str() == "01");
+
+    os.str("");
+    os << format("%y", sys_days{jun/1/-99});
+    assert(os.str() == "99");
+
+    os.str("");
+    os << format("%y", sys_days{jun/1/-100});
+    assert(os.str() == "00");
+
+    os.str("");
+    os << format("%y", sys_days{jun/1/-101});
+    assert(os.str() == "01");
+
+    os.str("");
+    os << format("%y", sys_days{jun/1/-1999});
+    assert(os.str() == "99");
+
+    os.str("");
+    os << format("%y", sys_days{jun/1/-2000});
+    assert(os.str() == "00");
+
+    os.str("");
+    os << format("%y", sys_days{jun/1/-2001});
+    assert(os.str() == "01");
+
+    os.str("");
+    os << format("%y", sys_days{jun/1/-19999});
+    assert(os.str() == "99");
+
+    os.str("");
+    os << format("%y", sys_days{jun/1/-20000});
+    assert(os.str() == "00");
+
+    os.str("");
+    os << format("%y", sys_days{jun/1/-20001});
+    assert(os.str() == "01");
+
+    os.str("");
+    os << format("%y", sys_days{jun/1/year::min()});
+    assert(os.str() == "67");
+}
diff --git a/third_party/date-3.0.1/test/date_test/last.pass.cpp b/third_party/date-3.0.1/test/date_test/last.pass.cpp
new file mode 100644
index 00000000..11b991c6
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/last.pass.cpp
@@ -0,0 +1,34 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// constexpr struct last_spec {} last{};
+
+#include "date.h"
+
+#include <type_traits>
+
+static_assert(std::is_same<decltype(date::last), const date::last_spec>{}, "");
+
+int
+main()
+{
+}
diff --git a/third_party/date-3.0.1/test/date_test/make_time.pass.cpp b/third_party/date-3.0.1/test/date_test/make_time.pass.cpp
new file mode 100644
index 00000000..f203807c
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/make_time.pass.cpp
@@ -0,0 +1,81 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// template <class Rep, class Period,
+//           class = typename std::enable_if
+//               <!std::chrono::treat_as_floating_point<Rep>::value>::type>
+// constexpr
+// time_of_day<std::chrono::duration<Rep, Period>>
+// make_time(std::chrono::duration<Rep, Period> d) noexcept;
+
+#include "date.h"
+
+#include <cassert>
+#include <type_traits>
+
+int
+main()
+{
+    using namespace date;
+    using namespace std;
+    using namespace std::chrono;
+
+    {
+        static_assert(is_same<decltype(make_time(nanoseconds{18429000000022})),
+                              time_of_day<nanoseconds>>{}, "");
+        auto tod = make_time(nanoseconds{18429000000022});
+        assert(tod.hours() == hours{5});
+        assert(tod.minutes() == minutes{7});
+        assert(tod.seconds() == seconds{9});
+        assert(tod.subseconds() == nanoseconds{22});
+    }
+    {
+        static_assert(is_same<decltype(make_time(microseconds{18429000022})),
+                              time_of_day<microseconds>>{}, "");
+        auto tod = make_time(microseconds{18429000022});
+        assert(tod.hours() == hours{5});
+        assert(tod.minutes() == minutes{7});
+        assert(tod.seconds() == seconds{9});
+        assert(tod.subseconds() == microseconds{22});
+    }
+    {
+        static_assert(is_same<decltype(make_time(seconds{18429})),
+                              time_of_day<seconds>>{}, "");
+        auto tod = make_time(seconds{18429});
+        assert(tod.hours() == hours{5});
+        assert(tod.minutes() == minutes{7});
+        assert(tod.seconds() == seconds{9});
+    }
+    {
+        static_assert(is_same<decltype(make_time(minutes{307})),
+                              time_of_day<minutes>>{}, "");
+        auto tod = make_time(minutes{307});
+        assert(tod.hours() == hours{5});
+        assert(tod.minutes() == minutes{7});
+    }
+    {
+        static_assert(is_same<decltype(make_time(hours{5})),
+                              time_of_day<hours>>{}, "");
+        auto tod = make_time(hours{5});
+        assert(tod.hours() == hours{5});
+    }
+}
diff --git a/third_party/date-3.0.1/test/date_test/month.pass.cpp b/third_party/date-3.0.1/test/date_test/month.pass.cpp
new file mode 100644
index 00000000..4dffa6bd
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/month.pass.cpp
@@ -0,0 +1,181 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// class month
+// {
+//     unsigned char m_;
+// public:
+//     explicit constexpr month(unsigned m) noexcept;
+//
+//     month& operator++()    noexcept;
+//     month  operator++(int) noexcept;
+//     month& operator--()    noexcept;
+//     month  operator--(int) noexcept;
+//
+//     month& operator+=(const months& m) noexcept;
+//     month& operator-=(const months& m) noexcept;
+//
+//     constexpr explicit operator unsigned() const noexcept;
+//     constexpr bool ok() const noexcept;
+// };
+//
+// constexpr bool operator==(const month& x, const month& y) noexcept;
+// constexpr bool operator!=(const month& x, const month& y) noexcept;
+// constexpr bool operator< (const month& x, const month& y) noexcept;
+// constexpr bool operator> (const month& x, const month& y) noexcept;
+// constexpr bool operator<=(const month& x, const month& y) noexcept;
+// constexpr bool operator>=(const month& x, const month& y) noexcept;
+//
+// constexpr month  operator+(const month&  x, const months& y) noexcept;
+// constexpr month  operator+(const months& x,  const month& y) noexcept;
+// constexpr month  operator-(const month&  x, const months& y) noexcept;
+// constexpr months operator-(const month&  x,  const month& y) noexcept;
+//
+// std::ostream& operator<<(std::ostream& os, const month& m);
+
+// constexpr month jan{1};
+// constexpr month feb{2};
+// constexpr month mar{3};
+// constexpr month apr{4};
+// constexpr month may{5};
+// constexpr month jun{6};
+// constexpr month jul{7};
+// constexpr month aug{8};
+// constexpr month sep{9};
+// constexpr month oct{10};
+// constexpr month nov{11};
+// constexpr month dec{12};
+
+#include "date.h"
+
+#include <cassert>
+#include <sstream>
+#include <type_traits>
+
+static_assert( std::is_trivially_destructible<date::month>{}, "");
+static_assert( std::is_default_constructible<date::month>{}, "");
+static_assert( std::is_trivially_copy_constructible<date::month>{}, "");
+static_assert( std::is_trivially_copy_assignable<date::month>{}, "");
+static_assert( std::is_trivially_move_constructible<date::month>{}, "");
+static_assert( std::is_trivially_move_assignable<date::month>{}, "");
+
+static_assert( std::is_nothrow_constructible<date::month, unsigned>{}, "");
+static_assert( std::is_nothrow_constructible<unsigned, date::month>{}, "");
+static_assert(!std::is_convertible<unsigned, date::month>{}, "");
+static_assert(!std::is_convertible<date::month, unsigned>{}, "");
+static_assert(static_cast<unsigned>(date::month{1}) == 1, "");
+
+static_assert(!date::month{0}.ok(), "");
+static_assert( date::month{1}.ok(), "");
+static_assert( date::month{2}.ok(), "");
+static_assert( date::month{3}.ok(), "");
+static_assert( date::month{4}.ok(), "");
+static_assert( date::month{5}.ok(), "");
+static_assert( date::month{6}.ok(), "");
+static_assert( date::month{7}.ok(), "");
+static_assert( date::month{8}.ok(), "");
+static_assert( date::month{9}.ok(), "");
+static_assert( date::month{10}.ok(), "");
+static_assert( date::month{11}.ok(), "");
+static_assert( date::month{12}.ok(), "");
+static_assert(!date::month{13}.ok(), "");
+
+int
+main()
+{
+    using namespace date;
+
+    static_assert(jan == month{1}, "");
+    static_assert(feb == month{2}, "");
+    static_assert(mar == month{3}, "");
+    static_assert(apr == month{4}, "");
+    static_assert(may == month{5}, "");
+    static_assert(jun == month{6}, "");
+    static_assert(jul == month{7}, "");
+    static_assert(aug == month{8}, "");
+    static_assert(sep == month{9}, "");
+    static_assert(oct == month{10}, "");
+    static_assert(nov == month{11}, "");
+    static_assert(dec == month{12}, "");
+
+    static_assert(!(jan != jan), "");
+    static_assert(  jan != feb, "");
+    static_assert(  feb != jan, "");
+
+    static_assert(!(jan <  jan), "");
+    static_assert(  jan <  feb, "");
+    static_assert(!(feb <  jan), "");
+
+    static_assert(  jan <= jan, "");
+    static_assert(  jan <= feb, "");
+    static_assert(!(feb <= jan), "");
+
+    static_assert(!(jan >  jan), "");
+    static_assert(!(jan >  feb), "");
+    static_assert(  feb >  jan, "");
+
+    static_assert(  jan >= jan, "");
+    static_assert(!(jan >= feb), "");
+    static_assert(  feb >= jan, "");
+
+    assert(mar + months{7} == oct);
+    assert(mar + months{27} == jun);
+    assert(months{7} + mar == oct);
+    assert(months{27} + mar == jun);
+
+    assert(mar - months{7} == aug);
+    assert(mar - months{27} == dec);
+
+    assert(mar - feb == months{1});
+    assert(feb - mar == months{11});
+
+#if __cplusplus >= 201402
+    static_assert(mar + months{7} == oct, "");
+    static_assert(mar + months{27} == jun, "");
+    static_assert(months{7} + mar == oct, "");
+    static_assert(months{27} + mar == jun, "");
+
+    static_assert(mar - months{7} == aug, "");
+    static_assert(mar - months{27} == dec, "");
+
+    static_assert(mar - feb == months{1}, "");
+    static_assert(feb - mar == months{11}, "");
+#endif
+
+    auto m = dec;
+    assert(++m == jan);
+    assert(m++ == jan);
+    assert(m == feb);
+    assert(m-- == feb);
+    assert(m == jan);
+    assert(--m == dec);
+    assert((m += months{2}) == feb);
+    assert((m -= months{2}) == dec);
+
+    std::ostringstream os;
+    os << m;
+    assert(os.str() == "Dec");
+    m += months{11};
+    os.str("");
+    os << m;
+    assert(os.str() == "Nov");
+}
diff --git a/third_party/date-3.0.1/test/date_test/month_day.pass.cpp b/third_party/date-3.0.1/test/date_test/month_day.pass.cpp
new file mode 100644
index 00000000..5fca9b26
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/month_day.pass.cpp
@@ -0,0 +1,82 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// class month_day
+// {
+// public:
+//     constexpr month_day(const date::month& m, const date::day& d) noexcept;
+//
+//     constexpr date::month month() const noexcept;
+//     constexpr date::day   day() const noexcept;
+//
+//     constexpr bool ok() const noexcept;
+// };
+
+// constexpr bool operator==(const month_day& x, const month_day& y) noexcept;
+// constexpr bool operator!=(const month_day& x, const month_day& y) noexcept;
+// constexpr bool operator< (const month_day& x, const month_day& y) noexcept;
+// constexpr bool operator> (const month_day& x, const month_day& y) noexcept;
+// constexpr bool operator<=(const month_day& x, const month_day& y) noexcept;
+// constexpr bool operator>=(const month_day& x, const month_day& y) noexcept;
+
+// std::ostream& operator<<(std::ostream& os, const month_day& md);
+
+#include "date.h"
+
+#include <cassert>
+#include <sstream>
+#include <type_traits>
+
+static_assert( std::is_trivially_destructible<date::month_day>{}, "");
+static_assert( std::is_default_constructible<date::month_day>{}, "");
+static_assert( std::is_trivially_copy_constructible<date::month_day>{}, "");
+static_assert( std::is_trivially_copy_assignable<date::month_day>{}, "");
+static_assert( std::is_trivially_move_constructible<date::month_day>{}, "");
+static_assert( std::is_trivially_move_assignable<date::month_day>{}, "");
+
+static_assert(std::is_nothrow_constructible<date::month_day, date::month,
+                                                             date::day>{}, "");
+
+int
+main()
+{
+    using namespace date;
+
+    constexpr month_day md1 = {feb, day{28}};
+    constexpr month_day md2 = {mar, day{1}};
+#if __cplusplus >= 201402
+    static_assert(md1.ok(), "");
+    static_assert(md2.ok(), "");
+    static_assert(!month_day{feb, day{32}}.ok(), "");
+    static_assert(!month_day{month{0}, day{1}}.ok(), "");
+#endif
+    static_assert(md1.month() == feb, "");
+    static_assert(md1.day() == day{28}, "");
+    static_assert(md2.month() == mar, "");
+    static_assert(md2.day() == day{1}, "");
+    static_assert(md1 == md1, "");
+    static_assert(md1 != md2, "");
+    static_assert(md1 < md2, "");
+    std::ostringstream os;
+    os << md1;
+    assert(os.str() == "Feb/28");
+}
diff --git a/third_party/date-3.0.1/test/date_test/month_day_last.pass.cpp b/third_party/date-3.0.1/test/date_test/month_day_last.pass.cpp
new file mode 100644
index 00000000..d458aeeb
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/month_day_last.pass.cpp
@@ -0,0 +1,75 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// class month_day_last
+// {
+// public:
+//     constexpr explicit month_day_last(const date::month& m) noexcept;
+//
+//     constexpr date::month month() const noexcept;
+//     constexpr bool ok() const noexcept;
+// };
+
+// constexpr bool operator==(const month_day_last& x, const month_day_last& y) noexcept;
+// constexpr bool operator!=(const month_day_last& x, const month_day_last& y) noexcept;
+// constexpr bool operator< (const month_day_last& x, const month_day_last& y) noexcept;
+// constexpr bool operator> (const month_day_last& x, const month_day_last& y) noexcept;
+// constexpr bool operator<=(const month_day_last& x, const month_day_last& y) noexcept;
+// constexpr bool operator>=(const month_day_last& x, const month_day_last& y) noexcept;
+
+// std::ostream& operator<<(std::ostream& os, const month_day_last& mdl);
+
+#include "date.h"
+
+#include <cassert>
+#include <sstream>
+#include <type_traits>
+
+static_assert( std::is_trivially_destructible<date::month_day_last>{}, "");
+static_assert(!std::is_default_constructible<date::month_day_last>{}, "");
+static_assert( std::is_trivially_copy_constructible<date::month_day_last>{}, "");
+static_assert( std::is_trivially_copy_assignable<date::month_day_last>{}, "");
+static_assert( std::is_trivially_move_constructible<date::month_day_last>{}, "");
+static_assert( std::is_trivially_move_assignable<date::month_day_last>{}, "");
+
+static_assert(std::is_nothrow_constructible<date::month_day_last, date::month>{}, "");
+static_assert(!std::is_convertible<date::month, date::month_day_last>{}, "");
+
+int
+main()
+{
+    using namespace date;
+
+    constexpr month_day_last mdl1{feb};
+    constexpr month_day_last mdl2{mar};
+    static_assert(mdl1.ok(), "");
+    static_assert(mdl2.ok(), "");
+    static_assert(!month_day_last{month{0}}.ok(), "");
+    static_assert(mdl1.month() == feb, "");
+    static_assert(mdl2.month() == mar, "");
+    static_assert(mdl1 == mdl1, "");
+    static_assert(mdl1 != mdl2, "");
+    static_assert(mdl1 < mdl2, "");
+    std::ostringstream os;
+    os << mdl1;
+    assert(os.str() == "Feb/last");
+}
diff --git a/third_party/date-3.0.1/test/date_test/month_weekday.pass.cpp b/third_party/date-3.0.1/test/date_test/month_weekday.pass.cpp
new file mode 100644
index 00000000..e059d2b8
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/month_weekday.pass.cpp
@@ -0,0 +1,77 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// class month_weekday
+// {
+// public:
+//     constexpr month_weekday(const date::month& m,
+//                               const date::weekday_indexed& wdi) noexcept;
+//
+//     constexpr date::month           month()           const noexcept;
+//     constexpr date::weekday_indexed weekday_indexed() const noexcept;
+//
+//     constexpr bool ok() const noexcept;
+// };
+
+// constexpr bool operator==(const month_weekday& x, const month_weekday& y) noexcept;
+// constexpr bool operator!=(const month_weekday& x, const month_weekday& y) noexcept;
+
+// std::ostream& operator<<(std::ostream& os, const month_weekday& mwd);
+
+#include "date.h"
+
+#include <cassert>
+#include <sstream>
+#include <type_traits>
+
+static_assert( std::is_trivially_destructible<date::month_weekday>{}, "");
+static_assert(!std::is_default_constructible<date::month_weekday>{}, "");
+static_assert( std::is_trivially_copy_constructible<date::month_weekday>{}, "");
+static_assert( std::is_trivially_copy_assignable<date::month_weekday>{}, "");
+static_assert( std::is_trivially_move_constructible<date::month_weekday>{}, "");
+static_assert( std::is_trivially_move_assignable<date::month_weekday>{}, "");
+
+static_assert(std::is_nothrow_constructible<date::month_weekday,
+                                                date::month,
+                                                date::weekday_indexed>{}, "");
+
+int
+main()
+{
+    using namespace date;
+
+    constexpr month_weekday mwd1 = {feb, sat[4]};
+    constexpr month_weekday mwd2 = {mar, mon[1]};
+    static_assert(mwd1.ok(), "");
+    static_assert(mwd2.ok(), "");
+    static_assert(!month_weekday{feb, sat[0]}.ok(), "");
+    static_assert(!month_weekday{month{0}, sun[1]}.ok(), "");
+    static_assert(mwd1.month() == feb, "");
+    static_assert(mwd1.weekday_indexed() == sat[4], "");
+    static_assert(mwd2.month() == mar, "");
+    static_assert(mwd2.weekday_indexed() == mon[1], "");
+    static_assert(mwd1 == mwd1, "");
+    static_assert(mwd1 != mwd2, "");
+    std::ostringstream os;
+    os << mwd1;
+    assert(os.str() == "Feb/Sat[4]");
+}
diff --git a/third_party/date-3.0.1/test/date_test/month_weekday_last.pass.cpp b/third_party/date-3.0.1/test/date_test/month_weekday_last.pass.cpp
new file mode 100644
index 00000000..4964d5e1
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/month_weekday_last.pass.cpp
@@ -0,0 +1,77 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// class month_weekday_last
+// {
+// public:
+//     constexpr month_weekday_last(const date::month& m,
+//                                  const date::weekday_last& wdl) noexcept;
+//
+//     constexpr date::month        month()        const noexcept;
+//     constexpr date::weekday_last weekday_last() const noexcept;
+//
+//     constexpr bool ok() const noexcept;
+// };
+
+// constexpr
+//     bool operator==(const month_weekday_last& x, const month_weekday_last& y) noexcept;
+// constexpr
+//     bool operator!=(const month_weekday_last& x, const month_weekday_last& y) noexcept;
+
+// std::ostream& operator<<(std::ostream& os, const month_weekday_last& mwdl);
+
+#include "date.h"
+
+#include <cassert>
+#include <sstream>
+#include <type_traits>
+
+static_assert( std::is_trivially_destructible<date::month_weekday_last>{}, "");
+static_assert(!std::is_default_constructible<date::month_weekday_last>{}, "");
+static_assert( std::is_trivially_copy_constructible<date::month_weekday_last>{}, "");
+static_assert( std::is_trivially_copy_assignable<date::month_weekday_last>{}, "");
+static_assert( std::is_trivially_move_constructible<date::month_weekday_last>{}, "");
+static_assert( std::is_trivially_move_assignable<date::month_weekday_last>{}, "");
+
+static_assert(std::is_nothrow_constructible<date::month_weekday_last,
+                                                date::month, date::weekday_last>{}, "");
+
+int
+main()
+{
+    using namespace date;
+
+    constexpr month_weekday_last mwdl1 = {feb, sat[last]};
+    constexpr month_weekday_last mwdl2 = {mar, mon[last]};
+    static_assert(mwdl1.ok(), "");
+    static_assert(mwdl2.ok(), "");
+    static_assert(!month_weekday_last{month{0}, sun[last]}.ok(), "");
+    static_assert(mwdl1.month() == feb, "");
+    static_assert(mwdl1.weekday_last() == sat[last], "");
+    static_assert(mwdl2.month() == mar, "");
+    static_assert(mwdl2.weekday_last() == mon[last], "");
+    static_assert(mwdl1 == mwdl1, "");
+    static_assert(mwdl1 != mwdl2, "");
+    std::ostringstream os;
+    os << mwdl1;
+    assert(os.str() == "Feb/Sat[last]");
+}
diff --git a/third_party/date-3.0.1/test/date_test/month_weekday_last_less.fail.cpp b/third_party/date-3.0.1/test/date_test/month_weekday_last_less.fail.cpp
new file mode 100644
index 00000000..beee0e14
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/month_weekday_last_less.fail.cpp
@@ -0,0 +1,34 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// month_weekday_last < month_weekday_last not allowed
+
+#include "date.h"
+
+int
+main()
+{
+    using namespace date;
+    month_weekday_last mwdl1 = {feb, sat[last]};
+    month_weekday_last mwdl2 = {mar, mon[last]};
+    auto b = mwdl1 < mwdl2;
+}
diff --git a/third_party/date-3.0.1/test/date_test/month_weekday_less.fail.cpp b/third_party/date-3.0.1/test/date_test/month_weekday_less.fail.cpp
new file mode 100644
index 00000000..b3ead830
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/month_weekday_less.fail.cpp
@@ -0,0 +1,34 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// month_weekday < month_weekday not allowed
+
+#include "date.h"
+
+int
+main()
+{
+    using namespace date;
+    month_weekday mwd1 = {feb, sat[4]};
+    month_weekday mwd2 = {mar, mon[1]};
+    auto b = mwd1 < mwd2;
+}
diff --git a/third_party/date-3.0.1/test/date_test/monthpmonth.fail.cpp b/third_party/date-3.0.1/test/date_test/monthpmonth.fail.cpp
new file mode 100644
index 00000000..0f73aae3
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/monthpmonth.fail.cpp
@@ -0,0 +1,32 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// month + month not allowed
+
+#include "date.h"
+
+int
+main()
+{
+    using namespace date;
+    auto x = mar + jul;
+}
diff --git a/third_party/date-3.0.1/test/date_test/months_m_year_month.fail.cpp b/third_party/date-3.0.1/test/date_test/months_m_year_month.fail.cpp
new file mode 100644
index 00000000..74ada086
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/months_m_year_month.fail.cpp
@@ -0,0 +1,33 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// months - year_month not allowed
+
+#include "date.h"
+
+int
+main()
+{
+    using namespace date;
+
+    auto x = months{1} - year_month{2015_y, jan};
+}
diff --git a/third_party/date-3.0.1/test/date_test/months_m_year_month_day.fail.cpp b/third_party/date-3.0.1/test/date_test/months_m_year_month_day.fail.cpp
new file mode 100644
index 00000000..8d48619d
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/months_m_year_month_day.fail.cpp
@@ -0,0 +1,33 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// months - year_month_day not allowed
+
+#include "date.h"
+
+int
+main()
+{
+    using namespace date;
+
+    auto x = jan - year_month_day{2015_y, aug, 9_d};
+}
diff --git a/third_party/date-3.0.1/test/date_test/monthsmmonth.fail.cpp b/third_party/date-3.0.1/test/date_test/monthsmmonth.fail.cpp
new file mode 100644
index 00000000..e3fa50c3
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/monthsmmonth.fail.cpp
@@ -0,0 +1,32 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// months - month not allowed
+
+#include "date.h"
+
+int
+main()
+{
+    using namespace date;
+    auto x = months{3} - jul;
+}
diff --git a/third_party/date-3.0.1/test/date_test/multi_year_duration_addition.pass.cpp b/third_party/date-3.0.1/test/date_test/multi_year_duration_addition.pass.cpp
new file mode 100644
index 00000000..5d1d0310
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/multi_year_duration_addition.pass.cpp
@@ -0,0 +1,487 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2018 Tomasz Kamiński
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+#include "date.h"
+#include <chrono>
+#include <cassert>
+#include <type_traits>
+
+#define CPP11_ASSERT(...) static_assert(__VA_ARGS__, "")
+
+#if __cplusplus >= 201402
+// C++14
+#  define CPP14_ASSERT(...) static_assert(__VA_ARGS__, "")
+#else
+// C++11
+#  define CPP14_ASSERT(...) assert(__VA_ARGS__)
+#endif
+
+#define NOEXCEPT_ASSERT(...) static_assert(noexcept(__VA_ARGS__), "")
+
+//Invocation involves a conversion between duration that is currently
+//not marked as noexcept.
+#define NOEXCEPT_CONVERSION(...)
+
+template<typename T>
+constexpr T copy(T const& t) noexcept { return t; }
+
+struct ConvertibleToYears
+{
+   CONSTCD11 operator date::years() const NOEXCEPT
+   { return date::years{1}; };
+};
+
+struct ConvertibleToMonths
+{
+   CONSTCD11 operator date::months() const NOEXCEPT
+   { return date::months{1}; };
+};
+
+struct ConvertibleToYearsAndMonths
+{
+   CONSTCD11 operator date::years() const NOEXCEPT
+   { return date::years{1}; };
+
+   CONSTCD11 operator date::months() const NOEXCEPT
+   { return date::months{1}; };
+
+};
+
+int
+main()
+{
+    using namespace date;
+    using namespace std::chrono;
+
+    using decades = duration<int, date::detail::ratio_multiply<std::ratio<10>, years::period>>;
+    using decamonths = duration<int, date::detail::ratio_multiply<std::ratio<10>, months::period>>;
+
+    constexpr months one_month{1};
+    constexpr years one_year{1};
+    constexpr decades one_decade{1};
+    constexpr decamonths one_decamonth{1};
+
+    constexpr ConvertibleToMonths custom_month;
+    constexpr ConvertibleToYears custom_year;
+    constexpr ConvertibleToYearsAndMonths prefer_year;
+    
+
+    {
+       constexpr year_month ym = 2001_y/feb;
+       CPP14_ASSERT(ym + one_month == 2001_y/mar);
+       NOEXCEPT_ASSERT(ym + one_month);
+       CPP14_ASSERT(one_month + ym == 2001_y/mar);
+       NOEXCEPT_ASSERT(one_month + ym);
+       CPP14_ASSERT(ym - one_month == 2001_y/jan);
+       NOEXCEPT_ASSERT(ym - one_month);
+       CPP14_ASSERT((copy(ym) += one_month) == 2001_y/mar);
+       NOEXCEPT_ASSERT(copy(ym) += one_month);
+       CPP14_ASSERT((copy(ym) -= one_month) == 2001_y/jan);
+       NOEXCEPT_ASSERT(copy(ym) -= one_month);
+      
+       CPP11_ASSERT(ym + one_year == 2002_y/feb);
+       NOEXCEPT_ASSERT(ym + one_year);
+       CPP11_ASSERT(one_year + ym == 2002_y/feb);
+       NOEXCEPT_ASSERT(one_year + ym);
+       CPP11_ASSERT(ym - one_year == 2000_y/feb);
+       NOEXCEPT_ASSERT(ym - one_year);
+       CPP14_ASSERT((copy(ym) += one_year) == 2002_y/feb);
+       NOEXCEPT_ASSERT(copy(ym) += one_year);
+       CPP14_ASSERT((copy(ym) -= one_year) == 2000_y/feb);
+       NOEXCEPT_ASSERT(copy(ym) -= one_year);
+
+       CPP11_ASSERT(ym + one_decade == 2011_y/feb);
+       NOEXCEPT_CONVERSION(ym + one_decade);
+       CPP11_ASSERT(one_decade + ym == 2011_y/feb);
+       NOEXCEPT_CONVERSION(one_decade + ym);
+       CPP11_ASSERT(ym - one_decade == 1991_y/feb);
+       NOEXCEPT_CONVERSION(ym - one_decade);
+       CPP14_ASSERT((copy(ym) += one_decade) == 2011_y/feb);
+       NOEXCEPT_CONVERSION(copy(ym) += one_decade);
+       CPP14_ASSERT((copy(ym) -= one_decade) == 1991_y/feb);
+       NOEXCEPT_CONVERSION(copy(ym) -= one_decade);
+
+       CPP14_ASSERT(ym + one_decamonth == 2001_y/dec);
+       NOEXCEPT_CONVERSION(ym + one_decamonth);
+       CPP14_ASSERT(one_decamonth + ym  == 2001_y/dec);
+       NOEXCEPT_CONVERSION(one_decamonth + ym);
+       CPP14_ASSERT(ym - one_decamonth == 2000_y/apr);
+       NOEXCEPT_CONVERSION(ym - one_decamonth);
+       CPP14_ASSERT((copy(ym) += one_decamonth) == 2001_y/dec);
+       NOEXCEPT_CONVERSION(copy(ym) += one_decamonth);
+       CPP14_ASSERT((copy(ym) -= one_decamonth) == 2000_y/apr);
+       NOEXCEPT_CONVERSION(copy(ym) -= one_decamonth);
+
+       CPP14_ASSERT(ym + custom_month == 2001_y/mar);
+       NOEXCEPT_ASSERT(ym + custom_month);
+       CPP14_ASSERT(custom_month + ym == 2001_y/mar);
+       NOEXCEPT_ASSERT(custom_month + ym);
+       CPP14_ASSERT(ym - custom_month == 2001_y/jan);
+       NOEXCEPT_ASSERT(ym - custom_month);
+       CPP14_ASSERT((copy(ym) += custom_month) == 2001_y/mar);
+       NOEXCEPT_ASSERT(copy(ym) += custom_month);
+       CPP14_ASSERT((copy(ym) -= custom_month) == 2001_y/jan);
+       NOEXCEPT_ASSERT(copy(ym) -= custom_month);
+      
+       CPP11_ASSERT(ym + custom_year == 2002_y/feb);
+       NOEXCEPT_ASSERT(ym + custom_year);
+       CPP11_ASSERT(custom_year + ym == 2002_y/feb);
+       NOEXCEPT_ASSERT(custom_year + ym);
+       CPP11_ASSERT(ym - custom_year == 2000_y/feb);
+       NOEXCEPT_ASSERT(ym - custom_year);
+       CPP14_ASSERT((copy(ym) += custom_year) == 2002_y/feb);
+       NOEXCEPT_ASSERT(copy(ym) += custom_year);
+       CPP14_ASSERT((copy(ym) -= custom_year) == 2000_y/feb);
+       NOEXCEPT_ASSERT(copy(ym) -= custom_year);
+
+       CPP11_ASSERT(ym + prefer_year == 2002_y/feb);
+       NOEXCEPT_ASSERT(ym + prefer_year);
+       CPP11_ASSERT(prefer_year + ym == 2002_y/feb);
+       NOEXCEPT_ASSERT(prefer_year + ym);
+       CPP11_ASSERT(ym - prefer_year == 2000_y/feb);
+       NOEXCEPT_ASSERT(ym - prefer_year);
+       CPP14_ASSERT((copy(ym) += prefer_year) == 2002_y/feb);
+       NOEXCEPT_ASSERT(copy(ym) += prefer_year);
+       CPP14_ASSERT((copy(ym) -= prefer_year) == 2000_y/feb);
+       NOEXCEPT_ASSERT(copy(ym) -= prefer_year);
+    }
+
+    {
+       constexpr year_month_day ym = 2001_y/feb/10;
+       CPP14_ASSERT(ym + one_month == 2001_y/mar/10);
+       NOEXCEPT_ASSERT(ym + one_month);
+       CPP14_ASSERT(one_month + ym == 2001_y/mar/10);
+       NOEXCEPT_ASSERT(one_month + ym);
+       CPP14_ASSERT(ym - one_month == 2001_y/jan/10);
+       NOEXCEPT_ASSERT(ym - one_month);
+       CPP14_ASSERT((copy(ym) += one_month) == 2001_y/mar/10);
+       NOEXCEPT_ASSERT(copy(ym) += one_month);
+       CPP14_ASSERT((copy(ym) -= one_month) == 2001_y/jan/10);
+       NOEXCEPT_ASSERT(copy(ym) -= one_month);
+      
+       CPP11_ASSERT(ym + one_year == 2002_y/feb/10);
+       NOEXCEPT_ASSERT(ym + one_year);
+       CPP11_ASSERT(one_year + ym == 2002_y/feb/10);
+       NOEXCEPT_ASSERT(one_year + ym);
+       CPP11_ASSERT(ym - one_year == 2000_y/feb/10);
+       NOEXCEPT_ASSERT(ym - one_year);
+       CPP14_ASSERT((copy(ym) += one_year) == 2002_y/feb/10);
+       NOEXCEPT_ASSERT(copy(ym) += one_year);
+       CPP14_ASSERT((copy(ym) -= one_year) == 2000_y/feb/10);
+       NOEXCEPT_ASSERT(copy(ym) -= one_year);
+
+       CPP11_ASSERT(ym + one_decade == 2011_y/feb/10);
+       NOEXCEPT_CONVERSION(ym + one_decade);
+       CPP11_ASSERT(one_decade + ym == 2011_y/feb/10);
+       NOEXCEPT_CONVERSION(one_decade + ym);
+       CPP11_ASSERT(ym - one_decade == 1991_y/feb/10);
+       NOEXCEPT_CONVERSION(ym - one_decade);
+       CPP14_ASSERT((copy(ym) += one_decade) == 2011_y/feb/10);
+       NOEXCEPT_CONVERSION(copy(ym) += one_decade);
+       CPP14_ASSERT((copy(ym) -= one_decade) == 1991_y/feb/10);
+       NOEXCEPT_CONVERSION(copy(ym) -= one_decade);
+
+       CPP14_ASSERT(ym + one_decamonth == 2001_y/dec/10);
+       NOEXCEPT_CONVERSION(ym + one_decamonth);
+       CPP14_ASSERT(one_decamonth + ym  == 2001_y/dec/10);
+       NOEXCEPT_CONVERSION(one_decamonth + ym);
+       CPP14_ASSERT(ym - one_decamonth == 2000_y/apr/10);
+       NOEXCEPT_CONVERSION(ym - one_decamonth);
+       CPP14_ASSERT((copy(ym) += one_decamonth) == 2001_y/dec/10);
+       NOEXCEPT_CONVERSION(copy(ym) += one_decamonth);
+       CPP14_ASSERT((copy(ym) -= one_decamonth) == 2000_y/apr/10);
+       NOEXCEPT_CONVERSION(copy(ym) -= one_decamonth);
+
+       CPP14_ASSERT(ym + custom_month == 2001_y/mar/10);
+       NOEXCEPT_ASSERT(ym + custom_month);
+       CPP14_ASSERT(custom_month + ym == 2001_y/mar/10);
+       NOEXCEPT_ASSERT(custom_month + ym);
+       CPP14_ASSERT(ym - custom_month == 2001_y/jan/10);
+       NOEXCEPT_ASSERT(ym - custom_month);
+       CPP14_ASSERT((copy(ym) += custom_month) == 2001_y/mar/10);
+       NOEXCEPT_ASSERT(copy(ym) += custom_month);
+       CPP14_ASSERT((copy(ym) -= custom_month) == 2001_y/jan/10);
+       NOEXCEPT_ASSERT(copy(ym) -= custom_month);
+      
+       CPP11_ASSERT(ym + custom_year == 2002_y/feb/10);
+       NOEXCEPT_ASSERT(ym + custom_year);
+       CPP11_ASSERT(custom_year + ym == 2002_y/feb/10);
+       NOEXCEPT_ASSERT(custom_year + ym);
+       CPP11_ASSERT(ym - custom_year == 2000_y/feb/10);
+       NOEXCEPT_ASSERT(ym - custom_year);
+       CPP14_ASSERT((copy(ym) += custom_year) == 2002_y/feb/10);
+       NOEXCEPT_ASSERT(copy(ym) += custom_year);
+       CPP14_ASSERT((copy(ym) -= custom_year) == 2000_y/feb/10);
+       NOEXCEPT_ASSERT(copy(ym) -= custom_year);
+
+       CPP11_ASSERT(ym + prefer_year == 2002_y/feb/10);
+       NOEXCEPT_ASSERT(ym + prefer_year);
+       CPP11_ASSERT(prefer_year + ym == 2002_y/feb/10);
+       NOEXCEPT_ASSERT(prefer_year + ym);
+       CPP11_ASSERT(ym - prefer_year == 2000_y/feb/10);
+       NOEXCEPT_ASSERT(ym - prefer_year);
+       CPP14_ASSERT((copy(ym) += prefer_year) == 2002_y/feb/10);
+       NOEXCEPT_ASSERT(copy(ym) += prefer_year);
+       CPP14_ASSERT((copy(ym) -= prefer_year) == 2000_y/feb/10);
+       NOEXCEPT_ASSERT(copy(ym) -= prefer_year);
+    }
+
+    {
+       constexpr year_month_day_last ym = 2001_y/feb/last;
+       CPP14_ASSERT(ym + one_month == 2001_y/mar/last);
+       NOEXCEPT_ASSERT(ym + one_month);
+       CPP14_ASSERT(one_month + ym == 2001_y/mar/last);
+       NOEXCEPT_ASSERT(one_month + ym);
+       CPP14_ASSERT(ym - one_month == 2001_y/jan/last);
+       NOEXCEPT_ASSERT(ym - one_month);
+       CPP14_ASSERT((copy(ym) += one_month) == 2001_y/mar/last);
+       NOEXCEPT_ASSERT(copy(ym) += one_month);
+       CPP14_ASSERT((copy(ym) -= one_month) == 2001_y/jan/last);
+       NOEXCEPT_ASSERT(copy(ym) -= one_month);
+      
+       CPP11_ASSERT(ym + one_year == 2002_y/feb/last);
+       NOEXCEPT_ASSERT(ym + one_year);
+       CPP11_ASSERT(one_year + ym == 2002_y/feb/last);
+       NOEXCEPT_ASSERT(one_year + ym);
+       CPP11_ASSERT(ym - one_year == 2000_y/feb/last);
+       NOEXCEPT_ASSERT(ym - one_year);
+       CPP14_ASSERT((copy(ym) += one_year) == 2002_y/feb/last);
+       NOEXCEPT_ASSERT(copy(ym) += one_year);
+       CPP14_ASSERT((copy(ym) -= one_year) == 2000_y/feb/last);
+       NOEXCEPT_ASSERT(copy(ym) -= one_year);
+
+       CPP11_ASSERT(ym + one_decade == 2011_y/feb/last);
+       NOEXCEPT_CONVERSION(ym + one_decade);
+       CPP11_ASSERT(one_decade + ym == 2011_y/feb/last);
+       NOEXCEPT_CONVERSION(one_decade + ym);
+       CPP11_ASSERT(ym - one_decade == 1991_y/feb/last);
+       NOEXCEPT_CONVERSION(ym - one_decade);
+       CPP14_ASSERT((copy(ym) += one_decade) == 2011_y/feb/last);
+       NOEXCEPT_CONVERSION(copy(ym) += one_decade);
+       CPP14_ASSERT((copy(ym) -= one_decade) == 1991_y/feb/last);
+       NOEXCEPT_CONVERSION(copy(ym) -= one_decade);
+
+       CPP14_ASSERT(ym + one_decamonth == 2001_y/dec/last);
+       NOEXCEPT_CONVERSION(ym + one_decamonth);
+       CPP14_ASSERT(one_decamonth + ym  == 2001_y/dec/last);
+       NOEXCEPT_CONVERSION(one_decamonth + ym);
+       CPP14_ASSERT(ym - one_decamonth == 2000_y/apr/last);
+       NOEXCEPT_CONVERSION(ym - one_decamonth);
+       CPP14_ASSERT((copy(ym) += one_decamonth) == 2001_y/dec/last);
+       NOEXCEPT_CONVERSION(copy(ym) += one_decamonth);
+       CPP14_ASSERT((copy(ym) -= one_decamonth) == 2000_y/apr/last);
+       NOEXCEPT_CONVERSION(copy(ym) -= one_decamonth);
+
+       CPP14_ASSERT(ym + custom_month == 2001_y/mar/last);
+       NOEXCEPT_ASSERT(ym + custom_month);
+       CPP14_ASSERT(custom_month + ym == 2001_y/mar/last);
+       NOEXCEPT_ASSERT(custom_month + ym);
+       CPP14_ASSERT(ym - custom_month == 2001_y/jan/last);
+       NOEXCEPT_ASSERT(ym - custom_month);
+       CPP14_ASSERT((copy(ym) += custom_month) == 2001_y/mar/last);
+       NOEXCEPT_ASSERT(copy(ym) += custom_month);
+       CPP14_ASSERT((copy(ym) -= custom_month) == 2001_y/jan/last);
+       NOEXCEPT_ASSERT(copy(ym) -= custom_month);
+      
+       CPP11_ASSERT(ym + custom_year == 2002_y/feb/last);
+       NOEXCEPT_ASSERT(ym + custom_year);
+       CPP11_ASSERT(custom_year + ym == 2002_y/feb/last);
+       NOEXCEPT_ASSERT(custom_year + ym);
+       CPP11_ASSERT(ym - custom_year == 2000_y/feb/last);
+       NOEXCEPT_ASSERT(ym - custom_year);
+       CPP14_ASSERT((copy(ym) += custom_year) == 2002_y/feb/last);
+       NOEXCEPT_ASSERT(copy(ym) += custom_year);
+       CPP14_ASSERT((copy(ym) -= custom_year) == 2000_y/feb/last);
+       NOEXCEPT_ASSERT(copy(ym) -= custom_year);
+
+       CPP11_ASSERT(ym + prefer_year == 2002_y/feb/last);
+       NOEXCEPT_ASSERT(ym + prefer_year);
+       CPP11_ASSERT(prefer_year + ym == 2002_y/feb/last);
+       NOEXCEPT_ASSERT(prefer_year + ym);
+       CPP11_ASSERT(ym - prefer_year == 2000_y/feb/last);
+       NOEXCEPT_ASSERT(ym - prefer_year);
+       CPP14_ASSERT((copy(ym) += prefer_year) == 2002_y/feb/last);
+       NOEXCEPT_ASSERT(copy(ym) += prefer_year);
+       CPP14_ASSERT((copy(ym) -= prefer_year) == 2000_y/feb/last);
+       NOEXCEPT_ASSERT(copy(ym) -= prefer_year);
+    }
+
+    {
+       constexpr year_month_weekday ym = 2001_y/feb/fri[4];
+       CPP14_ASSERT(ym + one_month == 2001_y/mar/fri[4]);
+       NOEXCEPT_ASSERT(ym + one_month);
+       CPP14_ASSERT(one_month + ym == 2001_y/mar/fri[4]);
+       NOEXCEPT_ASSERT(one_month + ym);
+       CPP14_ASSERT(ym - one_month == 2001_y/jan/fri[4]);
+       NOEXCEPT_ASSERT(ym - one_month);
+       CPP14_ASSERT((copy(ym) += one_month) == 2001_y/mar/fri[4]);
+       NOEXCEPT_ASSERT(copy(ym) += one_month);
+       CPP14_ASSERT((copy(ym) -= one_month) == 2001_y/jan/fri[4]);
+       NOEXCEPT_ASSERT(copy(ym) -= one_month);
+      
+       CPP11_ASSERT(ym + one_year == 2002_y/feb/fri[4]);
+       NOEXCEPT_ASSERT(ym + one_year);
+       CPP11_ASSERT(one_year + ym == 2002_y/feb/fri[4]);
+       NOEXCEPT_ASSERT(one_year + ym);
+       CPP11_ASSERT(ym - one_year == 2000_y/feb/fri[4]);
+       NOEXCEPT_ASSERT(ym - one_year);
+       CPP14_ASSERT((copy(ym) += one_year) == 2002_y/feb/fri[4]);
+       NOEXCEPT_ASSERT(copy(ym) += one_year);
+       CPP14_ASSERT((copy(ym) -= one_year) == 2000_y/feb/fri[4]);
+       NOEXCEPT_ASSERT(copy(ym) -= one_year);
+
+       CPP11_ASSERT(ym + one_decade == 2011_y/feb/fri[4]);
+       NOEXCEPT_CONVERSION(ym + one_decade);
+       CPP11_ASSERT(one_decade + ym == 2011_y/feb/fri[4]);
+       NOEXCEPT_CONVERSION(one_decade + ym);
+       CPP11_ASSERT(ym - one_decade == 1991_y/feb/fri[4]);
+       NOEXCEPT_CONVERSION(ym - one_decade);
+       CPP14_ASSERT((copy(ym) += one_decade) == 2011_y/feb/fri[4]);
+       NOEXCEPT_CONVERSION(copy(ym) += one_decade);
+       CPP14_ASSERT((copy(ym) -= one_decade) == 1991_y/feb/fri[4]);
+       NOEXCEPT_CONVERSION(copy(ym) -= one_decade);
+
+       CPP14_ASSERT(ym + one_decamonth == 2001_y/dec/fri[4]);
+       NOEXCEPT_CONVERSION(ym + one_decamonth);
+       CPP14_ASSERT(one_decamonth + ym  == 2001_y/dec/fri[4]);
+       NOEXCEPT_CONVERSION(one_decamonth + ym);
+       CPP14_ASSERT(ym - one_decamonth == 2000_y/apr/fri[4]);
+       NOEXCEPT_CONVERSION(ym - one_decamonth);
+       CPP14_ASSERT((copy(ym) += one_decamonth) == 2001_y/dec/fri[4]);
+       NOEXCEPT_CONVERSION(copy(ym) += one_decamonth);
+       CPP14_ASSERT((copy(ym) -= one_decamonth) == 2000_y/apr/fri[4]);
+       NOEXCEPT_CONVERSION(copy(ym) -= one_decamonth);
+
+       CPP14_ASSERT(ym + custom_month == 2001_y/mar/fri[4]);
+       NOEXCEPT_ASSERT(ym + custom_month);
+       CPP14_ASSERT(custom_month + ym == 2001_y/mar/fri[4]);
+       NOEXCEPT_ASSERT(custom_month + ym);
+       CPP14_ASSERT(ym - custom_month == 2001_y/jan/fri[4]);
+       NOEXCEPT_ASSERT(ym - custom_month);
+       CPP14_ASSERT((copy(ym) += custom_month) == 2001_y/mar/fri[4]);
+       NOEXCEPT_ASSERT(copy(ym) += custom_month);
+       CPP14_ASSERT((copy(ym) -= custom_month) == 2001_y/jan/fri[4]);
+       NOEXCEPT_ASSERT(copy(ym) -= custom_month);
+      
+       CPP11_ASSERT(ym + custom_year == 2002_y/feb/fri[4]);
+       NOEXCEPT_ASSERT(ym + custom_year);
+       CPP11_ASSERT(custom_year + ym == 2002_y/feb/fri[4]);
+       NOEXCEPT_ASSERT(custom_year + ym);
+       CPP11_ASSERT(ym - custom_year == 2000_y/feb/fri[4]);
+       NOEXCEPT_ASSERT(ym - custom_year);
+       CPP14_ASSERT((copy(ym) += custom_year) == 2002_y/feb/fri[4]);
+       NOEXCEPT_ASSERT(copy(ym) += custom_year);
+       CPP14_ASSERT((copy(ym) -= custom_year) == 2000_y/feb/fri[4]);
+       NOEXCEPT_ASSERT(copy(ym) -= custom_year);
+
+       CPP11_ASSERT(ym + prefer_year == 2002_y/feb/fri[4]);
+       NOEXCEPT_ASSERT(ym + prefer_year);
+       CPP11_ASSERT(prefer_year + ym == 2002_y/feb/fri[4]);
+       NOEXCEPT_ASSERT(prefer_year + ym);
+       CPP11_ASSERT(ym - prefer_year == 2000_y/feb/fri[4]);
+       NOEXCEPT_ASSERT(ym - prefer_year);
+       CPP14_ASSERT((copy(ym) += prefer_year) == 2002_y/feb/fri[4]);
+       NOEXCEPT_ASSERT(copy(ym) += prefer_year);
+       CPP14_ASSERT((copy(ym) -= prefer_year) == 2000_y/feb/fri[4]);
+       NOEXCEPT_ASSERT(copy(ym) -= prefer_year);
+    }
+
+    {
+       constexpr year_month_weekday_last ym = 2001_y/feb/fri[last];
+       CPP14_ASSERT(ym + one_month == 2001_y/mar/fri[last]);
+       NOEXCEPT_ASSERT(ym + one_month);
+       CPP14_ASSERT(one_month + ym == 2001_y/mar/fri[last]);
+       NOEXCEPT_ASSERT(one_month + ym);
+       CPP14_ASSERT(ym - one_month == 2001_y/jan/fri[last]);
+       NOEXCEPT_ASSERT(ym - one_month);
+       CPP14_ASSERT((copy(ym) += one_month) == 2001_y/mar/fri[last]);
+       NOEXCEPT_ASSERT(copy(ym) += one_month);
+       CPP14_ASSERT((copy(ym) -= one_month) == 2001_y/jan/fri[last]);
+       NOEXCEPT_ASSERT(copy(ym) -= one_month);
+      
+       CPP11_ASSERT(ym + one_year == 2002_y/feb/fri[last]);
+       NOEXCEPT_ASSERT(ym + one_year);
+       CPP11_ASSERT(one_year + ym == 2002_y/feb/fri[last]);
+       NOEXCEPT_ASSERT(one_year + ym);
+       CPP11_ASSERT(ym - one_year == 2000_y/feb/fri[last]);
+       NOEXCEPT_ASSERT(ym - one_year);
+       CPP14_ASSERT((copy(ym) += one_year) == 2002_y/feb/fri[last]);
+       NOEXCEPT_ASSERT(copy(ym) += one_year);
+       CPP14_ASSERT((copy(ym) -= one_year) == 2000_y/feb/fri[last]);
+       NOEXCEPT_ASSERT(copy(ym) -= one_year);
+
+       CPP11_ASSERT(ym + one_decade == 2011_y/feb/fri[last]);
+       NOEXCEPT_CONVERSION(ym + one_decade);
+       CPP11_ASSERT(one_decade + ym == 2011_y/feb/fri[last]);
+       NOEXCEPT_CONVERSION(one_decade + ym);
+       CPP11_ASSERT(ym - one_decade == 1991_y/feb/fri[last]);
+       NOEXCEPT_CONVERSION(ym - one_decade);
+       CPP14_ASSERT((copy(ym) += one_decade) == 2011_y/feb/fri[last]);
+       NOEXCEPT_CONVERSION(copy(ym) += one_decade);
+       CPP14_ASSERT((copy(ym) -= one_decade) == 1991_y/feb/fri[last]);
+       NOEXCEPT_CONVERSION(copy(ym) -= one_decade);
+
+       CPP14_ASSERT(ym + one_decamonth == 2001_y/dec/fri[last]);
+       NOEXCEPT_CONVERSION(ym + one_decamonth);
+       CPP14_ASSERT(one_decamonth + ym  == 2001_y/dec/fri[last]);
+       NOEXCEPT_CONVERSION(one_decamonth + ym);
+       CPP14_ASSERT(ym - one_decamonth == 2000_y/apr/fri[last]);
+       NOEXCEPT_CONVERSION(ym - one_decamonth);
+       CPP14_ASSERT((copy(ym) += one_decamonth) == 2001_y/dec/fri[last]);
+       NOEXCEPT_CONVERSION(copy(ym) += one_decamonth);
+       CPP14_ASSERT((copy(ym) -= one_decamonth) == 2000_y/apr/fri[last]);
+       NOEXCEPT_CONVERSION(copy(ym) -= one_decamonth);
+
+       CPP14_ASSERT(ym + custom_month == 2001_y/mar/fri[last]);
+       NOEXCEPT_ASSERT(ym + custom_month);
+       CPP14_ASSERT(custom_month + ym == 2001_y/mar/fri[last]);
+       NOEXCEPT_ASSERT(custom_month + ym);
+       CPP14_ASSERT(ym - custom_month == 2001_y/jan/fri[last]);
+       NOEXCEPT_ASSERT(ym - custom_month);
+       CPP14_ASSERT((copy(ym) += custom_month) == 2001_y/mar/fri[last]);
+       NOEXCEPT_ASSERT(copy(ym) += custom_month);
+       CPP14_ASSERT((copy(ym) -= custom_month) == 2001_y/jan/fri[last]);
+       NOEXCEPT_ASSERT(copy(ym) -= custom_month);
+      
+       CPP11_ASSERT(ym + custom_year == 2002_y/feb/fri[last]);
+       NOEXCEPT_ASSERT(ym + custom_year);
+       CPP11_ASSERT(custom_year + ym == 2002_y/feb/fri[last]);
+       NOEXCEPT_ASSERT(custom_year + ym);
+       CPP11_ASSERT(ym - custom_year == 2000_y/feb/fri[last]);
+       NOEXCEPT_ASSERT(ym - custom_year);
+       CPP14_ASSERT((copy(ym) += custom_year) == 2002_y/feb/fri[last]);
+       NOEXCEPT_ASSERT(copy(ym) += custom_year);
+       CPP14_ASSERT((copy(ym) -= custom_year) == 2000_y/feb/fri[last]);
+       NOEXCEPT_ASSERT(copy(ym) -= custom_year);
+
+       CPP11_ASSERT(ym + prefer_year == 2002_y/feb/fri[last]);
+       NOEXCEPT_ASSERT(ym + prefer_year);
+       CPP11_ASSERT(prefer_year + ym == 2002_y/feb/fri[last]);
+       NOEXCEPT_ASSERT(prefer_year + ym);
+       CPP11_ASSERT(ym - prefer_year == 2000_y/feb/fri[last]);
+       NOEXCEPT_ASSERT(ym - prefer_year);
+       CPP14_ASSERT((copy(ym) += prefer_year) == 2002_y/feb/fri[last]);
+       NOEXCEPT_ASSERT(copy(ym) += prefer_year);
+       CPP14_ASSERT((copy(ym) -= prefer_year) == 2000_y/feb/fri[last]);
+       NOEXCEPT_ASSERT(copy(ym) -= prefer_year);
+    }
+}
diff --git a/third_party/date-3.0.1/test/date_test/op_div_day_day.fail.cpp b/third_party/date-3.0.1/test/date_test/op_div_day_day.fail.cpp
new file mode 100644
index 00000000..891f8140
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/op_div_day_day.fail.cpp
@@ -0,0 +1,33 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// day / day not allowed
+
+#include "date.h"
+
+int
+main()
+{
+    using namespace date;
+
+    auto x = 14_d/14_d;
+}
diff --git a/third_party/date-3.0.1/test/date_test/op_div_int_month.fail.cpp b/third_party/date-3.0.1/test/date_test/op_div_int_month.fail.cpp
new file mode 100644
index 00000000..1ecb3c11
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/op_div_int_month.fail.cpp
@@ -0,0 +1,33 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// int / month not allowed
+
+#include "date.h"
+
+int
+main()
+{
+    using namespace date;
+
+    auto x = 8/aug;
+}
diff --git a/third_party/date-3.0.1/test/date_test/op_div_int_year.fail.cpp b/third_party/date-3.0.1/test/date_test/op_div_int_year.fail.cpp
new file mode 100644
index 00000000..74a31b7d
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/op_div_int_year.fail.cpp
@@ -0,0 +1,33 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// int / year not allowed
+
+#include "date.h"
+
+int
+main()
+{
+    using namespace date;
+
+    auto x = 8/2015_y;
+}
diff --git a/third_party/date-3.0.1/test/date_test/op_div_last_last.fail.cpp b/third_party/date-3.0.1/test/date_test/op_div_last_last.fail.cpp
new file mode 100644
index 00000000..2dca2212
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/op_div_last_last.fail.cpp
@@ -0,0 +1,33 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// last / last not allowed
+
+#include "date.h"
+
+int
+main()
+{
+    using namespace date;
+
+    auto x = last/last;
+}
diff --git a/third_party/date-3.0.1/test/date_test/op_div_month_day.pass.cpp b/third_party/date-3.0.1/test/date_test/op_div_month_day.pass.cpp
new file mode 100644
index 00000000..46062f4b
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/op_div_month_day.pass.cpp
@@ -0,0 +1,41 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// constexpr month_day operator/(const month& m, const day& d) noexcept;
+// constexpr month_day operator/(const month& m, int d) noexcept;
+// constexpr month_day operator/(int   m, const day& d) noexcept;
+// constexpr month_day operator/(const day& d, const month& m) noexcept;
+// constexpr month_day operator/(const day& d,   int m) noexcept;
+
+#include "date.h"
+
+int
+main()
+{
+    using namespace date;
+
+    static_assert( aug/14_d == month_day{month{8}, day{14}}, "");
+    static_assert( aug/14   == month_day{month{8}, day{14}}, "");
+    static_assert(   8/14_d == month_day{month{8}, day{14}}, "");
+    static_assert(14_d/aug  == month_day{month{8}, day{14}}, "");
+    static_assert(14_d/8    == month_day{month{8}, day{14}}, "");
+}
diff --git a/third_party/date-3.0.1/test/date_test/op_div_month_day_last.pass.cpp b/third_party/date-3.0.1/test/date_test/op_div_month_day_last.pass.cpp
new file mode 100644
index 00000000..9de4538e
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/op_div_month_day_last.pass.cpp
@@ -0,0 +1,39 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// constexpr month_day_last operator/(const month& m, last_spec) noexcept;
+// constexpr month_day_last operator/(int   m, last_spec) noexcept;
+// constexpr month_day_last operator/(last_spec, const month& m) noexcept;
+// constexpr month_day_last operator/(last_spec, int   m) noexcept;
+
+#include "date.h"
+
+int
+main()
+{
+    using namespace date;
+
+    static_assert( aug/last == month_day_last{month{8}}, "");
+    static_assert(   8/last == month_day_last{month{8}}, "");
+    static_assert(last/aug  == month_day_last{month{8}}, "");
+    static_assert(last/8    == month_day_last{month{8}}, "");
+}
diff --git a/third_party/date-3.0.1/test/date_test/op_div_month_day_month_day.fail.cpp b/third_party/date-3.0.1/test/date_test/op_div_month_day_month_day.fail.cpp
new file mode 100644
index 00000000..20fcf0f3
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/op_div_month_day_month_day.fail.cpp
@@ -0,0 +1,33 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// month_day / month_day not allowed
+
+#include "date.h"
+
+int
+main()
+{
+    using namespace date;
+
+    auto x = (aug/14_d)/(aug/14_d);
+}
diff --git a/third_party/date-3.0.1/test/date_test/op_div_month_month.fail.cpp b/third_party/date-3.0.1/test/date_test/op_div_month_month.fail.cpp
new file mode 100644
index 00000000..85965a75
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/op_div_month_month.fail.cpp
@@ -0,0 +1,33 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// month / month not allowed
+
+#include "date.h"
+
+int
+main()
+{
+    using namespace date;
+
+    auto x = aug/aug;
+}
diff --git a/third_party/date-3.0.1/test/date_test/op_div_month_weekday.pass.cpp b/third_party/date-3.0.1/test/date_test/op_div_month_weekday.pass.cpp
new file mode 100644
index 00000000..a2311fe4
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/op_div_month_weekday.pass.cpp
@@ -0,0 +1,39 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// constexpr month_weekday operator/(const month& m, const weekday_indexed& wdi) noexcept;
+// constexpr month_weekday operator/(int   m, const weekday_indexed& wdi) noexcept;
+// constexpr month_weekday operator/(const weekday_indexed& wdi, const month& m) noexcept;
+// constexpr month_weekday operator/(const weekday_indexed& wdi, int   m) noexcept;
+
+#include "date.h"
+
+int
+main()
+{
+    using namespace date;
+
+    static_assert(   aug/fri[2] == month_weekday{month{8}, weekday_indexed{weekday{5u}, 2}}, "");
+    static_assert(     8/fri[2] == month_weekday{month{8}, weekday_indexed{weekday{5u}, 2}}, "");
+    static_assert(fri[2]/aug    == month_weekday{month{8}, weekday_indexed{weekday{5u}, 2}}, "");
+    static_assert(fri[2]/8      == month_weekday{month{8}, weekday_indexed{weekday{5u}, 2}}, "");
+}
diff --git a/third_party/date-3.0.1/test/date_test/op_div_month_weekday_last.pass.cpp b/third_party/date-3.0.1/test/date_test/op_div_month_weekday_last.pass.cpp
new file mode 100644
index 00000000..0024960d
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/op_div_month_weekday_last.pass.cpp
@@ -0,0 +1,39 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// constexpr month_weekday_last operator/(const month& m, const weekday_last& wdl) noexcept;
+// constexpr month_weekday_last operator/(int   m, const weekday_last& wdl) noexcept;
+// constexpr month_weekday_last operator/(const weekday_last& wdl, const month& m) noexcept;
+// constexpr month_weekday_last operator/(const weekday_last& wdl, int   m) noexcept;
+
+#include "date.h"
+
+int
+main()
+{
+    using namespace date;
+
+    static_assert(      aug/fri[last] == month_weekday_last{month{8}, weekday_last{weekday{5u}}}, "");
+    static_assert(        8/fri[last] == month_weekday_last{month{8}, weekday_last{weekday{5u}}}, "");
+    static_assert(fri[last]/aug       == month_weekday_last{month{8}, weekday_last{weekday{5u}}}, "");
+    static_assert(fri[last]/8         == month_weekday_last{month{8}, weekday_last{weekday{5u}}}, "");
+}
diff --git a/third_party/date-3.0.1/test/date_test/op_div_month_year.fail.cpp b/third_party/date-3.0.1/test/date_test/op_div_month_year.fail.cpp
new file mode 100644
index 00000000..c3af87f2
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/op_div_month_year.fail.cpp
@@ -0,0 +1,33 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// month / year not allowed
+
+#include "date.h"
+
+int
+main()
+{
+    using namespace date;
+
+    auto x = aug/2015_y;
+}
diff --git a/third_party/date-3.0.1/test/date_test/op_div_survey.pass.cpp b/third_party/date-3.0.1/test/date_test/op_div_survey.pass.cpp
new file mode 100644
index 00000000..987850f0
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/op_div_survey.pass.cpp
@@ -0,0 +1,437 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+#include "date.h"
+
+#include <type_traits>
+
+template <class I, class J, class K>
+constexpr
+auto
+test(I i, J j, K k) -> decltype(i/j/k)
+{
+    return i/j/k;
+}
+
+void
+test(...)
+{
+}
+
+int
+main()
+{
+    using std::is_same;
+    using namespace date;
+
+    static_assert(is_same<decltype(test(        1,         1,         1)), int>{}, "");
+    static_assert(is_same<decltype(test(        1,         1,       1_d)), month_day>{}, "");
+    static_assert(is_same<decltype(test(        1,         1,       jan)), void>{}, "");
+    static_assert(is_same<decltype(test(        1,         1,       1_y)), void>{}, "");
+    static_assert(is_same<decltype(test(        1,         1,      last)), month_day_last>{}, "");
+    static_assert(is_same<decltype(test(        1,         1,    sun[1])), month_weekday>{}, "");
+    static_assert(is_same<decltype(test(        1,         1, sun[last])), month_weekday_last>{}, "");
+
+    static_assert(is_same<decltype(test(        1,       1_d,         1)), year_month_day>{}, "");
+    static_assert(is_same<decltype(test(        1,       1_d,       1_d)), void>{}, "");
+    static_assert(is_same<decltype(test(        1,       1_d,       jan)), void>{}, "");
+    static_assert(is_same<decltype(test(        1,       1_d,       1_y)), year_month_day>{}, "");
+    static_assert(is_same<decltype(test(        1,       1_d,      last)), void>{}, "");
+    static_assert(is_same<decltype(test(        1,       1_d,    sun[1])), void>{}, "");
+    static_assert(is_same<decltype(test(        1,       1_d, sun[last])), void>{}, "");
+
+    static_assert(is_same<decltype(test(        1,       jan,         1)), void>{}, "");
+    static_assert(is_same<decltype(test(        1,       jan,       1_d)), void>{}, "");
+    static_assert(is_same<decltype(test(        1,       jan,       jan)), void>{}, "");
+    static_assert(is_same<decltype(test(        1,       jan,       1_y)), void>{}, "");
+    static_assert(is_same<decltype(test(        1,       jan,      last)), void>{}, "");
+    static_assert(is_same<decltype(test(        1,       jan,    sun[1])), void>{}, "");
+    static_assert(is_same<decltype(test(        1,       jan, sun[last])), void>{}, "");
+
+    static_assert(is_same<decltype(test(        1,       1_y,         1)), void>{}, "");
+    static_assert(is_same<decltype(test(        1,       1_y,       1_d)), void>{}, "");
+    static_assert(is_same<decltype(test(        1,       1_y,       jan)), void>{}, "");
+    static_assert(is_same<decltype(test(        1,       1_y,       1_y)), void>{}, "");
+    static_assert(is_same<decltype(test(        1,       1_y,      last)), void>{}, "");
+    static_assert(is_same<decltype(test(        1,       1_y,    sun[1])), void>{}, "");
+    static_assert(is_same<decltype(test(        1,       1_y, sun[last])), void>{}, "");
+
+    static_assert(is_same<decltype(test(        1,      last,         1)), year_month_day_last>{}, "");
+    static_assert(is_same<decltype(test(        1,      last,       1_d)), void>{}, "");
+    static_assert(is_same<decltype(test(        1,      last,       jan)), void>{}, "");
+    static_assert(is_same<decltype(test(        1,      last,       1_y)), year_month_day_last>{}, "");
+    static_assert(is_same<decltype(test(        1,      last,      last)), void>{}, "");
+    static_assert(is_same<decltype(test(        1,      last,    sun[1])), void>{}, "");
+    static_assert(is_same<decltype(test(        1,      last, sun[last])), void>{}, "");
+
+    static_assert(is_same<decltype(test(        1,    sun[1],         1)), year_month_weekday>{}, "");
+    static_assert(is_same<decltype(test(        1,    sun[1],       1_d)), void>{}, "");
+    static_assert(is_same<decltype(test(        1,    sun[1],       jan)), void>{}, "");
+    static_assert(is_same<decltype(test(        1,    sun[1],       1_y)), year_month_weekday>{}, "");
+    static_assert(is_same<decltype(test(        1,    sun[1],      last)), void>{}, "");
+    static_assert(is_same<decltype(test(        1,    sun[1],    sun[1])), void>{}, "");
+    static_assert(is_same<decltype(test(        1,    sun[1], sun[last])), void>{}, "");
+
+    static_assert(is_same<decltype(test(        1, sun[last],         1)), year_month_weekday_last>{}, "");
+    static_assert(is_same<decltype(test(        1, sun[last],       1_d)), void>{}, "");
+    static_assert(is_same<decltype(test(        1, sun[last],       jan)), void>{}, "");
+    static_assert(is_same<decltype(test(        1, sun[last],       1_y)), year_month_weekday_last>{}, "");
+    static_assert(is_same<decltype(test(        1, sun[last],      last)), void>{}, "");
+    static_assert(is_same<decltype(test(        1, sun[last],    sun[1])), void>{}, "");
+    static_assert(is_same<decltype(test(        1, sun[last], sun[last])), void>{}, "");
+
+    static_assert(is_same<decltype(test(      1_d,         1,         1)), year_month_day>{}, "");
+    static_assert(is_same<decltype(test(      1_d,         1,       1_d)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_d,         1,       jan)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_d,         1,       1_y)), year_month_day>{}, "");
+    static_assert(is_same<decltype(test(      1_d,         1,      last)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_d,         1,    sun[1])), void>{}, "");
+    static_assert(is_same<decltype(test(      1_d,         1, sun[last])), void>{}, "");
+
+    static_assert(is_same<decltype(test(      1_d,       1_d,         1)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_d,       1_d,       1_d)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_d,       1_d,       jan)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_d,       1_d,       1_y)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_d,       1_d,      last)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_d,       1_d,    sun[1])), void>{}, "");
+    static_assert(is_same<decltype(test(      1_d,       1_d, sun[last])), void>{}, "");
+
+    static_assert(is_same<decltype(test(      1_d,       jan,         1)), year_month_day>{}, "");
+    static_assert(is_same<decltype(test(      1_d,       jan,       1_d)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_d,       jan,       jan)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_d,       jan,       1_y)), year_month_day>{}, "");
+    static_assert(is_same<decltype(test(      1_d,       jan,      last)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_d,       jan,    sun[1])), void>{}, "");
+    static_assert(is_same<decltype(test(      1_d,       jan, sun[last])), void>{}, "");
+
+    static_assert(is_same<decltype(test(      1_d,       1_y,         1)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_d,       1_y,       1_d)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_d,       1_y,       jan)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_d,       1_y,       1_y)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_d,       1_y,      last)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_d,       1_y,    sun[1])), void>{}, "");
+    static_assert(is_same<decltype(test(      1_d,       1_y, sun[last])), void>{}, "");
+
+    static_assert(is_same<decltype(test(      1_d,      last,         1)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_d,      last,       1_d)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_d,      last,       jan)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_d,      last,       1_y)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_d,      last,      last)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_d,      last,    sun[1])), void>{}, "");
+    static_assert(is_same<decltype(test(      1_d,      last, sun[last])), void>{}, "");
+
+    static_assert(is_same<decltype(test(      1_d,    sun[1],         1)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_d,    sun[1],       1_d)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_d,    sun[1],       jan)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_d,    sun[1],       1_y)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_d,    sun[1],      last)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_d,    sun[1],    sun[1])), void>{}, "");
+    static_assert(is_same<decltype(test(      1_d,    sun[1], sun[last])), void>{}, "");
+
+    static_assert(is_same<decltype(test(      1_d, sun[last],         1)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_d, sun[last],       1_d)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_d, sun[last],       jan)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_d, sun[last],       1_y)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_d, sun[last],      last)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_d, sun[last],    sun[1])), void>{}, "");
+    static_assert(is_same<decltype(test(      1_d, sun[last], sun[last])), void>{}, "");
+
+    static_assert(is_same<decltype(test(      jan,         1,         1)), year_month_day>{}, "");
+    static_assert(is_same<decltype(test(      jan,         1,       1_d)), void>{}, "");
+    static_assert(is_same<decltype(test(      jan,         1,       jan)), void>{}, "");
+    static_assert(is_same<decltype(test(      jan,         1,       1_y)), year_month_day>{}, "");
+    static_assert(is_same<decltype(test(      jan,         1,      last)), void>{}, "");
+    static_assert(is_same<decltype(test(      jan,         1,    sun[1])), void>{}, "");
+    static_assert(is_same<decltype(test(      jan,         1, sun[last])), void>{}, "");
+
+    static_assert(is_same<decltype(test(      jan,       1_d,         1)), year_month_day>{}, "");
+    static_assert(is_same<decltype(test(      jan,       1_d,       1_d)), void>{}, "");
+    static_assert(is_same<decltype(test(      jan,       1_d,       jan)), void>{}, "");
+    static_assert(is_same<decltype(test(      jan,       1_d,       1_y)), year_month_day>{}, "");
+    static_assert(is_same<decltype(test(      jan,       1_d,      last)), void>{}, "");
+    static_assert(is_same<decltype(test(      jan,       1_d,    sun[1])), void>{}, "");
+    static_assert(is_same<decltype(test(      jan,       1_d, sun[last])), void>{}, "");
+
+    static_assert(is_same<decltype(test(      jan,       jan,         1)), void>{}, "");
+    static_assert(is_same<decltype(test(      jan,       jan,       1_d)), void>{}, "");
+    static_assert(is_same<decltype(test(      jan,       jan,       jan)), void>{}, "");
+    static_assert(is_same<decltype(test(      jan,       jan,       1_y)), void>{}, "");
+    static_assert(is_same<decltype(test(      jan,       jan,      last)), void>{}, "");
+    static_assert(is_same<decltype(test(      jan,       jan,    sun[1])), void>{}, "");
+    static_assert(is_same<decltype(test(      jan,       jan, sun[last])), void>{}, "");
+
+    static_assert(is_same<decltype(test(      jan,       1_y,         1)), void>{}, "");
+    static_assert(is_same<decltype(test(      jan,       1_y,       1_d)), void>{}, "");
+    static_assert(is_same<decltype(test(      jan,       1_y,       jan)), void>{}, "");
+    static_assert(is_same<decltype(test(      jan,       1_y,       1_y)), void>{}, "");
+    static_assert(is_same<decltype(test(      jan,       1_y,      last)), void>{}, "");
+    static_assert(is_same<decltype(test(      jan,       1_y,    sun[1])), void>{}, "");
+    static_assert(is_same<decltype(test(      jan,       1_y, sun[last])), void>{}, "");
+
+    static_assert(is_same<decltype(test(      jan,      last,         1)), year_month_day_last>{}, "");
+    static_assert(is_same<decltype(test(      jan,      last,       1_d)), void>{}, "");
+    static_assert(is_same<decltype(test(      jan,      last,       jan)), void>{}, "");
+    static_assert(is_same<decltype(test(      jan,      last,       1_y)), year_month_day_last>{}, "");
+    static_assert(is_same<decltype(test(      jan,      last,      last)), void>{}, "");
+    static_assert(is_same<decltype(test(      jan,      last,    sun[1])), void>{}, "");
+    static_assert(is_same<decltype(test(      jan,      last, sun[last])), void>{}, "");
+
+    static_assert(is_same<decltype(test(      jan,    sun[1],         1)), year_month_weekday>{}, "");
+    static_assert(is_same<decltype(test(      jan,    sun[1],       1_d)), void>{}, "");
+    static_assert(is_same<decltype(test(      jan,    sun[1],       jan)), void>{}, "");
+    static_assert(is_same<decltype(test(      jan,    sun[1],       1_y)), year_month_weekday>{}, "");
+    static_assert(is_same<decltype(test(      jan,    sun[1],      last)), void>{}, "");
+    static_assert(is_same<decltype(test(      jan,    sun[1],    sun[1])), void>{}, "");
+    static_assert(is_same<decltype(test(      jan,    sun[1], sun[last])), void>{}, "");
+
+    static_assert(is_same<decltype(test(      jan, sun[last],         1)), year_month_weekday_last>{}, "");
+    static_assert(is_same<decltype(test(      jan, sun[last],       1_d)), void>{}, "");
+    static_assert(is_same<decltype(test(      jan, sun[last],       jan)), void>{}, "");
+    static_assert(is_same<decltype(test(      jan, sun[last],       1_y)), year_month_weekday_last>{}, "");
+    static_assert(is_same<decltype(test(      jan, sun[last],      last)), void>{}, "");
+    static_assert(is_same<decltype(test(      jan, sun[last],    sun[1])), void>{}, "");
+    static_assert(is_same<decltype(test(      jan, sun[last], sun[last])), void>{}, "");
+
+    static_assert(is_same<decltype(test(      1_y,         1,         1)), year_month_day>{}, "");
+    static_assert(is_same<decltype(test(      1_y,         1,       1_d)), year_month_day>{}, "");
+    static_assert(is_same<decltype(test(      1_y,         1,       jan)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_y,         1,       1_y)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_y,         1,      last)), year_month_day_last>{}, "");
+    static_assert(is_same<decltype(test(      1_y,         1,    sun[1])), year_month_weekday>{}, "");
+    static_assert(is_same<decltype(test(      1_y,         1, sun[last])), year_month_weekday_last>{}, "");
+
+    static_assert(is_same<decltype(test(      1_y,       1_d,         1)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_y,       1_d,       1_d)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_y,       1_d,       jan)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_y,       1_d,       1_y)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_y,       1_d,      last)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_y,       1_d,    sun[1])), void>{}, "");
+    static_assert(is_same<decltype(test(      1_y,       1_d, sun[last])), void>{}, "");
+
+    static_assert(is_same<decltype(test(      1_y,       jan,         1)), year_month_day>{}, "");
+    static_assert(is_same<decltype(test(      1_y,       jan,       1_d)), year_month_day>{}, "");
+    static_assert(is_same<decltype(test(      1_y,       jan,       jan)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_y,       jan,       1_y)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_y,       jan,      last)), year_month_day_last>{}, "");
+    static_assert(is_same<decltype(test(      1_y,       jan,    sun[1])), year_month_weekday>{}, "");
+    static_assert(is_same<decltype(test(      1_y,       jan, sun[last])), year_month_weekday_last>{}, "");
+
+    static_assert(is_same<decltype(test(      1_y,       1_y,         1)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_y,       1_y,       1_d)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_y,       1_y,       jan)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_y,       1_y,       1_y)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_y,       1_y,      last)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_y,       1_y,    sun[1])), void>{}, "");
+    static_assert(is_same<decltype(test(      1_y,       1_y, sun[last])), void>{}, "");
+
+    static_assert(is_same<decltype(test(      1_y,      last,         1)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_y,      last,       1_d)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_y,      last,       jan)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_y,      last,       1_y)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_y,      last,      last)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_y,      last,    sun[1])), void>{}, "");
+    static_assert(is_same<decltype(test(      1_y,      last, sun[last])), void>{}, "");
+
+    static_assert(is_same<decltype(test(      1_y,    sun[1],         1)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_y,    sun[1],       1_d)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_y,    sun[1],       jan)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_y,    sun[1],       1_y)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_y,    sun[1],      last)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_y,    sun[1],    sun[1])), void>{}, "");
+    static_assert(is_same<decltype(test(      1_y,    sun[1], sun[last])), void>{}, "");
+
+    static_assert(is_same<decltype(test(      1_y, sun[last],         1)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_y, sun[last],       1_d)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_y, sun[last],       jan)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_y, sun[last],       1_y)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_y, sun[last],      last)), void>{}, "");
+    static_assert(is_same<decltype(test(      1_y, sun[last],    sun[1])), void>{}, "");
+    static_assert(is_same<decltype(test(      1_y, sun[last], sun[last])), void>{}, "");
+
+    static_assert(is_same<decltype(test(     last,         1,         1)), year_month_day_last>{}, "");
+    static_assert(is_same<decltype(test(     last,         1,       1_d)), void>{}, "");
+    static_assert(is_same<decltype(test(     last,         1,       jan)), void>{}, "");
+    static_assert(is_same<decltype(test(     last,         1,       1_y)), year_month_day_last>{}, "");
+    static_assert(is_same<decltype(test(     last,         1,      last)), void>{}, "");
+    static_assert(is_same<decltype(test(     last,         1,    sun[1])), void>{}, "");
+    static_assert(is_same<decltype(test(     last,         1, sun[last])), void>{}, "");
+
+    static_assert(is_same<decltype(test(     last,       1_d,         1)), void>{}, "");
+    static_assert(is_same<decltype(test(     last,       1_d,       1_d)), void>{}, "");
+    static_assert(is_same<decltype(test(     last,       1_d,       jan)), void>{}, "");
+    static_assert(is_same<decltype(test(     last,       1_d,       1_y)), void>{}, "");
+    static_assert(is_same<decltype(test(     last,       1_d,      last)), void>{}, "");
+    static_assert(is_same<decltype(test(     last,       1_d,    sun[1])), void>{}, "");
+    static_assert(is_same<decltype(test(     last,       1_d, sun[last])), void>{}, "");
+
+    static_assert(is_same<decltype(test(     last,       jan,         1)), year_month_day_last>{}, "");
+    static_assert(is_same<decltype(test(     last,       jan,       1_d)), void>{}, "");
+    static_assert(is_same<decltype(test(     last,       jan,       jan)), void>{}, "");
+    static_assert(is_same<decltype(test(     last,       jan,       1_y)), year_month_day_last>{}, "");
+    static_assert(is_same<decltype(test(     last,       jan,      last)), void>{}, "");
+    static_assert(is_same<decltype(test(     last,       jan,    sun[1])), void>{}, "");
+    static_assert(is_same<decltype(test(     last,       jan, sun[last])), void>{}, "");
+
+    static_assert(is_same<decltype(test(     last,       1_y,         1)), void>{}, "");
+    static_assert(is_same<decltype(test(     last,       1_y,       1_d)), void>{}, "");
+    static_assert(is_same<decltype(test(     last,       1_y,       jan)), void>{}, "");
+    static_assert(is_same<decltype(test(     last,       1_y,       1_y)), void>{}, "");
+    static_assert(is_same<decltype(test(     last,       1_y,      last)), void>{}, "");
+    static_assert(is_same<decltype(test(     last,       1_y,    sun[1])), void>{}, "");
+    static_assert(is_same<decltype(test(     last,       1_y, sun[last])), void>{}, "");
+
+    static_assert(is_same<decltype(test(     last,      last,         1)), void>{}, "");
+    static_assert(is_same<decltype(test(     last,      last,       1_d)), void>{}, "");
+    static_assert(is_same<decltype(test(     last,      last,       jan)), void>{}, "");
+    static_assert(is_same<decltype(test(     last,      last,       1_y)), void>{}, "");
+    static_assert(is_same<decltype(test(     last,      last,      last)), void>{}, "");
+    static_assert(is_same<decltype(test(     last,      last,    sun[1])), void>{}, "");
+    static_assert(is_same<decltype(test(     last,      last, sun[last])), void>{}, "");
+
+    static_assert(is_same<decltype(test(     last,    sun[1],         1)), void>{}, "");
+    static_assert(is_same<decltype(test(     last,    sun[1],       1_d)), void>{}, "");
+    static_assert(is_same<decltype(test(     last,    sun[1],       jan)), void>{}, "");
+    static_assert(is_same<decltype(test(     last,    sun[1],       1_y)), void>{}, "");
+    static_assert(is_same<decltype(test(     last,    sun[1],      last)), void>{}, "");
+    static_assert(is_same<decltype(test(     last,    sun[1],    sun[1])), void>{}, "");
+    static_assert(is_same<decltype(test(     last,    sun[1], sun[last])), void>{}, "");
+
+    static_assert(is_same<decltype(test(     last, sun[last],         1)), void>{}, "");
+    static_assert(is_same<decltype(test(     last, sun[last],       1_d)), void>{}, "");
+    static_assert(is_same<decltype(test(     last, sun[last],       jan)), void>{}, "");
+    static_assert(is_same<decltype(test(     last, sun[last],       1_y)), void>{}, "");
+    static_assert(is_same<decltype(test(     last, sun[last],      last)), void>{}, "");
+    static_assert(is_same<decltype(test(     last, sun[last],    sun[1])), void>{}, "");
+    static_assert(is_same<decltype(test(     last, sun[last], sun[last])), void>{}, "");
+
+    static_assert(is_same<decltype(test(   sun[1],         1,         1)), year_month_weekday>{}, "");
+    static_assert(is_same<decltype(test(   sun[1],         1,       1_d)), void>{}, "");
+    static_assert(is_same<decltype(test(   sun[1],         1,       jan)), void>{}, "");
+    static_assert(is_same<decltype(test(   sun[1],         1,       1_y)), year_month_weekday>{}, "");
+    static_assert(is_same<decltype(test(   sun[1],         1,      last)), void>{}, "");
+    static_assert(is_same<decltype(test(   sun[1],         1,    sun[1])), void>{}, "");
+    static_assert(is_same<decltype(test(   sun[1],         1, sun[last])), void>{}, "");
+
+    static_assert(is_same<decltype(test(   sun[1],       1_d,         1)), void>{}, "");
+    static_assert(is_same<decltype(test(   sun[1],       1_d,       1_d)), void>{}, "");
+    static_assert(is_same<decltype(test(   sun[1],       1_d,       jan)), void>{}, "");
+    static_assert(is_same<decltype(test(   sun[1],       1_d,       1_y)), void>{}, "");
+    static_assert(is_same<decltype(test(   sun[1],       1_d,      last)), void>{}, "");
+    static_assert(is_same<decltype(test(   sun[1],       1_d,    sun[1])), void>{}, "");
+    static_assert(is_same<decltype(test(   sun[1],       1_d, sun[last])), void>{}, "");
+
+    static_assert(is_same<decltype(test(   sun[1],       jan,         1)), year_month_weekday>{}, "");
+    static_assert(is_same<decltype(test(   sun[1],       jan,       1_d)), void>{}, "");
+    static_assert(is_same<decltype(test(   sun[1],       jan,       jan)), void>{}, "");
+    static_assert(is_same<decltype(test(   sun[1],       jan,       1_y)), year_month_weekday>{}, "");
+    static_assert(is_same<decltype(test(   sun[1],       jan,      last)), void>{}, "");
+    static_assert(is_same<decltype(test(   sun[1],       jan,    sun[1])), void>{}, "");
+    static_assert(is_same<decltype(test(   sun[1],       jan, sun[last])), void>{}, "");
+
+    static_assert(is_same<decltype(test(   sun[1],       1_y,         1)), void>{}, "");
+    static_assert(is_same<decltype(test(   sun[1],       1_y,       1_d)), void>{}, "");
+    static_assert(is_same<decltype(test(   sun[1],       1_y,       jan)), void>{}, "");
+    static_assert(is_same<decltype(test(   sun[1],       1_y,       1_y)), void>{}, "");
+    static_assert(is_same<decltype(test(   sun[1],       1_y,      last)), void>{}, "");
+    static_assert(is_same<decltype(test(   sun[1],       1_y,    sun[1])), void>{}, "");
+    static_assert(is_same<decltype(test(   sun[1],       1_y, sun[last])), void>{}, "");
+
+    static_assert(is_same<decltype(test(   sun[1],      last,         1)), void>{}, "");
+    static_assert(is_same<decltype(test(   sun[1],      last,       1_d)), void>{}, "");
+    static_assert(is_same<decltype(test(   sun[1],      last,       jan)), void>{}, "");
+    static_assert(is_same<decltype(test(   sun[1],      last,       1_y)), void>{}, "");
+    static_assert(is_same<decltype(test(   sun[1],      last,      last)), void>{}, "");
+    static_assert(is_same<decltype(test(   sun[1],      last,    sun[1])), void>{}, "");
+    static_assert(is_same<decltype(test(   sun[1],      last, sun[last])), void>{}, "");
+
+    static_assert(is_same<decltype(test(   sun[1],    sun[1],         1)), void>{}, "");
+    static_assert(is_same<decltype(test(   sun[1],    sun[1],       1_d)), void>{}, "");
+    static_assert(is_same<decltype(test(   sun[1],    sun[1],       jan)), void>{}, "");
+    static_assert(is_same<decltype(test(   sun[1],    sun[1],       1_y)), void>{}, "");
+    static_assert(is_same<decltype(test(   sun[1],    sun[1],      last)), void>{}, "");
+    static_assert(is_same<decltype(test(   sun[1],    sun[1],    sun[1])), void>{}, "");
+    static_assert(is_same<decltype(test(   sun[1],    sun[1], sun[last])), void>{}, "");
+
+    static_assert(is_same<decltype(test(   sun[1], sun[last],         1)), void>{}, "");
+    static_assert(is_same<decltype(test(   sun[1], sun[last],       1_d)), void>{}, "");
+    static_assert(is_same<decltype(test(   sun[1], sun[last],       jan)), void>{}, "");
+    static_assert(is_same<decltype(test(   sun[1], sun[last],       1_y)), void>{}, "");
+    static_assert(is_same<decltype(test(   sun[1], sun[last],      last)), void>{}, "");
+    static_assert(is_same<decltype(test(   sun[1], sun[last],    sun[1])), void>{}, "");
+    static_assert(is_same<decltype(test(   sun[1], sun[last], sun[last])), void>{}, "");
+
+    static_assert(is_same<decltype(test(sun[last],         1,         1)), year_month_weekday_last>{}, "");
+    static_assert(is_same<decltype(test(sun[last],         1,       1_d)), void>{}, "");
+    static_assert(is_same<decltype(test(sun[last],         1,       jan)), void>{}, "");
+    static_assert(is_same<decltype(test(sun[last],         1,       1_y)), year_month_weekday_last>{}, "");
+    static_assert(is_same<decltype(test(sun[last],         1,      last)), void>{}, "");
+    static_assert(is_same<decltype(test(sun[last],         1,    sun[1])), void>{}, "");
+    static_assert(is_same<decltype(test(sun[last],         1, sun[last])), void>{}, "");
+
+    static_assert(is_same<decltype(test(sun[last],       1_d,         1)), void>{}, "");
+    static_assert(is_same<decltype(test(sun[last],       1_d,       1_d)), void>{}, "");
+    static_assert(is_same<decltype(test(sun[last],       1_d,       jan)), void>{}, "");
+    static_assert(is_same<decltype(test(sun[last],       1_d,       1_y)), void>{}, "");
+    static_assert(is_same<decltype(test(sun[last],       1_d,      last)), void>{}, "");
+    static_assert(is_same<decltype(test(sun[last],       1_d,    sun[1])), void>{}, "");
+    static_assert(is_same<decltype(test(sun[last],       1_d, sun[last])), void>{}, "");
+
+    static_assert(is_same<decltype(test(sun[last],       jan,         1)), year_month_weekday_last>{}, "");
+    static_assert(is_same<decltype(test(sun[last],       jan,       1_d)), void>{}, "");
+    static_assert(is_same<decltype(test(sun[last],       jan,       jan)), void>{}, "");
+    static_assert(is_same<decltype(test(sun[last],       jan,       1_y)), year_month_weekday_last>{}, "");
+    static_assert(is_same<decltype(test(sun[last],       jan,      last)), void>{}, "");
+    static_assert(is_same<decltype(test(sun[last],       jan,    sun[1])), void>{}, "");
+    static_assert(is_same<decltype(test(sun[last],       jan, sun[last])), void>{}, "");
+
+    static_assert(is_same<decltype(test(sun[last],       1_y,         1)), void>{}, "");
+    static_assert(is_same<decltype(test(sun[last],       1_y,       1_d)), void>{}, "");
+    static_assert(is_same<decltype(test(sun[last],       1_y,       jan)), void>{}, "");
+    static_assert(is_same<decltype(test(sun[last],       1_y,       1_y)), void>{}, "");
+    static_assert(is_same<decltype(test(sun[last],       1_y,      last)), void>{}, "");
+    static_assert(is_same<decltype(test(sun[last],       1_y,    sun[1])), void>{}, "");
+    static_assert(is_same<decltype(test(sun[last],       1_y, sun[last])), void>{}, "");
+
+    static_assert(is_same<decltype(test(sun[last],      last,         1)), void>{}, "");
+    static_assert(is_same<decltype(test(sun[last],      last,       1_d)), void>{}, "");
+    static_assert(is_same<decltype(test(sun[last],      last,       jan)), void>{}, "");
+    static_assert(is_same<decltype(test(sun[last],      last,       1_y)), void>{}, "");
+    static_assert(is_same<decltype(test(sun[last],      last,      last)), void>{}, "");
+    static_assert(is_same<decltype(test(sun[last],      last,    sun[1])), void>{}, "");
+    static_assert(is_same<decltype(test(sun[last],      last, sun[last])), void>{}, "");
+
+    static_assert(is_same<decltype(test(sun[last],    sun[1],         1)), void>{}, "");
+    static_assert(is_same<decltype(test(sun[last],    sun[1],       1_d)), void>{}, "");
+    static_assert(is_same<decltype(test(sun[last],    sun[1],       jan)), void>{}, "");
+    static_assert(is_same<decltype(test(sun[last],    sun[1],       1_y)), void>{}, "");
+    static_assert(is_same<decltype(test(sun[last],    sun[1],      last)), void>{}, "");
+    static_assert(is_same<decltype(test(sun[last],    sun[1],    sun[1])), void>{}, "");
+    static_assert(is_same<decltype(test(sun[last],    sun[1], sun[last])), void>{}, "");
+
+    static_assert(is_same<decltype(test(sun[last], sun[last],         1)), void>{}, "");
+    static_assert(is_same<decltype(test(sun[last], sun[last],       1_d)), void>{}, "");
+    static_assert(is_same<decltype(test(sun[last], sun[last],       jan)), void>{}, "");
+    static_assert(is_same<decltype(test(sun[last], sun[last],       1_y)), void>{}, "");
+    static_assert(is_same<decltype(test(sun[last], sun[last],      last)), void>{}, "");
+    static_assert(is_same<decltype(test(sun[last], sun[last],    sun[1])), void>{}, "");
+    static_assert(is_same<decltype(test(sun[last], sun[last], sun[last])), void>{}, "");
+}
diff --git a/third_party/date-3.0.1/test/date_test/op_div_weekday_indexed_weekday_indexed.fail.cpp b/third_party/date-3.0.1/test/date_test/op_div_weekday_indexed_weekday_indexed.fail.cpp
new file mode 100644
index 00000000..38def30b
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/op_div_weekday_indexed_weekday_indexed.fail.cpp
@@ -0,0 +1,33 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// weekday_indexed / weekday_indexed not allowed
+
+#include "date.h"
+
+int
+main()
+{
+    using namespace date;
+
+    auto x = fri[2]/fri[2];
+}
diff --git a/third_party/date-3.0.1/test/date_test/op_div_weekday_last_weekday_last.fail.cpp b/third_party/date-3.0.1/test/date_test/op_div_weekday_last_weekday_last.fail.cpp
new file mode 100644
index 00000000..c4dba101
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/op_div_weekday_last_weekday_last.fail.cpp
@@ -0,0 +1,33 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// weekday_last / weekday_last not allowed
+
+#include "date.h"
+
+int
+main()
+{
+    using namespace date;
+
+    auto x = fri[last]/fri[last];
+}
diff --git a/third_party/date-3.0.1/test/date_test/op_div_year_month.pass.cpp b/third_party/date-3.0.1/test/date_test/op_div_year_month.pass.cpp
new file mode 100644
index 00000000..48ff6c6d
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/op_div_year_month.pass.cpp
@@ -0,0 +1,35 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// constexpr year_month operator/(const year& y, const month& m) noexcept;
+// constexpr year_month operator/(const year& y, int   m) noexcept;
+
+#include "date.h"
+
+int
+main()
+{
+    using namespace date;
+
+    static_assert(2015_y/aug == year_month{year{2015}, aug}, "");
+    static_assert(2015_y/8   == year_month{year{2015}, aug}, "");
+}
diff --git a/third_party/date-3.0.1/test/date_test/op_div_year_month_day.pass.cpp b/third_party/date-3.0.1/test/date_test/op_div_year_month_day.pass.cpp
new file mode 100644
index 00000000..96baa3f1
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/op_div_year_month_day.pass.cpp
@@ -0,0 +1,43 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// constexpr year_month_day operator/(const year_month& ym, const day& d) noexcept;
+// constexpr year_month_day operator/(const year_month& ym, int d) noexcept;
+// constexpr year_month_day operator/(const year& y, const month_day& md) noexcept;
+// constexpr year_month_day operator/(int  y, const month_day& md) noexcept;
+// constexpr year_month_day operator/(const month_day& md, const year& y) noexcept;
+// constexpr year_month_day operator/(const month_day& md, int  y) noexcept;
+
+#include "date.h"
+
+int
+main()
+{
+    using namespace date;
+
+    static_assert(  2015_y/aug/14_d   == year_month_day{year{2015}, month{8}, day{14}}, "");
+    static_assert(  2015_y/aug/14     == year_month_day{year{2015}, month{8}, day{14}}, "");
+    static_assert(  2015_y/(aug/14_d) == year_month_day{year{2015}, month{8}, day{14}}, "");
+    static_assert(    2015/(aug/14_d) == year_month_day{year{2015}, month{8}, day{14}}, "");
+    static_assert(aug/14_d/2015_y     == year_month_day{year{2015}, month{8}, day{14}}, "");
+    static_assert(aug/14_d/2015       == year_month_day{year{2015}, month{8}, day{14}}, "");
+}
diff --git a/third_party/date-3.0.1/test/date_test/op_div_year_month_day_last.pass.cpp b/third_party/date-3.0.1/test/date_test/op_div_year_month_day_last.pass.cpp
new file mode 100644
index 00000000..f98993bb
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/op_div_year_month_day_last.pass.cpp
@@ -0,0 +1,41 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// constexpr year_month_day_last operator/(const year_month& ym, last_spec) noexcept;
+// constexpr year_month_day_last operator/(const year& y, const month_day_last& mdl) noexcept;
+// constexpr year_month_day_last operator/(int y, const month_day_last& mdl) noexcept;
+// constexpr year_month_day_last operator/(const month_day_last& mdl, const year& y) noexcept;
+// constexpr year_month_day_last operator/(const month_day_last& mdl, int y) noexcept;
+
+#include "date.h"
+
+int
+main()
+{
+    using namespace date;
+
+    static_assert(2015_y/aug/last       == year_month_day_last{year{2015}, month_day_last{month{8}}}, "");
+    static_assert(    2015_y/(aug/last) == year_month_day_last{year{2015}, month_day_last{month{8}}}, "");
+    static_assert(      2015/(aug/last) == year_month_day_last{year{2015}, month_day_last{month{8}}}, "");
+    static_assert(  aug/last/2015_y     == year_month_day_last{year{2015}, month_day_last{month{8}}}, "");
+    static_assert(  aug/last/2015       == year_month_day_last{year{2015}, month_day_last{month{8}}}, "");
+}
diff --git a/third_party/date-3.0.1/test/date_test/op_div_year_month_weekday.pass.cpp b/third_party/date-3.0.1/test/date_test/op_div_year_month_weekday.pass.cpp
new file mode 100644
index 00000000..90f2f55a
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/op_div_year_month_weekday.pass.cpp
@@ -0,0 +1,41 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// constexpr year_month_weekday operator/(const year_month& ym, const weekday_indexed& wdi) noexcept;
+// constexpr year_month_weekday operator/(const year&        y, const month_weekday&   mwd) noexcept;
+// constexpr year_month_weekday operator/(int                y, const month_weekday&   mwd) noexcept;
+// constexpr year_month_weekday operator/(const month_weekday& mwd, const year&          y) noexcept;
+// constexpr year_month_weekday operator/(const month_weekday& mwd, int                  y) noexcept;
+
+#include "date.h"
+
+int
+main()
+{
+    using namespace date;
+
+    static_assert(2015_y/aug/fri[2]       == year_month_weekday{year{2015}, month{8}, weekday_indexed{weekday{5u}, 2}}, "");
+    static_assert(    2015_y/(aug/fri[2]) == year_month_weekday{year{2015}, month{8}, weekday_indexed{weekday{5u}, 2}}, "");
+    static_assert(      2015/(aug/fri[2]) == year_month_weekday{year{2015}, month{8}, weekday_indexed{weekday{5u}, 2}}, "");
+    static_assert(aug/fri[2]/2015_y       == year_month_weekday{year{2015}, month{8}, weekday_indexed{weekday{5u}, 2}}, "");
+    static_assert(aug/fri[2]/2015         == year_month_weekday{year{2015}, month{8}, weekday_indexed{weekday{5u}, 2}}, "");
+}
diff --git a/third_party/date-3.0.1/test/date_test/op_div_year_month_weekday_last.pass.cpp b/third_party/date-3.0.1/test/date_test/op_div_year_month_weekday_last.pass.cpp
new file mode 100644
index 00000000..63f80669
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/op_div_year_month_weekday_last.pass.cpp
@@ -0,0 +1,41 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// constexpr year_month_weekday_last operator/(const year_month& ym, const weekday_last& wdl) noexcept;
+// constexpr year_month_weekday_last operator/(const year& y, const month_weekday_last& mwdl) noexcept;
+// constexpr year_month_weekday_last operator/(int y, const month_weekday_last& mwdl) noexcept;
+// constexpr year_month_weekday_last operator/(const month_weekday_last& mwdl, const year& y) noexcept;
+// constexpr year_month_weekday_last operator/(const month_weekday_last& mwdl, int y) noexcept;
+
+#include "date.h"
+
+int
+main()
+{
+    using namespace date;
+
+    static_assert(   2015_y/aug/fri[last]       == year_month_weekday_last{year{2015}, month{8}, weekday_last{weekday{5u}}}, "");
+    static_assert(       2015_y/(aug/fri[last]) == year_month_weekday_last{year{2015}, month{8}, weekday_last{weekday{5u}}}, "");
+    static_assert(         2015/(aug/fri[last]) == year_month_weekday_last{year{2015}, month{8}, weekday_last{weekday{5u}}}, "");
+    static_assert(aug/fri[last]/2015_y          == year_month_weekday_last{year{2015}, month{8}, weekday_last{weekday{5u}}}, "");
+    static_assert(aug/fri[last]/2015            == year_month_weekday_last{year{2015}, month{8}, weekday_last{weekday{5u}}}, "");
+}
diff --git a/third_party/date-3.0.1/test/date_test/op_div_year_month_year_month.fail.cpp b/third_party/date-3.0.1/test/date_test/op_div_year_month_year_month.fail.cpp
new file mode 100644
index 00000000..73a9208e
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/op_div_year_month_year_month.fail.cpp
@@ -0,0 +1,33 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// year_month / year_month not allowed
+
+#include "date.h"
+
+int
+main()
+{
+    using namespace date;
+
+    auto x = (2015_y/aug)/(2015_y/aug);
+}
diff --git a/third_party/date-3.0.1/test/date_test/op_div_year_year.fail.cpp b/third_party/date-3.0.1/test/date_test/op_div_year_year.fail.cpp
new file mode 100644
index 00000000..c7054d01
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/op_div_year_year.fail.cpp
@@ -0,0 +1,33 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// year / year not allowed
+
+#include "date.h"
+
+int
+main()
+{
+    using namespace date;
+
+    auto x = 2015_y/2015_y;
+}
diff --git a/third_party/date-3.0.1/test/date_test/parse.pass.cpp b/third_party/date-3.0.1/test/date_test/parse.pass.cpp
new file mode 100644
index 00000000..a7fecfd0
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/parse.pass.cpp
@@ -0,0 +1,921 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// This test is meant to maintain a record of the sizeof each type.
+
+#include "date.h"
+#include <cassert>
+#include <sstream>
+
+void
+test_a()
+{
+    using namespace date;
+    {
+        // correct abbreviation
+        std::istringstream in{"Sun 2016-12-11"};
+        sys_days tp;
+        in >> parse("%a %F", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(!in.eof());
+        assert(tp == 2016_y/12/11);
+    }
+    {
+        // correct abbreviation
+        std::istringstream in{"Sun 2016-12-11"};
+        sys_days tp;
+        in >> parse("%A %F", tp);
+        // this may fail with libstdc++, see https://github.com/HowardHinnant/date/issues/388
+        // possible workaround: compile date.h with -DONLY_C_LOCALE=1
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(!in.eof());
+        assert(tp == 2016_y/12/11);
+    }
+    {
+        // correct full name
+        std::istringstream in{"Sunday 2016-12-11"};
+        sys_days tp;
+        in >> parse("%a %F", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(!in.eof());
+        assert(tp == 2016_y/12/11);
+    }
+    {
+        // correct full name
+        std::istringstream in{"Sunday 2016-12-11"};
+        sys_days tp;
+        in >> parse("%A %F", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(!in.eof());
+        assert(tp == 2016_y/12/11);
+    }
+    {
+        // not a valid name
+        std::istringstream in{"Dec 2016-12-11"};
+        sys_days tp;
+        in >> parse("%a %F", tp);
+        assert( in.fail());
+        assert(!in.bad());
+        assert(!in.eof());
+        assert(tp == 1970_y/1/1);
+    }
+    {
+        // wrong name
+        std::istringstream in{"Sat 2016-12-11"};
+        sys_days tp;
+        in >> parse("%a %F", tp);
+        assert( in.fail());
+        assert(!in.bad());
+        assert(!in.eof());
+        assert(tp == 1970_y/1/1);
+    }
+    {
+        // extra ws in input
+        std::istringstream in{"Sun  2016-12-11"};
+        sys_days tp;
+        in >> parse("%a %F", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(!in.eof());
+        assert(tp == 2016_y/12/11);
+    }
+    {
+        // extra ws in format
+        std::istringstream in{"Sun 2016-12-11"};
+        sys_days tp;
+        in >> parse("%a  %F", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(!in.eof());
+        assert(tp == 2016_y/12/11);
+    }
+}
+
+void
+test_b()
+{
+    using namespace date;
+    {
+        // correct abbreviation
+        std::istringstream in{"Dec 11 2016"};
+        sys_days tp;
+        in >> parse("%b %d %Y", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(!in.eof());
+        assert(tp == 2016_y/12/11);
+    }
+    {
+        // correct abbreviation
+        std::istringstream in{"Dec 11 2016"};
+        sys_days tp;
+        in >> parse("%B %d %Y", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(!in.eof());
+        assert(tp == 2016_y/12/11);
+    }
+    {
+        // correct abbreviation
+        std::istringstream in{"Dec 11 2016"};
+        sys_days tp;
+        in >> parse("%h %d %Y", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(!in.eof());
+        assert(tp == 2016_y/12/11);
+    }
+    {
+        // correct full name
+        std::istringstream in{"December 11 2016"};
+        sys_days tp;
+        in >> parse("%b %d %Y", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(!in.eof());
+        assert(tp == 2016_y/12/11);
+    }
+    {
+        // correct full name
+        std::istringstream in{"December 11 2016"};
+        sys_days tp;
+        in >> parse("%B %d %Y", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(!in.eof());
+        assert(tp == 2016_y/12/11);
+    }
+    {
+        // correct full name
+        std::istringstream in{"December 11 2016"};
+        sys_days tp;
+        in >> parse("%h %d %Y", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(!in.eof());
+        assert(tp == 2016_y/12/11);
+    }
+    {
+        // incorrect abbreviation
+        std::istringstream in{"Dece 11 2016"};
+        sys_days tp;
+        in >> parse("%b %d %Y", tp);
+        assert( in.fail());
+        assert(!in.bad());
+        assert(!in.eof());
+        assert(tp == 1970_y/1/1);
+    }
+}
+
+void
+test_c()
+{
+    using namespace date;
+    using namespace std::chrono;
+    {
+        // correct abbreviation
+        std::istringstream in{"Sun Dec 11 14:02:43 2016"};
+        sys_seconds tp;
+        in >> parse("%c", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(tp == sys_days{2016_y/12/11} + hours{14} + minutes{2} + seconds{43});
+    }
+}
+
+void
+test_x()
+{
+    using namespace date;
+    using namespace std::chrono;
+    {
+        // correct abbreviation
+        std::istringstream in{"12/11/16"};
+        sys_seconds tp;
+        in >> parse("%x", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(tp == sys_days{2016_y/12/11});
+    }
+}
+
+void
+test_X()
+{
+    using namespace date;
+    using namespace std::chrono;
+    {
+        // correct abbreviation
+        std::istringstream in{"2016-12-11 14:02:43"};
+        sys_seconds tp;
+        in >> parse("%F %X", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(tp == sys_days{2016_y/12/11} + hours{14} + minutes{2} + seconds{43});
+    }
+}
+
+void
+test_C()
+{
+    using namespace date;
+    using namespace std::chrono;
+    {
+        std::istringstream in{"20 16 12 11"};
+        sys_days tp;
+        in >> parse("%C %y %m %d", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(tp == 2016_y/12/11);
+    }
+    {
+        std::istringstream in{"-2 1 12 11"};
+        sys_days tp;
+        in >> parse("%C %y %m %d", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(tp == -101_y/12/11);
+    }
+    {
+        std::istringstream in{"-1 0 12 11"};
+        sys_days tp;
+        in >> parse("%C %y %m %d", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(tp == -100_y/12/11);
+    }
+    {
+        std::istringstream in{"-1 99 12 11"};
+        sys_days tp;
+        in >> parse("%C %y %m %d", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(tp == -99_y/12/11);
+    }
+    {
+        std::istringstream in{"-1 1 12 11"};
+        sys_days tp;
+        in >> parse("%C %y %m %d", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(tp == -1_y/12/11);
+    }
+    {
+        std::istringstream in{"0 0 12 11"};
+        sys_days tp;
+        in >> parse("%C %y %m %d", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(tp == 0_y/12/11);
+    }
+    {
+        std::istringstream in{"0 1 12 11"};
+        sys_days tp;
+        in >> parse("%C %y %m %d", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(tp == 1_y/12/11);
+    }
+    {
+        std::istringstream in{"0 99 12 11"};
+        sys_days tp;
+        in >> parse("%C %y %m %d", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(tp == 99_y/12/11);
+    }
+    {
+        std::istringstream in{"1 0 12 11"};
+        sys_days tp;
+        in >> parse("%C %y %m %d", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(tp == 100_y/12/11);
+    }
+    {
+        std::istringstream in{"1 1 12 11"};
+        sys_days tp;
+        in >> parse("%C %y %m %d", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(tp == 101_y/12/11);
+    }
+}
+
+void
+test_d()
+{
+    using namespace date;
+    using namespace std::chrono;
+    {
+        std::istringstream in{"2016 09 12"};
+        sys_days tp;
+        in >> parse("%Y %d %m", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(tp == 2016_y/12/9);
+    }
+    {
+        std::istringstream in{"2016 09 12"};
+        sys_days tp;
+        in >> parse("%Y %e %m", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(tp == 2016_y/12/9);
+    }
+    {
+        std::istringstream in{"2016 9 12"};
+        sys_days tp;
+        in >> parse("%Y %d %m", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(tp == 2016_y/12/9);
+    }
+    {
+        std::istringstream in{"2016 9 12"};
+        sys_days tp;
+        in >> parse("%Y %e %m", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(tp == 2016_y/12/9);
+    }
+    {
+        std::istringstream in{"2016 31 11"};
+        sys_days tp;
+        in >> parse("%Y %e %m", tp);
+        assert(in.fail());
+    }
+}
+
+void
+test_D()
+{
+    using namespace date;
+    using namespace std::chrono;
+    {
+        std::istringstream in{"12/11/16"};
+        sys_days tp;
+        in >> parse("%D", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(tp == 2016_y/12/11);
+    }
+}
+
+void
+test_F()
+{
+    using namespace date;
+    using namespace std::chrono;
+    {
+        std::istringstream in{"2016-12-13"};
+        sys_days tp;
+        in >> parse("%F", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(tp == 2016_y/12/13);
+    }
+    {
+        std::istringstream in{"2016-12-13"};
+        year_month_day tp;
+        in >> parse("%F", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(tp == 2016_y/12/13);
+    }
+}
+
+void
+test_H()
+{
+    using namespace date;
+    using namespace std::chrono;
+    {
+        std::istringstream in{"2016-12-11 15"};
+        sys_time<hours> tp;
+        in >> parse("%F %H", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(tp == sys_days{2016_y/12/11} + hours{15});
+    }
+    {
+        std::istringstream in{"2016-12-11 24"};
+        sys_time<hours> tp;
+        in >> parse("%F %H", tp);
+        assert(in.fail());
+    }
+}
+
+void
+test_Ip()
+{
+    using namespace date;
+    using namespace std::chrono;
+    {
+        std::istringstream in{"2016-12-11 1 pm"};
+        sys_time<hours> tp;
+        in >> parse("%F %I %p", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(tp == sys_days{2016_y/12/11} + hours{13});
+    }
+    {
+        std::istringstream in{"2016-12-11 1 am"};
+        sys_time<hours> tp;
+        in >> parse("%F %I %p", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(tp == sys_days{2016_y/12/11} + hours{1});
+    }
+    {
+        std::istringstream in{"2016-12-11 13 am"};
+        sys_time<hours> tp;
+        in >> parse("%F %I %p", tp);
+        assert(in.fail());
+    }
+}
+
+void
+test_j()
+{
+    using namespace date;
+    using namespace std::chrono;
+    {
+        std::istringstream in{"2016 361"};
+        sys_days tp;
+        in >> parse("%Y %j", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(tp == sys_days{2016_y/12/26});
+    }
+}
+
+void
+test_m()
+{
+    using namespace date;
+    using namespace std::chrono;
+    {
+        std::istringstream in{"2016 12 09"};
+        sys_days tp;
+        in >> parse("%Y %d %m", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(tp == 2016_y/9/12);
+    }
+    {
+        std::istringstream in{"2016 12 9"};
+        sys_days tp;
+        in >> parse("%Y %d %m", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(tp == 2016_y/9/12);
+    }
+    {
+        std::istringstream in{"2016 12 13"};
+        sys_days tp;
+        in >> parse("%Y %d %m", tp);
+        assert(in.fail());
+    }
+}
+
+void
+test_M()
+{
+    using namespace date;
+    using namespace std::chrono;
+    {
+        std::istringstream in{"2016-12-11 15"};
+        sys_time<minutes> tp;
+        in >> parse("%F %M", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(tp == sys_days{2016_y/12/11} + minutes{15});
+    }
+    {
+        std::istringstream in{"2016-12-11 65"};
+        sys_time<minutes> tp;
+        in >> parse("%F %M", tp);
+        assert(in.fail());
+    }
+}
+
+void
+test_S()
+{
+    using namespace date;
+    using namespace std::chrono;
+    {
+        std::istringstream in{"2016-12-11 15"};
+        sys_seconds tp;
+        in >> parse("%F %S", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(tp == sys_days{2016_y/12/11} + seconds{15});
+    }
+    {
+        std::istringstream in{"2016-12-11 15.001"};
+        sys_time<milliseconds> tp;
+        in >> parse("%F %S", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(tp == sys_days{2016_y/12/11} + seconds{15} + milliseconds{1});
+    }
+    {
+        std::istringstream in{"2016-12-11 60"};
+        sys_seconds tp;
+        in >> parse("%F %S", tp);
+        assert(in.fail());
+    }
+}
+
+void
+test_T()
+{
+    using namespace date;
+    using namespace std::chrono;
+    {
+        std::istringstream in{"2016-12-11 15:43:22"};
+        sys_seconds tp;
+        in >> parse("%F %T", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(tp == sys_days{2016_y/12/11} + hours{15} + minutes{43} + seconds{22});
+    }
+    {
+        std::istringstream in{"2016-12-11 15:43:22.001"};
+        sys_time<milliseconds> tp;
+        in >> parse("%F %T", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(tp == sys_days{2016_y/12/11} + hours{15} + minutes{43} + seconds{22} +
+                                              milliseconds{1});
+    }
+    {
+        std::istringstream in{"2016-12-11 15:43:22"};
+        sys_time<milliseconds> tp;
+        in >> parse("%F %T", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(tp == sys_days{2016_y/12/11} + hours{15} + minutes{43} + seconds{22});
+    }
+    {
+        std::istringstream in{"15:43:22.001"};
+        milliseconds d;
+        in >> parse("%T", d);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(d == hours{15} + minutes{43} + seconds{22} + milliseconds{1});
+    }
+    {
+        std::istringstream in{"2016-12-11 24:43:22"};
+        sys_seconds tp;
+        in >> parse("%F %T", tp);
+        assert(in.fail());
+    }
+    {
+        std::istringstream in{"2016-12-11 15:60:22"};
+        sys_seconds tp;
+        in >> parse("%F %T", tp);
+        assert(in.fail());
+    }
+    {
+        std::istringstream in{"2016-12-11 15:43:60"};
+        sys_seconds tp;
+        in >> parse("%F %T", tp);
+        assert(in.fail());
+    }
+}
+
+void
+test_p()
+{
+    using namespace date;
+    using namespace std::chrono;
+    {
+        std::istringstream in{"2016-12-11 11pm"};
+        sys_time<hours> tp;
+        in >> parse("%F %I%p", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(tp == sys_days{2016_y/12/11} + hours{23});
+    }
+    {
+        std::istringstream in{"1986-12-01 01:01:01 pm"};
+        sys_time<seconds> tp;
+        in >> parse("%Y-%m-%d %I:%M:%S %p", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(tp == sys_days{1986_y/12/01} + hours{13} + minutes{01} + seconds{01});
+    }
+    {
+        std::istringstream in{"1986-12-01 01:01:01"};
+        sys_time<seconds> tp;
+        in >> parse("%Y-%m-%d %I:%M:%S", tp);
+        // The test will fail because %I needs the %p option to shows if it is AM or PM
+        assert(in.fail());
+    }
+}
+
+void
+test_r()
+{
+    using namespace date;
+    using namespace std::chrono;
+    {
+        std::istringstream in{"2016-12-26 1:36:57 pm"};
+        sys_seconds tp;
+        in >> parse("%F %r", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(tp == sys_days{2016_y/12/26} + hours{13} + minutes{36} + seconds{57});
+    }
+}
+
+void
+test_R()
+{
+    using namespace date;
+    using namespace std::chrono;
+    {
+        std::istringstream in{"2016-12-26 13:36"};
+        sys_seconds tp;
+        in >> parse("%F %R", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(tp == sys_days{2016_y/12/26} + hours{13} + minutes{36});
+    }
+}
+
+void
+test_U()
+{
+    using namespace date;
+    using namespace std::chrono;
+    {
+        std::istringstream in{"2016-52-1"};
+        sys_days tp;
+        in >> parse("%Y-%U-%w", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(tp == sys_days{2016_y/12/26});
+    }
+}
+
+void
+test_W()
+{
+    using namespace date;
+    using namespace std::chrono;
+    {
+        std::istringstream in{"2016-52-1"};
+        sys_days tp;
+        in >> parse("%Y-%W-%w", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(tp == sys_days{2016_y/12/26});
+    }
+}
+
+void
+test_GV()
+{
+    using namespace date;
+    using namespace std::chrono;
+    {
+        std::istringstream in{"2016-52-1"};
+        sys_days tp;
+        in >> parse("%G-%V-%w", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(tp == sys_days{2016_y/12/26});
+    }
+    {
+        std::istringstream in{"2016-52-1"};
+        sys_days tp;
+        in >> parse("%G-%V-%w", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(tp == sys_days{2016_y/12/26});
+    }
+    {
+        std::istringstream in{"20 16-52-1"};
+        sys_days tp;
+        in >> parse("%C %g-%V-%w", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(tp == sys_days{2016_y/12/26});
+    }
+    {
+        std::istringstream in{"20 16-52-1"};
+        sys_days tp;
+        in >> parse("%C %g-%V-%u", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(tp == sys_days{2016_y/12/26});
+    }
+}
+
+void
+test_z()
+{
+    using namespace date;
+    using namespace std::chrono;
+    {
+        std::istringstream in{"2016-12-26 15:53:22 -0500"};
+        sys_seconds tp;
+        in >> parse("%F %T %z", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(tp == sys_days{2016_y/12/26} + hours{20} + minutes{53} + seconds{22});
+    }
+    {
+        std::istringstream in{"2016-12-26 15:53:22 -0500"};
+        local_seconds tp;
+        in >> parse("%F %T %z", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(tp == local_days{2016_y/12/26} + hours{15} + minutes{53} + seconds{22});
+    }
+    {
+        std::istringstream in{"2016-12-26 15:53:22 -05:00"};
+        sys_seconds tp;
+        in >> parse("%F %T %Ez", tp);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(tp == sys_days{2016_y/12/26} + hours{20} + minutes{53} + seconds{22});
+    }
+}
+
+void
+test_Z()
+{
+    using namespace date;
+    using namespace std::chrono;
+    {
+        std::string a;
+        std::istringstream in{"2016-12-26 15:53:22 word"};
+        local_seconds tp;
+        in >> parse("%F %T %Z", tp, a);
+        assert(!in.fail());
+        assert(!in.bad());
+        assert(tp == local_days{2016_y/12/26} + hours{15} + minutes{53} + seconds{22});
+        assert(a == "word");
+    }
+}
+
+void
+test_trailing_Z()
+{
+    std::string format = "%FT%TZ";
+    std::string datetime = "2017-2-15T13:13:13";
+    std::istringstream input(datetime);
+    date::sys_seconds tp;
+    input >> date::parse(format, tp);
+    assert(input.fail());
+    assert(input.eof());
+}
+
+void
+test_leading_ws()
+{
+    using namespace std;
+    using namespace date;
+    istringstream in{"05/04/17 5/4/17"};
+    year_month_day d1, d2;
+    in >> parse("%D", d1) >> parse("%n%D", d2);
+    assert(d1 == may/4/2017);
+    assert(d2 == may/4/2017);
+}
+
+void
+test_space()
+{
+    using namespace std;
+    using namespace date;
+    {
+        istringstream in{"05/04/17"};
+        year_month_day d1;
+        in >> parse(" %D", d1);
+        assert(d1 == may/4/2017);
+    }
+    {
+        istringstream in{" 05/04/17"};
+        year_month_day d1;
+        in >> parse(" %D", d1);
+        assert(d1 == may/4/2017);
+    }
+    {
+        istringstream in{"  05/04/17"};
+        year_month_day d1;
+        in >> parse(" %D", d1);
+        assert(d1 == may/4/2017);
+    }
+}
+
+void
+test_n()
+{
+    using namespace std;
+    using namespace date;
+    {
+        istringstream in{"05/04/17"};
+        year_month_day d1;
+        in >> parse("%n%D", d1);
+        assert(in.fail());
+    }
+    {
+        istringstream in{" 05/04/17"};
+        year_month_day d1;
+        in >> parse("%n%D", d1);
+        assert(d1 == may/4/2017);
+    }
+    {
+        istringstream in{"  05/04/17"};
+        year_month_day d1;
+        in >> parse("%n%D", d1);
+        assert(in.fail());
+    }
+}
+
+void
+test_t()
+{
+    using namespace std;
+    using namespace date;
+    {
+        istringstream in{"05/04/17"};
+        year_month_day d1;
+        in >> parse("%t%D", d1);
+        assert(d1 == may/4/2017);
+    }
+    {
+        istringstream in{" 05/04/17"};
+        year_month_day d1;
+        in >> parse("%t%D", d1);
+        assert(d1 == may/4/2017);
+    }
+    {
+        istringstream in{"  05/04/17"};
+        year_month_day d1;
+        in >> parse("%t%D", d1);
+        assert(in.fail());
+    }
+}
+
+int
+main()
+{
+    test_a();
+    test_b();
+    test_c();
+    test_C();
+    test_d();
+    test_D();
+    test_F();
+    test_H();
+    test_Ip();
+    test_j();
+    test_m();
+    test_M();
+    test_p();
+    test_r();
+    test_R();
+    test_S();
+    test_T();
+    test_U();
+    test_W();
+    test_GV();
+    test_x();
+    test_X();
+    test_z();
+    test_Z();
+    test_trailing_Z();
+    test_leading_ws();
+    test_space();
+    test_n();
+    test_t();
+}
diff --git a/third_party/date-3.0.1/test/date_test/sizeof.pass.cpp b/third_party/date-3.0.1/test/date_test/sizeof.pass.cpp
new file mode 100644
index 00000000..1d91b667
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/sizeof.pass.cpp
@@ -0,0 +1,62 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// This test is meant to maintain a record of the sizeof each type.
+
+#include "date.h"
+
+int
+main()
+{
+    using namespace date;
+
+    static_assert(sizeof(days)                    == 4, "");
+    static_assert(sizeof(weeks)                   == 4, "");
+    static_assert(sizeof(months)                  == 4, "");
+    static_assert(sizeof(years)                   == 4, "");
+
+    static_assert(sizeof(sys_days)               == 4, "");
+
+    static_assert(sizeof(last_spec)               == 1, "");
+
+    static_assert(sizeof(day)                     == 1, "");
+    static_assert(sizeof(month)                   == 1, "");
+    static_assert(sizeof(year)                    == 2, "");
+
+    static_assert(sizeof(weekday)                 == 1, "");
+    static_assert(sizeof(weekday_indexed)         == 1, "");
+    static_assert(sizeof(weekday_last)            == 1, "");
+
+    static_assert(sizeof(month_day)               == 2, "");
+    static_assert(sizeof(month_day_last)          == 1, "");
+    static_assert(sizeof(month_weekday)           == 2, "");
+    static_assert(sizeof(month_weekday_last)      == 2, "");
+
+    static_assert(sizeof(year_month)              == 4, "");
+
+    static_assert(sizeof(year_month_day)          == 4, "");
+    static_assert(sizeof(year_month_day_last)     == 4, "");
+    static_assert(sizeof(year_month_weekday)      == 4, "");
+    static_assert(sizeof(year_month_weekday_last) == 4, "");
+
+    // sizeof time_of_day varies
+}
diff --git a/third_party/date-3.0.1/test/date_test/time_of_day_hours.pass.cpp b/third_party/date-3.0.1/test/date_test/time_of_day_hours.pass.cpp
new file mode 100644
index 00000000..5b12429c
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/time_of_day_hours.pass.cpp
@@ -0,0 +1,94 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// enum {am = 1, pm};
+
+// class time_of_day<std::chrono::hours>
+// {
+// public:
+//     using precision = std::chrono::hours;
+//
+//     constexpr explicit time_of_day(std::chrono::hours since_midnight) noexcept;
+//     constexpr time_of_day(std::chrono::hours h, unsigned md) noexcept;
+//
+//     constexpr std::chrono::hours hours() const noexcept;
+//     constexpr unsigned mode() const noexcept;
+//
+//     constexpr explicit operator precision() const noexcept;
+//     constexpr precision to_duration() const noexcept;
+//
+//     void make24() noexcept;
+//     void make12() noexcept;
+// };
+
+// std::ostream& operator<<(std::ostream& os, const time_of_day<std::chrono::hours>& t);
+
+#include "date.h"
+
+#include <cassert>
+#include <sstream>
+#include <type_traits>
+
+int
+main()
+{
+    using namespace date;
+    using namespace std;
+    using namespace std::chrono;
+
+    using tod = time_of_day<hours>;
+
+    static_assert(is_same<tod::precision::period, seconds::period>{}, "");
+
+    static_assert( is_trivially_destructible<tod>{}, "");
+    static_assert( is_default_constructible<tod>{}, "");
+    static_assert( is_trivially_copy_constructible<tod>{}, "");
+    static_assert( is_trivially_copy_assignable<tod>{}, "");
+    static_assert( is_trivially_move_constructible<tod>{}, "");
+    static_assert( is_trivially_move_assignable<tod>{}, "");
+
+    static_assert(is_nothrow_constructible<tod, hours>{}, "");
+    static_assert(!is_convertible<hours, tod>{}, "");
+
+    static_assert(is_nothrow_constructible<tod::precision, tod>{}, "");
+    static_assert(!is_convertible<tod, tod::precision>{}, "");
+
+    constexpr tod t1 = tod{hours{13}};
+    static_assert(t1.hours() == hours{13}, "");
+#if __cplusplus >= 201402
+    static_assert(static_cast<tod::precision>(t1) == hours{13}, "");
+    static_assert(t1.to_duration() == hours{13}, "");
+#endif
+
+    auto t2 = t1;
+    assert(t2.hours() == t1.hours());
+    assert(t2.to_duration() == t1.to_duration());
+    ostringstream os;
+    os << t2;
+    assert(os.str() == "13:00:00");
+    auto h = make12(t2.hours());
+    os.str("");
+    assert(h == hours{1});
+    assert(t2.to_duration() == t1.to_duration());
+    assert(!is_am(t2.hours()));
+    assert(is_pm(t2.hours()));
+}
diff --git a/third_party/date-3.0.1/test/date_test/time_of_day_microfortnights.pass.cpp b/third_party/date-3.0.1/test/date_test/time_of_day_microfortnights.pass.cpp
new file mode 100644
index 00000000..362c793c
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/time_of_day_microfortnights.pass.cpp
@@ -0,0 +1,111 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// enum {am = 1, pm};
+
+// template <class Rep, class Period>
+// class time_of_day<std::chrono::duration<Rep, Period>>
+// {
+// public:
+//     using precision = std::chrono::std::chrono::duration<Rep, Period>;
+//
+//     constexpr explicit time_of_day(precision since_midnight) noexcept;
+//     constexpr time_of_day(std::chrono::hours h, std::chrono::minutes m,
+//                           std::chrono::seconds s, precision sub_s,
+//                           unsigned md) noexcept;
+//
+//     constexpr std::chrono::hours hours() const noexcept;
+//     constexpr std::chrono::minutes minutes() const noexcept;
+//     constexpr std::chrono::seconds seconds() const noexcept;
+//     constexpr precision subseconds() const noexcept;
+//     constexpr unsigned mode() const noexcept;
+//
+//     constexpr explicit operator precision() const noexcept;
+//     constexpr precision to_duration() const noexcept;
+//
+//     void make24() noexcept;
+//     void make12() noexcept;
+// };
+
+// template <class Rep, class Period>
+// std::ostream&
+// operator<<(std::ostream& os, const time_of_day<std::chrono::duration<Rep, Period>>& t);
+
+#include "date.h"
+
+#include <cassert>
+#include <sstream>
+#include <type_traits>
+
+using fortnights = std::chrono::duration<date::weeks::rep,
+                                         date::detail::ratio_multiply<std::ratio<2>,
+                                                                      date::weeks::period>>;
+
+using microfortnights = std::chrono::duration<std::int64_t,
+                                              date::detail::ratio_multiply<fortnights::period,
+                                                                           std::micro>>;
+
+int
+main()
+{
+    using namespace date;
+    using namespace std;
+    using namespace std::chrono;
+
+    using tod = time_of_day<typename common_type<hours, minutes, microfortnights>::type>;
+
+    static_assert(is_same<tod::precision::period, ratio<1, 10000>>{}, "");
+
+    static_assert( is_trivially_destructible<tod>{}, "");
+    static_assert( is_default_constructible<tod>{}, "");
+    static_assert( is_trivially_copy_constructible<tod>{}, "");
+    static_assert( is_trivially_copy_assignable<tod>{}, "");
+    static_assert( is_trivially_move_constructible<tod>{}, "");
+    static_assert( is_trivially_move_assignable<tod>{}, "");
+
+    static_assert(is_constructible<tod, microfortnights>{}, "");
+    static_assert(!is_convertible<microfortnights, tod>{}, "");
+
+    static_assert(is_nothrow_constructible<tod::precision, tod>{}, "");
+    static_assert(!is_convertible<tod, tod::precision>{}, "");
+
+    constexpr tod t1 = tod{hours{13} + minutes{7} + microfortnights{5}};
+    static_assert(t1.hours() == hours{13}, "");
+    static_assert(t1.minutes() == minutes{7}, "");
+    static_assert(t1.seconds() == seconds{6}, "");
+    static_assert(t1.subseconds() == tod::precision{480}, "");
+#if __cplusplus >= 201402
+    static_assert(static_cast<tod::precision>(t1) == hours{13} + minutes{7}
+                                                     + microfortnights{5}, "");
+    static_assert(t1.to_duration() == hours{13} + minutes{7} + microfortnights{5}, "");
+#endif
+
+    auto t2 = t1;
+    assert(t2.hours() == t1.hours());
+    assert(t2.minutes() == t1.minutes());
+    assert(t2.seconds() == t1.seconds());
+    assert(t2.subseconds() == t1.subseconds());
+    assert(t2.to_duration() == t1.to_duration());
+    ostringstream os;
+    os << t2;
+    assert(os.str() == "13:07:06.0480");
+}
diff --git a/third_party/date-3.0.1/test/date_test/time_of_day_milliseconds.pass.cpp b/third_party/date-3.0.1/test/date_test/time_of_day_milliseconds.pass.cpp
new file mode 100644
index 00000000..c13fe4c0
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/time_of_day_milliseconds.pass.cpp
@@ -0,0 +1,104 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// enum {am = 1, pm};
+
+// template <class Rep, class Period>
+// class time_of_day<std::chrono::duration<Rep, Period>>
+// {
+// public:
+//     using precision = std::chrono::std::chrono::duration<Rep, Period>;
+//
+//     constexpr explicit time_of_day(precision since_midnight) noexcept;
+//     constexpr time_of_day(std::chrono::hours h, std::chrono::minutes m,
+//                           std::chrono::seconds s, precision sub_s,
+//                           unsigned md) noexcept;
+//
+//     constexpr std::chrono::hours hours() const noexcept;
+//     constexpr std::chrono::minutes minutes() const noexcept;
+//     constexpr std::chrono::seconds seconds() const noexcept;
+//     constexpr precision subseconds() const noexcept;
+//     constexpr unsigned mode() const noexcept;
+//
+//     constexpr explicit operator precision() const noexcept;
+//     constexpr precision to_duration() const noexcept;
+//
+//     void make24() noexcept;
+//     void make12() noexcept;
+// };
+
+// template <class Rep, class Period>
+// std::ostream&
+// operator<<(std::ostream& os, const time_of_day<std::chrono::duration<Rep, Period>>& t);
+
+#include "date.h"
+
+#include <cassert>
+#include <sstream>
+#include <type_traits>
+
+int
+main()
+{
+    using namespace date;
+    using namespace std;
+    using namespace std::chrono;
+
+    using tod = time_of_day<milliseconds>;
+
+    static_assert(is_same<tod::precision::period, milliseconds::period>{}, "");
+
+    static_assert( is_trivially_destructible<tod>{}, "");
+    static_assert( is_default_constructible<tod>{}, "");
+    static_assert( is_trivially_copy_constructible<tod>{}, "");
+    static_assert( is_trivially_copy_assignable<tod>{}, "");
+    static_assert( is_trivially_move_constructible<tod>{}, "");
+    static_assert( is_trivially_move_assignable<tod>{}, "");
+
+    static_assert(is_nothrow_constructible<tod, milliseconds>{}, "");
+    static_assert(!is_convertible<milliseconds, tod>{}, "");
+
+    static_assert(is_nothrow_constructible<tod::precision, tod>{}, "");
+    static_assert(!is_convertible<tod, tod::precision>{}, "");
+
+    constexpr tod t1 = tod{hours{13} + minutes{7} + seconds{5} + milliseconds{22}};
+    static_assert(t1.hours() == hours{13}, "");
+    static_assert(t1.minutes() == minutes{7}, "");
+    static_assert(t1.seconds() == seconds{5}, "");
+    static_assert(t1.subseconds() == milliseconds{22}, "");
+#if __cplusplus >= 201402
+    static_assert(static_cast<tod::precision>(t1) == hours{13} + minutes{7}
+                                                     + seconds{5} + milliseconds{22}, "");
+    static_assert(t1.to_duration() == hours{13} + minutes{7} + seconds{5}
+                                    + milliseconds{22}, "");
+#endif
+
+    auto t2 = t1;
+    assert(t2.hours() == t1.hours());
+    assert(t2.minutes() == t1.minutes());
+    assert(t2.seconds() == t1.seconds());
+    assert(t2.subseconds() == t1.subseconds());
+    assert(t2.to_duration() == t1.to_duration());
+    ostringstream os;
+    os << t2;
+    assert(os.str() == "13:07:05.022");
+}
diff --git a/third_party/date-3.0.1/test/date_test/time_of_day_minutes.pass.cpp b/third_party/date-3.0.1/test/date_test/time_of_day_minutes.pass.cpp
new file mode 100644
index 00000000..47cdafca
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/time_of_day_minutes.pass.cpp
@@ -0,0 +1,92 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// enum {am = 1, pm};
+
+// class time_of_day<std::chrono::minutes>
+// {
+// public:
+//     using precision = std::chrono::minutes;
+//
+//     constexpr explicit time_of_day(std::chrono::minutes since_midnight) noexcept;
+//     constexpr time_of_day(std::chrono::hours h, std::chrono::minutes m,
+//                           unsigned md) noexcept;
+//
+//     constexpr std::chrono::hours hours() const noexcept;
+//     constexpr std::chrono::minutes minutes() const noexcept;
+//     constexpr unsigned mode() const noexcept;
+//
+//     constexpr explicit operator precision() const noexcept;
+//     constexpr precision to_duration() const noexcept;
+//
+//     void make24() noexcept;
+//     void make12() noexcept;
+// };
+
+// std::ostream& operator<<(std::ostream& os, const time_of_day<std::chrono::minutes>& t);
+
+#include "date.h"
+
+#include <cassert>
+#include <sstream>
+#include <type_traits>
+
+int
+main()
+{
+    using namespace date;
+    using namespace std;
+    using namespace std::chrono;
+
+    using tod = time_of_day<minutes>;
+
+    static_assert(is_same<tod::precision::period, seconds::period>{}, "");
+
+    static_assert( is_trivially_destructible<tod>{}, "");
+    static_assert( is_default_constructible<tod>{}, "");
+    static_assert( is_trivially_copy_constructible<tod>{}, "");
+    static_assert( is_trivially_copy_assignable<tod>{}, "");
+    static_assert( is_trivially_move_constructible<tod>{}, "");
+    static_assert( is_trivially_move_assignable<tod>{}, "");
+
+    static_assert(is_nothrow_constructible<tod, minutes>{}, "");
+    static_assert(!is_convertible<minutes, tod>{}, "");
+
+    static_assert(is_nothrow_constructible<tod::precision, tod>{}, "");
+    static_assert(!is_convertible<tod, tod::precision>{}, "");
+
+    constexpr tod t1 = tod{hours{13} + minutes{7}};
+    static_assert(t1.hours() == hours{13}, "");
+    static_assert(t1.minutes() == minutes{7}, "");
+#if __cplusplus >= 201402
+    static_assert(static_cast<tod::precision>(t1) == hours{13} + minutes{7}, "");
+    static_assert(t1.to_duration() == hours{13} + minutes{7}, "");
+#endif
+
+    auto t2 = t1;
+    assert(t2.hours() == t1.hours());
+    assert(t2.minutes() == t1.minutes());
+    assert(t2.to_duration() == t1.to_duration());
+    ostringstream os;
+    os << t2;
+    assert(os.str() == "13:07:00");
+}
diff --git a/third_party/date-3.0.1/test/date_test/time_of_day_nanoseconds.pass.cpp b/third_party/date-3.0.1/test/date_test/time_of_day_nanoseconds.pass.cpp
new file mode 100644
index 00000000..71a7fe8a
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/time_of_day_nanoseconds.pass.cpp
@@ -0,0 +1,104 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// enum {am = 1, pm};
+
+// template <class Rep, class Period>
+// class time_of_day<std::chrono::duration<Rep, Period>>
+// {
+// public:
+//     using precision = std::chrono::std::chrono::duration<Rep, Period>;
+//
+//     constexpr explicit time_of_day(precision since_midnight) noexcept;
+//     constexpr time_of_day(std::chrono::hours h, std::chrono::minutes m,
+//                           std::chrono::seconds s, precision sub_s,
+//                           unsigned md) noexcept;
+//
+//     constexpr std::chrono::hours hours() const noexcept;
+//     constexpr std::chrono::minutes minutes() const noexcept;
+//     constexpr std::chrono::seconds seconds() const noexcept;
+//     constexpr precision subseconds() const noexcept;
+//     constexpr unsigned mode() const noexcept;
+//
+//     constexpr explicit operator precision() const noexcept;
+//     constexpr precision to_duration() const noexcept;
+//
+//     void make24() noexcept;
+//     void make12() noexcept;
+// };
+
+// template <class Rep, class Period>
+// std::ostream&
+// operator<<(std::ostream& os, const time_of_day<std::chrono::duration<Rep, Period>>& t);
+
+#include "date.h"
+
+#include <cassert>
+#include <sstream>
+#include <type_traits>
+
+int
+main()
+{
+    using namespace date;
+    using namespace std;
+    using namespace std::chrono;
+
+    using tod = time_of_day<nanoseconds>;
+
+    static_assert(is_same<tod::precision::period, nanoseconds::period>{}, "");
+
+    static_assert( is_trivially_destructible<tod>{}, "");
+    static_assert( is_default_constructible<tod>{}, "");
+    static_assert( is_trivially_copy_constructible<tod>{}, "");
+    static_assert( is_trivially_copy_assignable<tod>{}, "");
+    static_assert( is_trivially_move_constructible<tod>{}, "");
+    static_assert( is_trivially_move_assignable<tod>{}, "");
+
+    static_assert(is_nothrow_constructible<tod, nanoseconds>{}, "");
+    static_assert(!is_convertible<nanoseconds, tod>{}, "");
+
+    static_assert(is_nothrow_constructible<tod::precision, tod>{}, "");
+    static_assert(!is_convertible<tod, tod::precision>{}, "");
+
+    constexpr tod t1 = tod{hours{13} + minutes{7} + seconds{5} + nanoseconds{22}};
+    static_assert(t1.hours() == hours{13}, "");
+    static_assert(t1.minutes() == minutes{7}, "");
+    static_assert(t1.seconds() == seconds{5}, "");
+    static_assert(t1.subseconds() == nanoseconds{22}, "");
+#if __cplusplus >= 201402
+    static_assert(static_cast<tod::precision>(t1) == hours{13} + minutes{7}
+                                                     + seconds{5} + nanoseconds{22}, "");
+    static_assert(t1.to_duration() == hours{13} + minutes{7} + seconds{5}
+                                    + nanoseconds{22}, "");
+#endif
+
+    auto t2 = t1;
+    assert(t2.hours() == t1.hours());
+    assert(t2.minutes() == t1.minutes());
+    assert(t2.seconds() == t1.seconds());
+    assert(t2.subseconds() == t1.subseconds());
+    assert(t2.to_duration() == t1.to_duration());
+    ostringstream os;
+    os << t2;
+    assert(os.str() == "13:07:05.000000022");
+}
diff --git a/third_party/date-3.0.1/test/date_test/time_of_day_seconds.pass.cpp b/third_party/date-3.0.1/test/date_test/time_of_day_seconds.pass.cpp
new file mode 100644
index 00000000..eaf4fb98
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/time_of_day_seconds.pass.cpp
@@ -0,0 +1,96 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// enum {am = 1, pm};
+
+// class time_of_day<std::chrono::seconds>
+// {
+// public:
+//     using precision = std::chrono::seconds;
+//
+//     constexpr explicit time_of_day(std::chrono::seconds since_midnight) noexcept;
+//     constexpr time_of_day(std::chrono::hours h, std::chrono::minutes m,
+//                           std::chrono::seconds s, unsigned md) noexcept;
+//
+//     constexpr std::chrono::hours hours() const noexcept;
+//     constexpr std::chrono::minutes minutes() const noexcept;
+//     constexpr std::chrono::seconds seconds() const noexcept;
+//     constexpr unsigned mode() const noexcept;
+//
+//     constexpr explicit operator precision() const noexcept;
+//     constexpr precision to_duration() const noexcept;
+//
+//     void make24() noexcept;
+//     void make12() noexcept;
+// };
+
+// std::ostream& operator<<(std::ostream& os, const time_of_day<std::chrono::seconds>& t);
+
+#include "date.h"
+
+#include <cassert>
+#include <sstream>
+#include <type_traits>
+
+int
+main()
+{
+    using namespace date;
+    using namespace std;
+    using namespace std::chrono;
+
+    using tod = time_of_day<seconds>;
+
+    static_assert(is_same<tod::precision::period, seconds::period>{}, "");
+
+    static_assert( is_trivially_destructible<tod>{}, "");
+    static_assert( is_default_constructible<tod>{}, "");
+    static_assert( is_trivially_copy_constructible<tod>{}, "");
+    static_assert( is_trivially_copy_assignable<tod>{}, "");
+    static_assert( is_trivially_move_constructible<tod>{}, "");
+    static_assert( is_trivially_move_assignable<tod>{}, "");
+
+    static_assert(is_nothrow_constructible<tod, seconds>{}, "");
+    static_assert(!is_convertible<seconds, tod>{}, "");
+
+    static_assert(is_nothrow_constructible<tod::precision, tod>{}, "");
+    static_assert(!is_convertible<tod, tod::precision>{}, "");
+
+    constexpr tod t1 = tod{hours{13} + minutes{7} + seconds{5}};
+    static_assert(t1.hours() == hours{13}, "");
+    static_assert(t1.minutes() == minutes{7}, "");
+    static_assert(t1.seconds() == seconds{5}, "");
+#if __cplusplus >= 201402
+    static_assert(static_cast<tod::precision>(t1) == hours{13} + minutes{7}
+                                                     + seconds{5}, "");
+    static_assert(t1.to_duration() == hours{13} + minutes{7} + seconds{5}, "");
+#endif
+
+    auto t2 = t1;
+    assert(t2.hours() == t1.hours());
+    assert(t2.minutes() == t1.minutes());
+    assert(t2.seconds() == t1.seconds());
+    assert(t2.to_duration() == t1.to_duration());
+    ostringstream os;
+    os << t2;
+    assert(os.str() == "13:07:05");
+}
diff --git a/third_party/date-3.0.1/test/date_test/weekday.pass.cpp b/third_party/date-3.0.1/test/date_test/weekday.pass.cpp
new file mode 100644
index 00000000..de31faff
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/weekday.pass.cpp
@@ -0,0 +1,201 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// class weekday
+// {
+//     unsigned char wd_;
+// public:
+//     explicit constexpr weekday(unsigned wd) noexcept;
+//     constexpr weekday(const sys_days& dp) noexcept;
+//
+//     weekday& operator++()    noexcept;
+//     weekday  operator++(int) noexcept;
+//     weekday& operator--()    noexcept;
+//     weekday  operator--(int) noexcept;
+//
+//     weekday& operator+=(const days& d) noexcept;
+//     weekday& operator-=(const days& d) noexcept;
+//
+//     constexpr explicit operator unsigned() const noexcept;
+//     constexpr bool ok() const noexcept;
+//
+//     // tested with weekday_indexed
+//     constexpr weekday_indexed operator[](unsigned index) const noexcept;
+//     // tested with weekday_last
+//     constexpr weekday_last    operator[](last_spec)      const noexcept;
+// };
+
+// constexpr bool operator==(const weekday& x, const weekday& y) noexcept;
+// constexpr bool operator!=(const weekday& x, const weekday& y) noexcept;
+
+// constexpr weekday operator+(const weekday& x, const days&    y) noexcept;
+// constexpr weekday operator+(const days&    x, const weekday& y) noexcept;
+// constexpr weekday operator-(const weekday& x, const days&    y) noexcept;
+// constexpr days    operator-(const weekday& x, const weekday& y) noexcept;
+
+// std::ostream& operator<<(std::ostream& os, const weekday& wd);
+
+// constexpr weekday sun{0};
+// constexpr weekday mon{1};
+// constexpr weekday tue{2};
+// constexpr weekday wed{3};
+// constexpr weekday thu{4};
+// constexpr weekday fri{5};
+// constexpr weekday sat{6};
+
+#include "date.h"
+
+#include <cassert>
+#include <sstream>
+#include <type_traits>
+
+static_assert( std::is_trivially_destructible<date::weekday>{}, "");
+static_assert( std::is_default_constructible<date::weekday>{}, "");
+static_assert( std::is_trivially_copy_constructible<date::weekday>{}, "");
+static_assert( std::is_trivially_copy_assignable<date::weekday>{}, "");
+static_assert( std::is_trivially_move_constructible<date::weekday>{}, "");
+static_assert( std::is_trivially_move_assignable<date::weekday>{}, "");
+
+static_assert( std::is_nothrow_constructible<date::weekday, unsigned>{}, "");
+static_assert( std::is_nothrow_constructible<date::weekday, date::sys_days>{}, "");
+static_assert(!std::is_convertible<unsigned, date::weekday>{}, "");
+static_assert( std::is_convertible<date::sys_days, date::weekday>{}, "");
+static_assert(!std::is_convertible<date::weekday, unsigned>{}, "");
+
+static_assert( date::weekday{0u}.ok(), "");
+static_assert( date::weekday{1u}.ok(), "");
+static_assert( date::weekday{2u}.ok(), "");
+static_assert( date::weekday{3u}.ok(), "");
+static_assert( date::weekday{4u}.ok(), "");
+static_assert( date::weekday{5u}.ok(), "");
+static_assert( date::weekday{6u}.ok(), "");
+static_assert( date::weekday{7u}.ok(), "");
+static_assert(!date::weekday{8u}.ok(), "");
+
+void
+test_weekday_arithmetic()
+{
+    using namespace date;
+    constexpr unsigned a[7][7] =
+    {// -    Sun Mon Tue Wed Thu Fri Sat
+     /*Sun*/ {0,  6,  5,  4,  3,  2,  1},
+     /*Mon*/ {1,  0,  6,  5,  4,  3,  2},
+     /*Tue*/ {2,  1,  0,  6,  5,  4,  3},
+     /*Wed*/ {3,  2,  1,  0,  6,  5,  4},
+     /*Thu*/ {4,  3,  2,  1,  0,  6,  5},
+     /*Fri*/ {5,  4,  3,  2,  1,  0,  6},
+     /*Sat*/ {6,  5,  4,  3,  2,  1,  0}
+    };
+    for (unsigned x = 0; x < 7; ++x)
+    {
+        for (unsigned y = 0; y < 7; ++y)
+        {
+            assert(weekday{x} - weekday{y} == days{a[x][y]});
+            assert(weekday{x} - days{a[x][y]} == weekday{y});
+            assert(weekday{x} == weekday{y} + days{a[x][y]});
+            assert(weekday{x} == days{a[x][y]} + weekday{y});
+        }
+    }
+    for (unsigned x = 0; x < 7; ++x)
+    {
+        for (int y = -21; y < 21; ++y)
+        {
+            weekday wx{x};
+            days dy{y};
+            wx += dy;
+            weekday wz = weekday{x} + days{y};
+            assert(wx.ok());
+            assert(wz.ok());
+            assert(wx == wz);
+            assert(wx - weekday{x} == days{y % 7 + (y % 7 < 0 ? 7 : 0)});
+        }
+    }
+    for (unsigned x = 0; x < 7; ++x)
+    {
+        for (int y = -21; y < 21; ++y)
+        {
+            weekday wx{x};
+            days dy{y};
+            wx -= dy;
+            assert(wx == weekday{x} + days{-y});
+        }
+    }
+    for (unsigned x = 0; x < 7; ++x)
+    {
+        weekday wx{x};
+        assert(++wx - weekday{x} == days{1});
+        assert(wx++ - weekday{x} == days{1});
+        assert(wx - weekday{x} == days{2});
+        assert(wx-- - weekday{x} == days{2});
+        assert(wx - weekday{x} == days{1});
+        assert(--wx - weekday{x} == days{0});
+    }
+}
+
+int
+main()
+{
+    using namespace date;
+
+    static_assert(sun == weekday{0u}, "");
+    static_assert(mon == weekday{1u}, "");
+    static_assert(tue == weekday{2u}, "");
+    static_assert(wed == weekday{3u}, "");
+    static_assert(thu == weekday{4u}, "");
+    static_assert(fri == weekday{5u}, "");
+    static_assert(sat == weekday{6u}, "");
+
+    static_assert(!(sun != sun), "");
+    static_assert(  sun != mon, "");
+    static_assert(  mon != sun, "");
+
+    test_weekday_arithmetic();
+
+    std::ostringstream os;
+
+    os << sun;
+    assert(os.str() == "Sun");
+    os.str("");
+
+    os << mon;
+    assert(os.str() == "Mon");
+    os.str("");
+
+    os << tue;
+    assert(os.str() == "Tue");
+    os.str("");
+
+    os << wed;
+    assert(os.str() == "Wed");
+    os.str("");
+
+    os << thu;
+    assert(os.str() == "Thu");
+    os.str("");
+
+    os << fri;
+    assert(os.str() == "Fri");
+    os.str("");
+
+    os << sat;
+    assert(os.str() == "Sat");
+}
diff --git a/third_party/date-3.0.1/test/date_test/weekday_indexed.pass.cpp b/third_party/date-3.0.1/test/date_test/weekday_indexed.pass.cpp
new file mode 100644
index 00000000..5d25d2bd
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/weekday_indexed.pass.cpp
@@ -0,0 +1,70 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// class weekday_indexed
+// {
+// public:
+//     weekday_indexed() = default;
+//     constexpr weekday_indexed(const date::weekday& wd, unsigned index) noexcept;
+//
+//     constexpr date::weekday weekday() const noexcept;
+//     constexpr unsigned index() const noexcept;
+//     constexpr bool ok() const noexcept;
+// };
+//
+// constexpr bool operator==(const weekday_indexed& x, const weekday_indexed& y) noexcept;
+// constexpr bool operator!=(const weekday_indexed& x, const weekday_indexed& y) noexcept;
+//
+// std::ostream& operator<<(std::ostream& os, const weekday_indexed& wdi);
+
+#include "date.h"
+
+#include <cassert>
+#include <sstream>
+#include <type_traits>
+
+static_assert( std::is_trivially_destructible<date::weekday_indexed>{}, "");
+static_assert( std::is_default_constructible<date::weekday_indexed>{}, "");
+static_assert( std::is_trivially_copy_constructible<date::weekday_indexed>{}, "");
+static_assert( std::is_trivially_copy_assignable<date::weekday_indexed>{}, "");
+static_assert( std::is_trivially_move_constructible<date::weekday_indexed>{}, "");
+static_assert( std::is_trivially_move_assignable<date::weekday_indexed>{}, "");
+
+static_assert(std::is_nothrow_constructible<date::weekday_indexed, date::weekday,
+                                                                   unsigned>{}, "");
+
+int
+main()
+{
+    using namespace date;
+
+    constexpr weekday_indexed wdi = sun[1];
+    static_assert(wdi.weekday() == sun, "");
+    static_assert(wdi.index() == 1, "");
+    static_assert(wdi.ok(), "");
+    static_assert(wdi == weekday_indexed{sun, 1}, "");
+    static_assert(wdi != weekday_indexed{sun, 2}, "");
+    static_assert(wdi != weekday_indexed{mon, 1}, "");
+    std::ostringstream os;
+    os << wdi;
+    assert(os.str() == "Sun[1]");
+}
diff --git a/third_party/date-3.0.1/test/date_test/weekday_last.pass.cpp b/third_party/date-3.0.1/test/date_test/weekday_last.pass.cpp
new file mode 100644
index 00000000..3c30bf71
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/weekday_last.pass.cpp
@@ -0,0 +1,66 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// class weekday_last
+// {
+// public:
+//     explicit constexpr weekday_last(const date::weekday& wd) noexcept;
+//
+//     constexpr date::weekday weekday() const noexcept;
+//     constexpr bool ok() const noexcept;
+// };
+//
+// constexpr bool operator==(const weekday_last& x, const weekday_last& y) noexcept;
+// constexpr bool operator!=(const weekday_last& x, const weekday_last& y) noexcept;
+//
+// std::ostream& operator<<(std::ostream& os, const weekday_last& wdl);
+
+#include "date.h"
+
+#include <cassert>
+#include <sstream>
+#include <type_traits>
+
+static_assert( std::is_trivially_destructible<date::weekday_last>{}, "");
+static_assert(!std::is_default_constructible<date::weekday_last>{}, "");
+static_assert( std::is_trivially_copy_constructible<date::weekday_last>{}, "");
+static_assert( std::is_trivially_copy_assignable<date::weekday_last>{}, "");
+static_assert( std::is_trivially_move_constructible<date::weekday_last>{}, "");
+static_assert( std::is_trivially_move_assignable<date::weekday_last>{}, "");
+
+static_assert(std::is_nothrow_constructible<date::weekday_last, date::weekday>{}, "");
+static_assert(!std::is_convertible<date::weekday, date::weekday_last>{}, "");
+
+int
+main()
+{
+    using namespace date;
+
+    constexpr weekday_last wdl = sun[last];
+    static_assert(wdl.weekday() == sun, "");
+    static_assert(wdl.ok(), "");
+    static_assert(wdl == weekday_last{sun}, "");
+    static_assert(wdl != weekday_last{mon}, "");
+    std::ostringstream os;
+    os << wdl;
+    assert(os.str() == "Sun[last]");
+}
diff --git a/third_party/date-3.0.1/test/date_test/weekday_lessthan.fail.cpp b/third_party/date-3.0.1/test/date_test/weekday_lessthan.fail.cpp
new file mode 100644
index 00000000..a1fbc284
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/weekday_lessthan.fail.cpp
@@ -0,0 +1,32 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// weekday < weekday not allowed
+
+#include "date.h"
+
+int
+main()
+{
+    using namespace date;
+    auto b = sun < mon;
+}
diff --git a/third_party/date-3.0.1/test/date_test/weekday_sum.fail.cpp b/third_party/date-3.0.1/test/date_test/weekday_sum.fail.cpp
new file mode 100644
index 00000000..f4290511
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/weekday_sum.fail.cpp
@@ -0,0 +1,32 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// weekday + weekday not allowed
+
+#include "date.h"
+
+int
+main()
+{
+    using namespace date;
+    auto b = sun + mon;
+}
diff --git a/third_party/date-3.0.1/test/date_test/year.pass.cpp b/third_party/date-3.0.1/test/date_test/year.pass.cpp
new file mode 100644
index 00000000..585a2456
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/year.pass.cpp
@@ -0,0 +1,146 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// class year
+// {
+// public:
+//     explicit constexpr year(int y) noexcept;
+//
+//     year& operator++()    noexcept;
+//     year  operator++(int) noexcept;
+//     year& operator--()    noexcept;
+//     year  operator--(int) noexcept;
+//
+//     year& operator+=(const years& y) noexcept;
+//     year& operator-=(const years& y) noexcept;
+//
+//     constexpr bool is_leap() const noexcept;
+//
+//     constexpr explicit operator int() const noexcept;
+//     constexpr bool ok() const noexcept;
+//
+//     static constexpr year min() noexcept;
+//     static constexpr year max() noexcept;
+// };
+
+// constexpr bool operator==(const year& x, const year& y) noexcept;
+// constexpr bool operator!=(const year& x, const year& y) noexcept;
+// constexpr bool operator< (const year& x, const year& y) noexcept;
+// constexpr bool operator> (const year& x, const year& y) noexcept;
+// constexpr bool operator<=(const year& x, const year& y) noexcept;
+// constexpr bool operator>=(const year& x, const year& y) noexcept;
+
+// constexpr year  operator+(const year&  x, const years& y) noexcept;
+// constexpr year  operator+(const years& x, const year&  y) noexcept;
+// constexpr year  operator-(const year&  x, const years& y) noexcept;
+// constexpr years operator-(const year&  x, const year&  y) noexcept;
+
+// constexpr year operator "" _y(unsigned long long y) noexcept;
+// std::ostream& operator<<(std::ostream& os, const year& y);
+
+#include "date.h"
+
+#include <cassert>
+#include <sstream>
+#include <type_traits>
+
+static_assert( std::is_trivially_destructible<date::year>{}, "");
+static_assert( std::is_default_constructible<date::year>{}, "");
+static_assert( std::is_trivially_copy_constructible<date::year>{}, "");
+static_assert( std::is_trivially_copy_assignable<date::year>{}, "");
+static_assert( std::is_trivially_move_constructible<date::year>{}, "");
+static_assert( std::is_trivially_move_assignable<date::year>{}, "");
+
+static_assert( std::is_nothrow_constructible<date::year, int>{}, "");
+static_assert(!std::is_convertible<int, date::year>{}, "");
+static_assert( std::is_nothrow_constructible<int, date::year>{}, "");
+static_assert(!std::is_convertible<date::year, int>{}, "");
+static_assert(static_cast<int>(date::year{-1}) == -1, "");
+
+template <class Rep0, class Rep, class Period>
+constexpr
+inline
+std::chrono::duration<Rep0, Period>
+as(std::chrono::duration<Rep, Period> d)
+{
+   return d;
+}
+
+int
+main()
+{
+    using namespace date;
+    using namespace std::chrono;
+
+    static_assert(year{2015} == 2015_y, "");
+    static_assert(year{2015} != 2016_y, "");
+    static_assert(year{2015} < 2016_y, "");
+    static_assert(year{2016} > 2015_y, "");
+    static_assert(year{2015} <= 2015_y, "");
+    static_assert(year{2016} >= 2015_y, "");
+
+    static_assert(!year{2015}.is_leap(), "");
+    static_assert( year{2016}.is_leap(), "");
+
+    static_assert(year::min().ok(), "");
+    static_assert(year{2015}.ok(), "");
+    static_assert(year{2016}.ok(), "");
+    static_assert(year::max().ok(), "");
+
+#if __cplusplus >= 201402
+    using std::int64_t;
+    static_assert(sys_days(year::min()/jan/1)  - sys_days(1970_y/jan/1)
+        >= as<int64_t>(days::min()), "");
+    static_assert(sys_days(year::min()/jan/1)  - sys_days(1970_y/jan/1)
+        >= as<int64_t>(hours::min()), "");
+    static_assert(sys_days(year::min()/jan/1)  - sys_days(1970_y/jan/1)
+        >= as<int64_t>(minutes::min()), "");
+    static_assert(sys_days(year::min()/jan/1)  - sys_days(1970_y/jan/1)
+        >= as<int64_t>(seconds::min()), "");
+    static_assert(sys_days(year::min()/jan/1)  - sys_days(1970_y/jan/1)
+        >= as<int64_t>(milliseconds::min()), "");
+    static_assert(sys_days(year::min()/jan/1)  - sys_days(1970_y/jan/1)
+        >= as<int64_t>(microseconds::min()), "");
+    static_assert(sys_days(year::max()/dec/31) - sys_days(1970_y/jan/1)
+        <= as<int64_t>(microseconds::max()), "");
+    static_assert(sys_days(year::max()/dec/31) - sys_days(1970_y/jan/1)
+        <= as<int64_t>(milliseconds::max()), "");
+    static_assert(sys_days(year::max()/dec/31) - sys_days(1970_y/jan/1)
+        <= as<int64_t>(seconds::max()), "");
+    static_assert(sys_days(year::max()/dec/31) - sys_days(1970_y/jan/1)
+        <= as<int64_t>(minutes::max()), "");
+    static_assert(sys_days(year::max()/dec/31) - sys_days(1970_y/jan/1)
+        <= as<int64_t>(hours::max()), "");
+    static_assert(sys_days(year::max()/dec/31) - sys_days(1970_y/jan/1)
+        <= as<int64_t>(days::max()), "");
+#endif
+
+    static_assert(2015_y - 2010_y == years{5}, "");
+    static_assert(2015_y - years{5} == 2010_y, "");
+    static_assert(2015_y == years{5} + 2010_y, "");
+    static_assert(2015_y == 2010_y + years{5}, "");
+
+    auto y = 2015_y;
+    std::ostringstream os;
+    os << y;
+    assert(os.str() == "2015");
+}
diff --git a/third_party/date-3.0.1/test/date_test/year_month.pass.cpp b/third_party/date-3.0.1/test/date_test/year_month.pass.cpp
new file mode 100644
index 00000000..eec28a9f
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/year_month.pass.cpp
@@ -0,0 +1,227 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// class year_month
+// {
+// public:
+//     constexpr year_month(const date::year& y, const date::month& m) noexcept;
+//
+//     constexpr date::year  year()  const noexcept;
+//     constexpr date::month month() const noexcept;
+//
+//     year_month& operator+=(const months& dm) noexcept;
+//     year_month& operator-=(const months& dm) noexcept;
+//     year_month& operator+=(const years& dy) noexcept;
+//     year_month& operator-=(const years& dy) noexcept;
+//
+//     constexpr bool ok() const noexcept;
+// };
+
+// constexpr bool operator==(const year_month& x, const year_month& y) noexcept;
+// constexpr bool operator!=(const year_month& x, const year_month& y) noexcept;
+// constexpr bool operator< (const year_month& x, const year_month& y) noexcept;
+// constexpr bool operator> (const year_month& x, const year_month& y) noexcept;
+// constexpr bool operator<=(const year_month& x, const year_month& y) noexcept;
+// constexpr bool operator>=(const year_month& x, const year_month& y) noexcept;
+
+// constexpr year_month operator+(const year_month& ym, const months& dm) noexcept;
+// constexpr year_month operator+(const months& dm, const year_month& ym) noexcept;
+// constexpr year_month operator-(const year_month& ym, const months& dm) noexcept;
+
+// constexpr months operator-(const year_month& x, const year_month& y) noexcept;
+// constexpr year_month operator+(const year_month& ym, const years& dy) noexcept;
+// constexpr year_month operator+(const years& dy, const year_month& ym) noexcept;
+// constexpr year_month operator-(const year_month& ym, const years& dy) noexcept;
+
+// std::ostream& operator<<(std::ostream& os, const year_month& ym);
+
+#include "date.h"
+
+#include <cassert>
+#include <sstream>
+#include <type_traits>
+
+static_assert( std::is_trivially_destructible<date::year_month>{}, "");
+static_assert( std::is_default_constructible<date::year_month>{}, "");
+static_assert( std::is_trivially_copy_constructible<date::year_month>{}, "");
+static_assert( std::is_trivially_copy_assignable<date::year_month>{}, "");
+static_assert( std::is_trivially_move_constructible<date::year_month>{}, "");
+static_assert( std::is_trivially_move_assignable<date::year_month>{}, "");
+
+static_assert(std::is_nothrow_constructible<date::year_month, date::year,
+                                                              date::month>{}, "");
+
+void
+test_arithmetic()
+{
+    using namespace date;
+    using namespace std::chrono;
+
+    for (int y1 = 2010; y1 <= 2015; ++y1)
+    {
+        for (int y2 = 2010; y2 <= 2015; ++y2)
+        {
+            for (unsigned m1 = 1; m1 <= 12; ++m1)
+            {
+                for (unsigned m2 = 1; m2 <= 12; ++m2)
+                {
+                    year_month ym1{year{y1}, month{m1}};
+                    year_month ym2 = {year{y2}, month{m2}};
+                    months dm = ym1 - ym2;
+                    assert((dm < months{0}) == (ym1 < ym2));
+                    assert((dm == months{0}) == (ym1 == ym2));
+                    assert((dm > months{0}) == (ym1 > ym2));
+                    assert(dm + ym2 == ym1);
+                    assert(ym2 + dm == ym1);
+                    assert(ym1 - dm == ym2);
+                    years dy{y1-y2};
+                    assert((ym1 + dy == year_month{ym1.year() + dy, ym1.month()}));
+                    assert((dy + ym1 == year_month{ym1.year() + dy, ym1.month()}));
+                    assert((ym1 - dy == year_month{ym1.year() - dy, ym1.month()}));
+                    assert((year_month{ym2} += dm) == ym1);
+                    assert((year_month{ym1} -= dm) == ym2);
+                    assert(((year_month{ym1} += dy) ==
+                        year_month{ym1.year() + dy, ym1.month()}));
+                    assert(((year_month{ym1} -= dy) ==
+                        year_month{ym1.year() - dy, ym1.month()}));
+                }
+            }
+        }
+    }
+}
+
+
+void test_arithemtic_not_ok()
+{
+  using namespace date;
+  using namespace std::chrono;
+
+  year_month ym{2018_y, month{14}};
+
+  {
+    year_month ym2{2019_y, month{2}};
+    assert(ym + months{0} == ym2);
+    assert(ym - months{0} == ym2);
+    assert(ym - ym2 == months{0});
+    assert(ym2 - ym == months{0});
+   
+    auto ymc = ym;
+    ymc += months{0};
+    assert(ymc.ok());
+    assert(ymc == ym2);
+  }
+
+  {
+    year_month ym2{2019_y, month{6}};
+    assert(ym + months{4} == ym2);
+    assert(ym2 - ym == months{4});
+    assert(ym - ym2 == -months{4});
+
+    auto ymc = ym;
+    ymc += months{4};
+    assert(ymc.ok());
+    assert(ymc == ym2);
+  }
+
+  {
+    year_month ym2{2018_y, month{10}};
+    assert(ym - months{4} == ym2);
+    assert(ym2 - ym == -months{4});
+    assert(ym - ym2 == months{4});
+
+    auto ymc = ym;
+    ymc -= months{4};
+    assert(ymc.ok());
+    assert(ymc == ym2);
+  }
+
+
+  {
+    year_month ym2{2020_y, month{6}};
+    assert(ym + months{16} == ym2);
+    assert(ym2 - ym == months{16});
+    assert(ym - ym2 == -months{16});
+
+    auto ymc = ym;
+    ymc += months{16};
+    assert(ymc.ok());
+    assert(ymc == ym2);
+  }
+
+  {
+    year_month ym2{2017_y, month{10}};
+    assert(ym - months{16} == ym2);
+    assert(ym2 - ym == -months{16});
+    assert(ym - ym2 == months(16));
+
+    auto ymc = ym;
+    ymc -= months{16};
+    assert(ymc.ok());
+    assert(ymc == ym2);
+  }
+
+  {
+    year_month ym2{2018_y, month{25}};
+    assert(ym2 - ym == months{11});
+    assert(ym - ym2 == -months{11});
+  }
+
+  {
+    year_month ym2{2019_y, month{25}};
+    assert(ym2 - ym == months{23});
+    assert(ym - ym2 == -months{23});
+  }
+
+}
+
+int
+main()
+{
+    using namespace date;
+
+    constexpr year_month ym1 = {2015_y, jun};
+    static_assert(ym1.year() == year{2015}, "");
+    static_assert(ym1.month() == jun, "");
+    static_assert(ym1.ok(), "");
+
+    constexpr year_month ym2 = {2016_y, may};
+    static_assert(ym2.year() == year{2016}, "");
+    static_assert(ym2.month() == may, "");
+    static_assert(ym2.ok(), "");
+
+    static_assert(ym1 == ym1, "");
+    static_assert(ym1 != ym2, "");
+    static_assert(ym1 < ym2, "");
+    static_assert(ym1 <= ym2, "");
+    static_assert(ym2 > ym1, "");
+    static_assert(ym2 >= ym2, "");
+
+    static_assert(ym2 - ym1 == months{11}, "");
+    static_assert(ym1 - ym2 == -months{11}, "");
+
+    test_arithmetic();
+    test_arithemtic_not_ok();
+
+    std::ostringstream os;
+    os << ym1;
+    assert(os.str() == "2015/Jun");
+}
diff --git a/third_party/date-3.0.1/test/date_test/year_month_day.pass.cpp b/third_party/date-3.0.1/test/date_test/year_month_day.pass.cpp
new file mode 100644
index 00000000..91668888
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/year_month_day.pass.cpp
@@ -0,0 +1,244 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// class year_month_day
+// {
+// public:
+//     constexpr year_month_day(const date::year& y, const date::month& m,
+//                                const date::day& d) noexcept;
+//     constexpr year_month_day(const year_month_day_last& ymdl) noexcept;
+//     constexpr year_month_day(const sys_days& dp) noexcept;
+//
+//     year_month_day& operator+=(const months& m) noexcept;
+//     year_month_day& operator-=(const months& m) noexcept;
+//     year_month_day& operator+=(const years& y)  noexcept;
+//     year_month_day& operator-=(const years& y)  noexcept;
+//
+//     constexpr date::year  year()  const noexcept;
+//     constexpr date::month month() const noexcept;
+//     constexpr date::day   day()   const noexcept;
+//
+//     constexpr operator sys_days() const noexcept;
+//     constexpr bool ok() const noexcept;
+// };
+
+// constexpr bool operator==(const year_month_day& x, const year_month_day& y) noexcept;
+// constexpr bool operator!=(const year_month_day& x, const year_month_day& y) noexcept;
+// constexpr bool operator< (const year_month_day& x, const year_month_day& y) noexcept;
+// constexpr bool operator> (const year_month_day& x, const year_month_day& y) noexcept;
+// constexpr bool operator<=(const year_month_day& x, const year_month_day& y) noexcept;
+// constexpr bool operator>=(const year_month_day& x, const year_month_day& y) noexcept;
+
+// constexpr year_month_day operator+(const year_month_day& ymd, const months& dm) noexcept;
+// constexpr year_month_day operator+(const months& dm, const year_month_day& ymd) noexcept;
+// constexpr year_month_day operator-(const year_month_day& ymd, const months& dm) noexcept;
+// constexpr year_month_day operator+(const year_month_day& ymd, const years& dy)  noexcept;
+// constexpr year_month_day operator+(const years& dy, const year_month_day& ymd)  noexcept;
+// constexpr year_month_day operator-(const year_month_day& ymd, const years& dy)  noexcept;
+
+// std::ostream& operator<<(std::ostream& os, const year_month_day& ymd);
+
+#include "date.h"
+
+#include <cassert>
+#include <sstream>
+#include <type_traits>
+
+static_assert( std::is_trivially_destructible<date::year_month_day>{}, "");
+static_assert( std::is_default_constructible<date::year_month_day>{}, "");
+static_assert( std::is_trivially_copy_constructible<date::year_month_day>{}, "");
+static_assert( std::is_trivially_copy_assignable<date::year_month_day>{}, "");
+static_assert( std::is_trivially_move_constructible<date::year_month_day>{}, "");
+static_assert( std::is_trivially_move_assignable<date::year_month_day>{}, "");
+
+static_assert(std::is_nothrow_constructible<date::year_month_day, date::year,
+                                                                  date::month,
+                                                                  date::day>{}, "");
+static_assert(std::is_nothrow_constructible<date::year_month_day,
+                                            date::year_month_day_last>{}, "");
+static_assert(std::is_convertible<date::year_month_day_last, date::year_month_day>{}, "");
+static_assert(std::is_nothrow_constructible<date::year_month_day, date::sys_days>{}, "");
+static_assert(std::is_convertible<date::sys_days, date::year_month_day>{}, "");
+static_assert(std::is_nothrow_constructible<date::sys_days, date::year_month_day>{}, "");
+static_assert(std::is_convertible<date::year_month_day, date::sys_days>{}, "");
+
+void
+test_arithmetic()
+{
+    using namespace date;
+
+    for (int y1 = 2010; y1 <= 2015; ++y1)
+    {
+        for (unsigned m1 = 1; m1 <= 12; ++m1)
+        {
+            year_month_day ymd1{year{y1}, month{m1}, 9_d};
+            year_month_day ymd2 = ymd1 + months(24);
+            assert((ymd2 == year_month_day{year{y1+2}, ymd1.month(), ymd1.day()}));
+            ymd2 = ymd1 - months(24);
+            assert((ymd2 == year_month_day{year{y1-2}, ymd1.month(), ymd1.day()}));
+            for (int m2 = -24; m2 <= 24; ++m2)
+            {
+                months m{m2};
+                year_month_day ymd3 = ymd1 + m;
+                months dm = year_month{ymd3.year(), ymd3.month()} -
+                            year_month{ymd2.year(), ymd2.month()};
+                assert(dm == m + years{2});
+                assert(ymd3 - m == ymd1);
+                assert(ymd3 + -m == ymd1);
+                assert(-m + ymd3 == ymd1);
+                assert((year_month_day{ymd1} += m) == ymd3);
+                assert((year_month_day{ymd3} -= m) == ymd1);
+            }
+            for (int y2 = -2; y2 <= 5; ++y2)
+            {
+                years y{y2};
+                year_month_day ymd3 = ymd1 + y;
+                years dy = floor<years>(year_month{ymd3.year(), ymd3.month()} -
+                                        year_month{ymd2.year(), ymd2.month()});
+                assert(dy == y + years{2});
+                assert(ymd3 - y == ymd1);
+                assert(ymd3 + -y == ymd1);
+                assert(-y + ymd3 == ymd1);
+                assert((year_month_day{ymd1} += y) == ymd3);
+                assert((year_month_day{ymd3} -= y) == ymd1);
+            }
+        }
+    }
+}
+
+void
+test_day_point_conversion()
+{
+    using namespace date;
+    year y   = year{-1000};
+    year end =       3000_y;
+    sys_days prev_dp = sys_days(year_month_day{y, jan, 1_d}) - days{1};
+    weekday   prev_wd = weekday{prev_dp};
+    for (; y <= end; ++y)
+    {
+        month m = jan;
+        do
+        {
+            day last_day = year_month_day_last{y, month_day_last{m}}.day();
+            for (day d = 1_d; d <= last_day; ++d)
+            {
+                year_month_day ymd = {y, m, d};
+                assert(ymd.ok());
+                sys_days dp = ymd;
+                assert(dp == prev_dp + days{1});
+                year_month_day ymd2 = dp;
+                assert(ymd2 == ymd);
+                weekday wd = dp;
+                assert(wd.ok());
+                assert(wd == prev_wd + days{1});
+                prev_wd = wd;
+                prev_dp = dp;
+            }
+        } while (++m != jan);
+    }
+}
+
+int
+main()
+{
+    using namespace date;
+
+    constexpr year_month_day ymd1 = {2015_y, aug, 9_d};
+#if __cplusplus >= 201402
+    static_assert(ymd1.ok(), "");
+#endif
+    static_assert(ymd1.year() == 2015_y, "");
+    static_assert(ymd1.month() == aug, "");
+    static_assert(ymd1.day() == 9_d, "");
+
+#if __cplusplus >= 201402
+    constexpr sys_days dp = ymd1;
+    static_assert(dp.time_since_epoch() == days{16656}, "");
+    constexpr year_month_day ymd2 = dp;
+    static_assert(ymd1 == ymd2, "");
+#endif
+
+    constexpr year_month_day ymd3 = {1969_y, dec, 31_d};
+#if __cplusplus >= 201402
+    static_assert(ymd3.ok(), "");
+#endif
+    static_assert(ymd3.year() == 1969_y, "");
+    static_assert(ymd3.month() == dec, "");
+    static_assert(ymd3.day() == 31_d, "");
+
+#if __cplusplus >= 201402
+    constexpr sys_days dp3 = ymd3;
+    static_assert(dp3.time_since_epoch() == days{-1}, "");
+    constexpr year_month_day ymd4 = dp3;
+    static_assert(ymd3 == ymd4, "");
+#endif
+
+    static_assert(ymd1 != ymd3, "");
+    static_assert(ymd1 > ymd3, "");
+    static_assert(ymd3 < ymd1, "");
+    static_assert(ymd1 >= ymd1, "");
+    static_assert(ymd3 <= ymd1, "");
+
+    test_arithmetic();
+    test_day_point_conversion();
+
+    std::ostringstream os;
+    os << ymd1;
+    assert(os.str() == "2015-08-09");
+
+#if __cplusplus >= 201402
+    static_assert( (2000_y/feb/29).ok(), "");
+    static_assert(!(2000_y/feb/30).ok(), "");
+    static_assert( (2100_y/feb/28).ok(), "");
+    static_assert(!(2100_y/feb/29).ok(), "");
+
+    static_assert(sys_days(2100_y/feb/28) + days{1} == sys_days(2100_y/mar/1), "");
+    static_assert(sys_days(2000_y/mar/1) - sys_days(2000_y/feb/28) == days{2}, "");
+    static_assert(sys_days(2100_y/mar/1) - sys_days(2100_y/feb/28) == days{1}, "");
+
+    static_assert(jan/31/2015 == jan/last/2015, "");
+    static_assert(feb/28/2015 == feb/last/2015, "");
+    static_assert(mar/31/2015 == mar/last/2015, "");
+    static_assert(apr/30/2015 == apr/last/2015, "");
+    static_assert(may/31/2015 == may/last/2015, "");
+    static_assert(jun/30/2015 == jun/last/2015, "");
+    static_assert(jul/31/2015 == jul/last/2015, "");
+    static_assert(aug/31/2015 == aug/last/2015, "");
+    static_assert(sep/30/2015 == sep/last/2015, "");
+    static_assert(oct/31/2015 == oct/last/2015, "");
+    static_assert(nov/30/2015 == nov/last/2015, "");
+    static_assert(dec/31/2015 == dec/last/2015, "");
+
+    static_assert(jan/31/2016 == jan/last/2016, "");
+    static_assert(feb/29/2016 == feb/last/2016, "");
+    static_assert(mar/31/2016 == mar/last/2016, "");
+    static_assert(apr/30/2016 == apr/last/2016, "");
+    static_assert(may/31/2016 == may/last/2016, "");
+    static_assert(jun/30/2016 == jun/last/2016, "");
+    static_assert(jul/31/2016 == jul/last/2016, "");
+    static_assert(aug/31/2016 == aug/last/2016, "");
+    static_assert(sep/30/2016 == sep/last/2016, "");
+    static_assert(oct/31/2016 == oct/last/2016, "");
+    static_assert(nov/30/2016 == nov/last/2016, "");
+    static_assert(dec/31/2016 == dec/last/2016, "");
+#endif
+}
diff --git a/third_party/date-3.0.1/test/date_test/year_month_day_last.pass.cpp b/third_party/date-3.0.1/test/date_test/year_month_day_last.pass.cpp
new file mode 100644
index 00000000..41f1858e
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/year_month_day_last.pass.cpp
@@ -0,0 +1,177 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// class year_month_day_last
+// {
+// public:
+//     constexpr year_month_day_last(const date::year& y,
+//                                   const date::month_day_last& mdl) noexcept;
+//
+//     year_month_day_last& operator+=(const months& m) noexcept;
+//     year_month_day_last& operator-=(const months& m) noexcept;
+//     year_month_day_last& operator+=(const years& y)  noexcept;
+//     year_month_day_last& operator-=(const years& y)  noexcept;
+//
+//     constexpr date::year           year()           const noexcept;
+//     constexpr date::month          month()          const noexcept;
+//     constexpr date::month_day_last month_day_last() const noexcept;
+//     constexpr date::day            day()            const noexcept;
+//
+//     constexpr operator sys_days() const noexcept;
+//     constexpr bool ok() const noexcept;
+// };
+
+// constexpr
+//     bool operator==(const year_month_day_last& x, const year_month_day_last& y) noexcept;
+// constexpr
+//     bool operator!=(const year_month_day_last& x, const year_month_day_last& y) noexcept;
+// constexpr
+//     bool operator< (const year_month_day_last& x, const year_month_day_last& y) noexcept;
+// constexpr
+//     bool operator> (const year_month_day_last& x, const year_month_day_last& y) noexcept;
+// constexpr
+//     bool operator<=(const year_month_day_last& x, const year_month_day_last& y) noexcept;
+// constexpr
+//     bool operator>=(const year_month_day_last& x, const year_month_day_last& y) noexcept;
+
+// constexpr
+// year_month_day_last
+// operator+(const year_month_day_last& ymdl, const months& dm) noexcept;
+//
+// constexpr
+// year_month_day_last
+// operator+(const months& dm, const year_month_day_last& ymdl) noexcept;
+//
+// constexpr
+// year_month_day_last
+// operator+(const year_month_day_last& ymdl, const years& dy) noexcept;
+//
+// constexpr
+// year_month_day_last
+// operator+(const years& dy, const year_month_day_last& ymdl) noexcept;
+//
+// constexpr
+// year_month_day_last
+// operator-(const year_month_day_last& ymdl, const months& dm) noexcept;
+//
+// constexpr
+// year_month_day_last
+// operator-(const year_month_day_last& ymdl, const years& dy) noexcept;
+
+// std::ostream& operator<<(std::ostream& os, const year_month_day_last& ymdl);
+
+#include "date.h"
+
+#include <cassert>
+#include <sstream>
+#include <type_traits>
+
+static_assert( std::is_trivially_destructible<date::year_month_day_last>{}, "");
+static_assert(!std::is_default_constructible<date::year_month_day_last>{}, "");
+static_assert( std::is_trivially_copy_constructible<date::year_month_day_last>{}, "");
+static_assert( std::is_trivially_copy_assignable<date::year_month_day_last>{}, "");
+static_assert( std::is_trivially_move_constructible<date::year_month_day_last>{}, "");
+static_assert( std::is_trivially_move_assignable<date::year_month_day_last>{}, "");
+
+static_assert(std::is_nothrow_constructible<date::year_month_day_last,
+                                                date::year, date::month_day_last>{}, "");
+static_assert(std::is_nothrow_constructible<date::sys_days,
+                                                date::year_month_day_last>{}, "");
+static_assert(std::is_convertible<date::year_month_day_last, date::sys_days>{}, "");
+
+void
+test_arithmetic()
+{
+    using namespace date;
+
+    for (int y1 = 2010; y1 <= 2015; ++y1)
+    {
+        for (int m1 = 1; m1 <= 12; ++m1)
+        {
+            auto ymd1 = last/m1/y1;;
+            auto ymd2 = ymd1 + months(24);
+            assert(ymd2 == last/m1/(y1+2));
+            ymd2 = ymd1 - months(24);
+            assert(ymd2 == last/m1/(y1-2));
+            for (int m2 = -24; m2 <= 24; ++m2)
+            {
+                months m{m2};
+                auto ymd3 = ymd1 + m;
+                months dm = year_month{ymd3.year(), ymd3.month()} -
+                            year_month{ymd2.year(), ymd2.month()};
+                assert(dm == m + years{2});
+                assert(ymd3 - m == ymd1);
+                assert(ymd3 + -m == ymd1);
+                assert(-m + ymd3 == ymd1);
+                assert((year_month_day_last{ymd1} += m) == ymd3);
+                assert((year_month_day_last{ymd3} -= m) == ymd1);
+            }
+            for (int y2 = -2; y2 <= 5; ++y2)
+            {
+                years y{y2};
+                auto ymd3 = ymd1 + y;
+                years dy = floor<years>(year_month{ymd3.year(), ymd3.month()} -
+                                        year_month{ymd2.year(), ymd2.month()});
+                assert(dy == y + years{2});
+                assert(ymd3 - y == ymd1);
+                assert(ymd3 + -y == ymd1);
+                assert(-y + ymd3 == ymd1);
+                assert((year_month_day_last{ymd1} += y) == ymd3);
+                assert((year_month_day_last{ymd3} -= y) == ymd1);
+            }
+        }
+    }
+}
+
+int
+main()
+{
+    using namespace date;
+
+    constexpr year_month_day_last ymdl1 = {2015_y, month_day_last{aug}};
+    static_assert(ymdl1.ok(), "");
+    static_assert(ymdl1.year() == 2015_y, "");
+    static_assert(ymdl1.month() == aug, "");
+    static_assert(ymdl1.month_day_last() == month_day_last{aug}, "");
+#if __cplusplus >= 201402
+    static_assert(ymdl1.day() == 31_d, "");
+    constexpr sys_days dp = ymdl1;
+    constexpr year_month_day ymd = dp;
+    static_assert(ymd == 2015_y/aug/31, "");
+#endif
+
+    constexpr year_month_day_last ymdl2 = {2015_y, month_day_last{sep}};
+
+    static_assert(ymdl1 == ymdl1, "");
+    static_assert(ymdl1 != ymdl2, "");
+    static_assert(ymdl1 < ymdl2, "");
+    static_assert(ymdl2 > ymdl1, "");
+    static_assert(ymdl1 <= ymdl1, "");
+    static_assert(ymdl2 >= ymdl1, "");
+
+    test_arithmetic();
+
+    std::ostringstream os;
+    os << ymdl1;
+    assert(os.str() == "2015/Aug/last");
+
+}
diff --git a/third_party/date-3.0.1/test/date_test/year_month_day_m_year_month_day.fail.cpp b/third_party/date-3.0.1/test/date_test/year_month_day_m_year_month_day.fail.cpp
new file mode 100644
index 00000000..ceb2f9e9
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/year_month_day_m_year_month_day.fail.cpp
@@ -0,0 +1,33 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// year_month_day - year_month_day not allowed
+
+#include "date.h"
+
+int
+main()
+{
+    using namespace date;
+
+    auto x = year_month_day{2015_y, aug, 9_d} - year_month_day{2015_y, aug, 9_d};
+}
diff --git a/third_party/date-3.0.1/test/date_test/year_month_day_p_year_month_day.fail.cpp b/third_party/date-3.0.1/test/date_test/year_month_day_p_year_month_day.fail.cpp
new file mode 100644
index 00000000..11e589ff
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/year_month_day_p_year_month_day.fail.cpp
@@ -0,0 +1,33 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// year_month_day + year_month_day not allowed
+
+#include "date.h"
+
+int
+main()
+{
+    using namespace date;
+
+    auto x = year_month_day{2015_y, aug, 9_d} + year_month_day{2015_y, aug, 9_d};
+}
diff --git a/third_party/date-3.0.1/test/date_test/year_month_p_year_month.fail.cpp b/third_party/date-3.0.1/test/date_test/year_month_p_year_month.fail.cpp
new file mode 100644
index 00000000..00049f11
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/year_month_p_year_month.fail.cpp
@@ -0,0 +1,33 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// year_month + year_month not allowed
+
+#include "date.h"
+
+int
+main()
+{
+    using namespace date;
+
+    auto x = year_month{2015_y, jan} + year_month{2015_y, jan};
+}
diff --git a/third_party/date-3.0.1/test/date_test/year_month_weekday.pass.cpp b/third_party/date-3.0.1/test/date_test/year_month_weekday.pass.cpp
new file mode 100644
index 00000000..1a6ed0d3
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/year_month_weekday.pass.cpp
@@ -0,0 +1,178 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// class year_month_weekday
+// {
+// public:
+//     year_month_weekday() = default;
+//     constexpr year_month_weekday(const date::year& y, const date::month& m,
+//                                    const date::weekday_indexed& wdi) noexcept;
+//     constexpr year_month_weekday(const sys_days& dp) noexcept;
+//
+//     year_month_weekday& operator+=(const months& m) noexcept;
+//     year_month_weekday& operator-=(const months& m) noexcept;
+//     year_month_weekday& operator+=(const years& y)  noexcept;
+//     year_month_weekday& operator-=(const years& y)  noexcept;
+//
+//     constexpr date::year year() const noexcept;
+//     constexpr date::month month() const noexcept;
+//     constexpr date::weekday weekday() const noexcept;
+//     constexpr unsigned index() const noexcept;
+//     constexpr date::weekday_indexed weekday_indexed() const noexcept;
+//
+//     constexpr operator sys_days() const noexcept;
+//     constexpr bool ok() const noexcept;
+//
+// private:
+//     static constexpr year_month_weekday from_day_point(const sys_days& dp) noexcept;
+// };
+
+// constexpr
+//     bool operator==(const year_month_weekday& x, const year_month_weekday& y) noexcept;
+// constexpr
+//     bool operator!=(const year_month_weekday& x, const year_month_weekday& y) noexcept;
+
+// constexpr
+// year_month_weekday
+// operator+(const year_month_weekday& ymwd, const months& dm) noexcept;
+//
+// constexpr
+// year_month_weekday
+// operator+(const months& dm, const year_month_weekday& ymwd) noexcept;
+//
+// constexpr
+// year_month_weekday
+// operator+(const year_month_weekday& ymwd, const years& dy) noexcept;
+//
+// constexpr
+// year_month_weekday
+// operator+(const years& dy, const year_month_weekday& ymwd) noexcept;
+//
+// constexpr
+// year_month_weekday
+// operator-(const year_month_weekday& ymwd, const months& dm) noexcept;
+//
+// constexpr
+// year_month_weekday
+// operator-(const year_month_weekday& ymwd, const years& dy) noexcept;
+
+// std::ostream& operator<<(std::ostream& os, const year_month_weekday& ymwdi);
+
+#include "date.h"
+
+#include <cassert>
+#include <sstream>
+#include <type_traits>
+
+static_assert( std::is_trivially_destructible<date::year_month_weekday>{}, "");
+static_assert( std::is_default_constructible<date::year_month_weekday>{}, "");
+static_assert( std::is_trivially_copy_constructible<date::year_month_weekday>{}, "");
+static_assert( std::is_trivially_copy_assignable<date::year_month_weekday>{}, "");
+static_assert( std::is_trivially_move_constructible<date::year_month_weekday>{}, "");
+static_assert( std::is_trivially_move_assignable<date::year_month_weekday>{}, "");
+
+static_assert(std::is_nothrow_constructible<date::year_month_weekday,
+                                                date::year, date::month,
+                                                date::weekday_indexed>{}, "");
+static_assert(std::is_nothrow_constructible<date::year_month_weekday,
+                                                date::sys_days>{}, "");
+static_assert(std::is_convertible<date::sys_days, date::year_month_weekday>{}, "");
+static_assert(std::is_nothrow_constructible<date::sys_days,
+                                                date::year_month_weekday>{}, "");
+static_assert(std::is_convertible<date::year_month_weekday, date::sys_days>{}, "");
+
+void
+test_arithmetic()
+{
+    using namespace date;
+
+    for (int y1 = 2010; y1 <= 2015; ++y1)
+    {
+        for (int m1 = 1; m1 <= 12; ++m1)
+        {
+            auto ymd1 = mon[2]/m1/y1;;
+            auto ymd2 = ymd1 + months(24);
+            assert(ymd2 == mon[2]/m1/(y1+2));
+            ymd2 = ymd1 - months(24);
+            assert(ymd2 == mon[2]/m1/(y1-2));
+            for (int m2 = -24; m2 <= 24; ++m2)
+            {
+                months m{m2};
+                auto ymd3 = ymd1 + m;
+                months dm = year_month{ymd3.year(), ymd3.month()} -
+                            year_month{ymd2.year(), ymd2.month()};
+                assert(dm == m + years{2});
+                assert(ymd3 - m == ymd1);
+                assert(ymd3 + -m == ymd1);
+                assert(-m + ymd3 == ymd1);
+                assert((year_month_weekday{ymd1} += m) == ymd3);
+                assert((year_month_weekday{ymd3} -= m) == ymd1);
+            }
+            for (int y2 = -2; y2 <= 5; ++y2)
+            {
+                years y{y2};
+                auto ymd3 = ymd1 + y;
+                years dy = floor<years>(year_month{ymd3.year(), ymd3.month()} -
+                                        year_month{ymd2.year(), ymd2.month()});
+                assert(dy == y + years{2});
+                assert(ymd3 - y == ymd1);
+                assert(ymd3 + -y == ymd1);
+                assert(-y + ymd3 == ymd1);
+                assert((year_month_weekday{ymd1} += y) == ymd3);
+                assert((year_month_weekday{ymd3} -= y) == ymd1);
+            }
+        }
+    }
+}
+
+int
+main()
+{
+    using namespace date;
+
+    constexpr year_month_weekday ymdl1 = {2015_y, aug, weekday_indexed{fri, 2}};
+#if __cplusplus >= 201402
+    static_assert(ymdl1.ok(), "");
+#endif
+    static_assert(ymdl1.year() == 2015_y, "");
+    static_assert(ymdl1.month() == aug, "");
+    static_assert(ymdl1.weekday() == fri, "");
+    static_assert(ymdl1.index() == 2u, "");
+    static_assert(ymdl1.weekday_indexed() == fri[2], "");
+#if __cplusplus >= 201402
+    constexpr sys_days dp = ymdl1;
+    constexpr year_month_day ymd = dp;
+    static_assert(ymd == 2015_y/aug/14, "");
+#endif
+
+    constexpr year_month_weekday ymdl2 = sat[1]/aug/2015;
+
+    static_assert(ymdl1 == ymdl1, "");
+    static_assert(ymdl1 != ymdl2, "");
+
+    test_arithmetic();
+
+    std::ostringstream os;
+    os << ymdl1;
+    assert(os.str() == "2015/Aug/Fri[2]");
+
+}
diff --git a/third_party/date-3.0.1/test/date_test/year_month_weekday_last.pass.cpp b/third_party/date-3.0.1/test/date_test/year_month_weekday_last.pass.cpp
new file mode 100644
index 00000000..3abe1133
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/year_month_weekday_last.pass.cpp
@@ -0,0 +1,169 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// class year_month_weekday_last
+// {
+// public:
+//     constexpr year_month_weekday_last(const date::year& y, const date::month& m,
+//                                       const date::weekday_last& wdl) noexcept;
+//
+//     year_month_weekday_last& operator+=(const months& m) noexcept;
+//     year_month_weekday_last& operator-=(const months& m) noexcept;
+//     year_month_weekday_last& operator+=(const years& y) noexcept;
+//     year_month_weekday_last& operator-=(const years& y) noexcept;
+//
+//     constexpr date::year year() const noexcept;
+//     constexpr date::month month() const noexcept;
+//     constexpr date::weekday weekday() const noexcept;
+//     constexpr date::weekday_last weekday_last() const noexcept;
+//
+//     constexpr operator sys_days() const noexcept;
+//     constexpr bool ok() const noexcept;
+// };
+
+// constexpr
+// bool
+// operator==(const year_month_weekday_last& x, const year_month_weekday_last& y) noexcept;
+//
+// constexpr
+// bool
+// operator!=(const year_month_weekday_last& x, const year_month_weekday_last& y) noexcept;
+
+// constexpr
+// year_month_weekday_last
+// operator+(const year_month_weekday_last& ymwdl, const months& dm) noexcept;
+//
+// constexpr
+// year_month_weekday_last
+// operator+(const months& dm, const year_month_weekday_last& ymwdl) noexcept;
+//
+// constexpr
+// year_month_weekday_last
+// operator+(const year_month_weekday_last& ymwdl, const years& dy) noexcept;
+//
+// constexpr
+// year_month_weekday_last
+// operator+(const years& dy, const year_month_weekday_last& ymwdl) noexcept;
+//
+// constexpr
+// year_month_weekday_last
+// operator-(const year_month_weekday_last& ymwdl, const months& dm) noexcept;
+//
+// constexpr
+// year_month_weekday_last
+// operator-(const year_month_weekday_last& ymwdl, const years& dy) noexcept;
+
+// std::ostream& operator<<(std::ostream& os, const year_month_weekday_last& ymwdl);
+
+#include "date.h"
+
+#include <cassert>
+#include <sstream>
+#include <type_traits>
+
+static_assert( std::is_trivially_destructible<date::year_month_weekday_last>{}, "");
+static_assert(!std::is_default_constructible<date::year_month_weekday_last>{}, "");
+static_assert( std::is_trivially_copy_constructible<date::year_month_weekday_last>{}, "");
+static_assert( std::is_trivially_copy_assignable<date::year_month_weekday_last>{}, "");
+static_assert( std::is_trivially_move_constructible<date::year_month_weekday_last>{}, "");
+static_assert( std::is_trivially_move_assignable<date::year_month_weekday_last>{}, "");
+
+static_assert(std::is_nothrow_constructible<date::year_month_weekday_last,
+                                                date::year, date::month,
+                                                date::weekday_last>{}, "");
+static_assert(std::is_nothrow_constructible<date::sys_days,
+                                                date::year_month_weekday_last>{}, "");
+static_assert(std::is_convertible<date::year_month_weekday_last, date::sys_days>{}, "");
+
+void
+test_arithmetic()
+{
+    using namespace date;
+
+    for (int y1 = 2010; y1 <= 2015; ++y1)
+    {
+        for (int m1 = 1; m1 <= 12; ++m1)
+        {
+            auto ymd1 = mon[last]/m1/y1;;
+            auto ymd2 = ymd1 + months(24);
+            assert(ymd2 == mon[last]/m1/(y1+2));
+            ymd2 = ymd1 - months(24);
+            assert(ymd2 == mon[last]/m1/(y1-2));
+            for (int m2 = -24; m2 <= 24; ++m2)
+            {
+                months m{m2};
+                auto ymd3 = ymd1 + m;
+                months dm = year_month{ymd3.year(), ymd3.month()} -
+                            year_month{ymd2.year(), ymd2.month()};
+                assert(dm == m + years{2});
+                assert(ymd3 - m == ymd1);
+                assert(ymd3 + -m == ymd1);
+                assert(-m + ymd3 == ymd1);
+                assert((year_month_weekday_last{ymd1} += m) == ymd3);
+                assert((year_month_weekday_last{ymd3} -= m) == ymd1);
+            }
+            for (int y2 = -2; y2 <= 5; ++y2)
+            {
+                years y{y2};
+                auto ymd3 = ymd1 + y;
+                years dy = floor<years>(year_month{ymd3.year(), ymd3.month()} -
+                                        year_month{ymd2.year(), ymd2.month()});
+                assert(dy == y + years{2});
+                assert(ymd3 - y == ymd1);
+                assert(ymd3 + -y == ymd1);
+                assert(-y + ymd3 == ymd1);
+                assert((year_month_weekday_last{ymd1} += y) == ymd3);
+                assert((year_month_weekday_last{ymd3} -= y) == ymd1);
+            }
+        }
+    }
+}
+
+int
+main()
+{
+    using namespace date;
+
+    constexpr year_month_weekday_last ymdl1 = {2015_y, aug, weekday_last{fri}};
+    static_assert(ymdl1.ok(), "");
+    static_assert(ymdl1.year() == 2015_y, "");
+    static_assert(ymdl1.month() == aug, "");
+    static_assert(ymdl1.weekday() == fri, "");
+    static_assert(ymdl1.weekday_last() == fri[last], "");
+#if __cplusplus >= 201402
+    constexpr sys_days dp = ymdl1;
+    constexpr year_month_day ymd = dp;
+    static_assert(ymd == 2015_y/aug/28, "");
+#endif
+
+    constexpr year_month_weekday_last ymdl2 = sat[last]/aug/2015;
+
+    static_assert(ymdl1 == ymdl1, "");
+    static_assert(ymdl1 != ymdl2, "");
+
+    test_arithmetic();
+
+    std::ostringstream os;
+    os << ymdl1;
+    assert(os.str() == "2015/Aug/Fri[last]");
+
+}
diff --git a/third_party/date-3.0.1/test/date_test/year_p_year.fail.cpp b/third_party/date-3.0.1/test/date_test/year_p_year.fail.cpp
new file mode 100644
index 00000000..79e56b92
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/year_p_year.fail.cpp
@@ -0,0 +1,32 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// year + year not allowed
+
+#include "date.h"
+
+int
+main()
+{
+    using namespace date;
+    auto x = 2015_y + 2015_y;
+}
diff --git a/third_party/date-3.0.1/test/date_test/years_m_year.fail.cpp b/third_party/date-3.0.1/test/date_test/years_m_year.fail.cpp
new file mode 100644
index 00000000..b2c01cfd
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/years_m_year.fail.cpp
@@ -0,0 +1,32 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// years - year not allowed
+
+#include "date.h"
+
+int
+main()
+{
+    using namespace date;
+    auto x = years{3} - 2015_y;
+}
diff --git a/third_party/date-3.0.1/test/date_test/years_m_year_month.fail.cpp b/third_party/date-3.0.1/test/date_test/years_m_year_month.fail.cpp
new file mode 100644
index 00000000..c2cb96c2
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/years_m_year_month.fail.cpp
@@ -0,0 +1,33 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// years - year_month not allowed
+
+#include "date.h"
+
+int
+main()
+{
+    using namespace date;
+
+    auto x = years{1} - year_month{2015_y, jan};
+}
diff --git a/third_party/date-3.0.1/test/date_test/years_m_year_month_day.fail.cpp b/third_party/date-3.0.1/test/date_test/years_m_year_month_day.fail.cpp
new file mode 100644
index 00000000..beeb4f59
--- /dev/null
+++ b/third_party/date-3.0.1/test/date_test/years_m_year_month_day.fail.cpp
@@ -0,0 +1,33 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// years - year_month_day not allowed
+
+#include "date.h"
+
+int
+main()
+{
+    using namespace date;
+
+    auto x = 2015_y - year_month_day{2015_y, aug, 9_d};
+}
diff --git a/third_party/date-3.0.1/test/iso_week/last.pass.cpp b/third_party/date-3.0.1/test/iso_week/last.pass.cpp
new file mode 100644
index 00000000..dad8cbb7
--- /dev/null
+++ b/third_party/date-3.0.1/test/iso_week/last.pass.cpp
@@ -0,0 +1,34 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// constexpr struct last_spec {} last{};
+
+#include "iso_week.h"
+
+#include <type_traits>
+
+static_assert(std::is_same<decltype(iso_week::last), const iso_week::last_week>{}, "");
+
+int
+main()
+{
+}
diff --git a/third_party/date-3.0.1/test/iso_week/lastweek_weekday.pass.cpp b/third_party/date-3.0.1/test/iso_week/lastweek_weekday.pass.cpp
new file mode 100644
index 00000000..3ffbb252
--- /dev/null
+++ b/third_party/date-3.0.1/test/iso_week/lastweek_weekday.pass.cpp
@@ -0,0 +1,82 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// class lastweek_weekday
+// {
+//     iso_week::weekday wd_;  // exposition only
+//
+// public:
+//     explicit constexpr lastweek_weekday(const iso_week::weekday& wd) noexcept;
+//
+//     constexpr iso_week::weekday weekday() const noexcept;
+//
+//     constexpr bool ok() const noexcept;
+// };
+//
+// constexpr bool operator==(const lastweek_weekday& x, const lastweek_weekday& y) noexcept;
+// constexpr bool operator!=(const lastweek_weekday& x, const lastweek_weekday& y) noexcept;
+// constexpr bool operator< (const lastweek_weekday& x, const lastweek_weekday& y) noexcept;
+// constexpr bool operator> (const lastweek_weekday& x, const lastweek_weekday& y) noexcept;
+// constexpr bool operator<=(const lastweek_weekday& x, const lastweek_weekday& y) noexcept;
+// constexpr bool operator>=(const lastweek_weekday& x, const lastweek_weekday& y) noexcept;
+//
+// std::ostream& operator<<(std::ostream& os, const lastweek_weekday& md);
+
+#include "iso_week.h"
+
+#include <cassert>
+#include <sstream>
+#include <type_traits>
+
+static_assert( std::is_trivially_destructible<iso_week::lastweek_weekday>{}, "");
+static_assert(!std::is_default_constructible<iso_week::lastweek_weekday>{}, "");
+static_assert( std::is_trivially_copy_constructible<iso_week::lastweek_weekday>{}, "");
+static_assert( std::is_trivially_copy_assignable<iso_week::lastweek_weekday>{}, "");
+static_assert( std::is_trivially_move_constructible<iso_week::lastweek_weekday>{}, "");
+static_assert( std::is_trivially_move_assignable<iso_week::lastweek_weekday>{}, "");
+
+static_assert(std::is_trivially_copyable<iso_week::lastweek_weekday>{}, "");
+static_assert(std::is_standard_layout<iso_week::lastweek_weekday>{}, "");
+static_assert(std::is_literal_type<iso_week::lastweek_weekday>{}, "");
+
+static_assert( std::is_nothrow_constructible<iso_week::lastweek_weekday,
+                                                 iso_week::weekday>{}, "");
+static_assert(!std::is_convertible<iso_week::weekday, iso_week::lastweek_weekday>{}, "");
+
+int
+main()
+{
+    using namespace iso_week;
+
+    constexpr auto wn_wd = lastweek_weekday{tue};
+    static_assert(wn_wd.weekday() == tue, "");
+
+    static_assert(wn_wd.ok(), "");
+
+    static_assert(wn_wd == lastweek_weekday{tue}, "");
+    static_assert(!(wn_wd != lastweek_weekday{tue}), "");
+    static_assert(wn_wd < lastweek_weekday{wed}, "");
+
+    std::ostringstream os;
+    os << wn_wd;
+    assert(os.str() == "W last-Tue");
+}
diff --git a/third_party/date-3.0.1/test/iso_week/op_div_survey.pass.cpp b/third_party/date-3.0.1/test/iso_week/op_div_survey.pass.cpp
new file mode 100644
index 00000000..52e18868
--- /dev/null
+++ b/third_party/date-3.0.1/test/iso_week/op_div_survey.pass.cpp
@@ -0,0 +1,196 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+#include "iso_week.h"
+
+#include <type_traits>
+
+template <class I, class J, class K>
+constexpr
+auto
+test(I i, J j, K k) -> decltype(i/j/k)
+{
+    return i/j/k;
+}
+
+void
+test(...)
+{
+}
+
+int
+main()
+{
+    using std::is_same;
+    using namespace iso_week;
+
+    static_assert(is_same<decltype(test(   1,    1,    1)), int>{}, "");
+    static_assert(is_same<decltype(test(   1,    1,  mon)), void>{}, "");
+    static_assert(is_same<decltype(test(   1,    1,  1_w)), void>{}, "");
+    static_assert(is_same<decltype(test(   1,    1,  1_y)), void>{}, "");
+    static_assert(is_same<decltype(test(   1,    1, last)), void>{}, "");
+
+    static_assert(is_same<decltype(test(   1,  mon,    1)), void>{}, "");
+    static_assert(is_same<decltype(test(   1,  mon,  mon)), void>{}, "");
+    static_assert(is_same<decltype(test(   1,  mon,  1_w)), void>{}, "");
+    static_assert(is_same<decltype(test(   1,  mon,  1_y)), void>{}, "");
+    static_assert(is_same<decltype(test(   1,  mon, last)), void>{}, "");
+
+    static_assert(is_same<decltype(test(   1,  1_w,    1)), void>{}, "");
+    static_assert(is_same<decltype(test(   1,  1_w,  mon)), void>{}, "");
+    static_assert(is_same<decltype(test(   1,  1_w,  1_w)), void>{}, "");
+    static_assert(is_same<decltype(test(   1,  1_w,  1_y)), void>{}, "");
+    static_assert(is_same<decltype(test(   1,  1_w, last)), void>{}, "");
+
+    static_assert(is_same<decltype(test(   1,  1_y,    1)), void>{}, "");
+    static_assert(is_same<decltype(test(   1,  1_y,  mon)), void>{}, "");
+    static_assert(is_same<decltype(test(   1,  1_y,  1_w)), void>{}, "");
+    static_assert(is_same<decltype(test(   1,  1_y,  1_y)), void>{}, "");
+    static_assert(is_same<decltype(test(   1,  1_y, last)), void>{}, "");
+
+    static_assert(is_same<decltype(test(   1, last,    1)), void>{}, "");
+    static_assert(is_same<decltype(test(   1, last,  mon)), void>{}, "");
+    static_assert(is_same<decltype(test(   1, last,  1_w)), void>{}, "");
+    static_assert(is_same<decltype(test(   1, last,  1_y)), void>{}, "");
+    static_assert(is_same<decltype(test(   1, last, last)), void>{}, "");
+
+    static_assert(is_same<decltype(test( mon,    1,    1)), year_weeknum_weekday>{}, "");
+    static_assert(is_same<decltype(test( mon,    1,  mon)), void>{}, "");
+    static_assert(is_same<decltype(test( mon,    1,  1_w)), void>{}, "");
+    static_assert(is_same<decltype(test( mon,    1,  1_y)), year_weeknum_weekday>{}, "");
+    static_assert(is_same<decltype(test( mon,    1, last)), void>{}, "");
+
+    static_assert(is_same<decltype(test( mon,  mon,    1)), void>{}, "");
+    static_assert(is_same<decltype(test( mon,  mon,  mon)), void>{}, "");
+    static_assert(is_same<decltype(test( mon,  mon,  1_w)), void>{}, "");
+    static_assert(is_same<decltype(test( mon,  mon,  1_y)), void>{}, "");
+    static_assert(is_same<decltype(test( mon,  mon, last)), void>{}, "");
+
+    static_assert(is_same<decltype(test( mon,  1_w,    1)), year_weeknum_weekday>{}, "");
+    static_assert(is_same<decltype(test( mon,  1_w,  mon)), void>{}, "");
+    static_assert(is_same<decltype(test( mon,  1_w,  1_w)), void>{}, "");
+    static_assert(is_same<decltype(test( mon,  1_w,  1_y)), year_weeknum_weekday>{}, "");
+    static_assert(is_same<decltype(test( mon,  1_w, last)), void>{}, "");
+
+    static_assert(is_same<decltype(test( mon,  1_y,    1)), void>{}, "");
+    static_assert(is_same<decltype(test( mon,  1_y,  mon)), void>{}, "");
+    static_assert(is_same<decltype(test( mon,  1_y,  1_w)), void>{}, "");
+    static_assert(is_same<decltype(test( mon,  1_y,  1_y)), void>{}, "");
+    static_assert(is_same<decltype(test( mon,  1_y, last)), void>{}, "");
+
+    static_assert(is_same<decltype(test( mon, last,    1)), year_lastweek_weekday>{}, "");
+    static_assert(is_same<decltype(test( mon, last,  mon)), void>{}, "");
+    static_assert(is_same<decltype(test( mon, last,  1_w)), void>{}, "");
+    static_assert(is_same<decltype(test( mon, last,  1_y)), year_lastweek_weekday>{}, "");
+    static_assert(is_same<decltype(test( mon, last, last)), void>{}, "");
+
+    static_assert(is_same<decltype(test( 1_w,    1,    1)), year_weeknum_weekday>{}, "");
+    static_assert(is_same<decltype(test( 1_w,    1,  mon)), void>{}, "");
+    static_assert(is_same<decltype(test( 1_w,    1,  1_w)), void>{}, "");
+    static_assert(is_same<decltype(test( 1_w,    1,  1_y)), year_weeknum_weekday>{}, "");
+    static_assert(is_same<decltype(test( 1_w,    1, last)), void>{}, "");
+
+    static_assert(is_same<decltype(test( 1_w,  mon,    1)), year_weeknum_weekday>{}, "");
+    static_assert(is_same<decltype(test( 1_w,  mon,  mon)), void>{}, "");
+    static_assert(is_same<decltype(test( 1_w,  mon,  1_w)), void>{}, "");
+    static_assert(is_same<decltype(test( 1_w,  mon,  1_y)), year_weeknum_weekday>{}, "");
+    static_assert(is_same<decltype(test( 1_w,  mon, last)), void>{}, "");
+
+    static_assert(is_same<decltype(test( 1_w,  1_w,    1)), void>{}, "");
+    static_assert(is_same<decltype(test( 1_w,  1_w,  mon)), void>{}, "");
+    static_assert(is_same<decltype(test( 1_w,  1_w,  1_w)), void>{}, "");
+    static_assert(is_same<decltype(test( 1_w,  1_w,  1_y)), void>{}, "");
+    static_assert(is_same<decltype(test( 1_w,  1_w, last)), void>{}, "");
+
+    static_assert(is_same<decltype(test( 1_w,  1_y,    1)), void>{}, "");
+    static_assert(is_same<decltype(test( 1_w,  1_y,  mon)), void>{}, "");
+    static_assert(is_same<decltype(test( 1_w,  1_y,  1_w)), void>{}, "");
+    static_assert(is_same<decltype(test( 1_w,  1_y,  1_y)), void>{}, "");
+    static_assert(is_same<decltype(test( 1_w,  1_y, last)), void>{}, "");
+
+    static_assert(is_same<decltype(test( 1_w, last,    1)), void>{}, "");
+    static_assert(is_same<decltype(test( 1_w, last,  mon)), void>{}, "");
+    static_assert(is_same<decltype(test( 1_w, last,  1_w)), void>{}, "");
+    static_assert(is_same<decltype(test( 1_w, last,  1_y)), void>{}, "");
+    static_assert(is_same<decltype(test( 1_w, last, last)), void>{}, "");
+
+    static_assert(is_same<decltype(test( 1_y,    1,    1)), year_weeknum_weekday>{}, "");
+    static_assert(is_same<decltype(test( 1_y,    1,  mon)), year_weeknum_weekday>{}, "");
+    static_assert(is_same<decltype(test( 1_y,    1,  1_w)), void>{}, "");
+    static_assert(is_same<decltype(test( 1_y,    1,  1_y)), void>{}, "");
+    static_assert(is_same<decltype(test( 1_y,    1, last)), void>{}, "");
+
+    static_assert(is_same<decltype(test( 1_y,  mon,    1)), void>{}, "");
+    static_assert(is_same<decltype(test( 1_y,  mon,  mon)), void>{}, "");
+    static_assert(is_same<decltype(test( 1_y,  mon,  1_w)), void>{}, "");
+    static_assert(is_same<decltype(test( 1_y,  mon,  1_y)), void>{}, "");
+    static_assert(is_same<decltype(test( 1_y,  mon, last)), void>{}, "");
+
+    static_assert(is_same<decltype(test( 1_y,  1_w,    1)), year_weeknum_weekday>{}, "");
+    static_assert(is_same<decltype(test( 1_y,  1_w,  mon)), year_weeknum_weekday>{}, "");
+    static_assert(is_same<decltype(test( 1_y,  1_w,  1_w)), void>{}, "");
+    static_assert(is_same<decltype(test( 1_y,  1_w,  1_y)), void>{}, "");
+    static_assert(is_same<decltype(test( 1_y,  1_w, last)), void>{}, "");
+
+    static_assert(is_same<decltype(test( 1_y,  1_y,    1)), void>{}, "");
+    static_assert(is_same<decltype(test( 1_y,  1_y,  mon)), void>{}, "");
+    static_assert(is_same<decltype(test( 1_y,  1_y,  1_w)), void>{}, "");
+    static_assert(is_same<decltype(test( 1_y,  1_y,  1_y)), void>{}, "");
+    static_assert(is_same<decltype(test( 1_y,  1_y, last)), void>{}, "");
+
+    static_assert(is_same<decltype(test( 1_y, last,    1)), year_lastweek_weekday>{}, "");
+    static_assert(is_same<decltype(test( 1_y, last,  mon)), year_lastweek_weekday>{}, "");
+    static_assert(is_same<decltype(test( 1_y, last,  1_w)), void>{}, "");
+    static_assert(is_same<decltype(test( 1_y, last,  1_y)), void>{}, "");
+    static_assert(is_same<decltype(test( 1_y, last, last)), void>{}, "");
+
+    static_assert(is_same<decltype(test(last,    1,    1)), year_lastweek_weekday>{}, "");
+    static_assert(is_same<decltype(test(last,    1,  mon)), void>{}, "");
+    static_assert(is_same<decltype(test(last,    1,  1_w)), void>{}, "");
+    static_assert(is_same<decltype(test(last,    1,  1_y)), year_lastweek_weekday>{}, "");
+    static_assert(is_same<decltype(test(last,    1, last)), void>{}, "");
+
+    static_assert(is_same<decltype(test(last,  mon,    1)), year_lastweek_weekday>{}, "");
+    static_assert(is_same<decltype(test(last,  mon,  mon)), void>{}, "");
+    static_assert(is_same<decltype(test(last,  mon,  1_w)), void>{}, "");
+    static_assert(is_same<decltype(test(last,  mon,  1_y)), year_lastweek_weekday>{}, "");
+    static_assert(is_same<decltype(test(last,  mon, last)), void>{}, "");
+
+    static_assert(is_same<decltype(test(last,  1_w,    1)), void>{}, "");
+    static_assert(is_same<decltype(test(last,  1_w,  mon)), void>{}, "");
+    static_assert(is_same<decltype(test(last,  1_w,  1_w)), void>{}, "");
+    static_assert(is_same<decltype(test(last,  1_w,  1_y)), void>{}, "");
+    static_assert(is_same<decltype(test(last,  1_w, last)), void>{}, "");
+
+    static_assert(is_same<decltype(test(last,  1_y,    1)), void>{}, "");
+    static_assert(is_same<decltype(test(last,  1_y,  mon)), void>{}, "");
+    static_assert(is_same<decltype(test(last,  1_y,  1_w)), void>{}, "");
+    static_assert(is_same<decltype(test(last,  1_y,  1_y)), void>{}, "");
+    static_assert(is_same<decltype(test(last,  1_y, last)), void>{}, "");
+
+    static_assert(is_same<decltype(test(last, last,    1)), void>{}, "");
+    static_assert(is_same<decltype(test(last, last,  mon)), void>{}, "");
+    static_assert(is_same<decltype(test(last, last,  1_w)), void>{}, "");
+    static_assert(is_same<decltype(test(last, last,  1_y)), void>{}, "");
+    static_assert(is_same<decltype(test(last, last, last)), void>{}, "");
+
+}
diff --git a/third_party/date-3.0.1/test/iso_week/weekday.pass.cpp b/third_party/date-3.0.1/test/iso_week/weekday.pass.cpp
new file mode 100644
index 00000000..25b3545c
--- /dev/null
+++ b/third_party/date-3.0.1/test/iso_week/weekday.pass.cpp
@@ -0,0 +1,227 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// class weekday
+// {
+//     unsigned char wd_;
+// public:
+//     explicit constexpr weekday(unsigned wd) noexcept;
+//     constexpr weekday(date::weekday wd) noexcept;
+//     constexpr weekday(const sys_days& dp) noexcept;
+//
+//     weekday& operator++()    noexcept;
+//     weekday  operator++(int) noexcept;
+//     weekday& operator--()    noexcept;
+//     weekday  operator--(int) noexcept;
+//
+//     weekday& operator+=(const days& d) noexcept;
+//     weekday& operator-=(const days& d) noexcept;
+//
+//     constexpr explicit operator unsigned() const noexcept;
+//     constexpr operator date::weekday() const noexcept;
+//     constexpr bool ok() const noexcept;
+//
+//     // tested with weekday_indexed
+//     constexpr weekday_indexed operator[](unsigned index) const noexcept;
+//     // tested with weekday_last
+//     constexpr weekday_last    operator[](last_spec)      const noexcept;
+// };
+
+// constexpr bool operator==(const weekday& x, const weekday& y) noexcept;
+// constexpr bool operator!=(const weekday& x, const weekday& y) noexcept;
+
+// constexpr weekday operator+(const weekday& x, const days&    y) noexcept;
+// constexpr weekday operator+(const days&    x, const weekday& y) noexcept;
+// constexpr weekday operator-(const weekday& x, const days&    y) noexcept;
+// constexpr days    operator-(const weekday& x, const weekday& y) noexcept;
+
+// std::ostream& operator<<(std::ostream& os, const weekday& wd);
+
+// constexpr weekday sun{7};
+// constexpr weekday mon{1};
+// constexpr weekday tue{2};
+// constexpr weekday wed{3};
+// constexpr weekday thu{4};
+// constexpr weekday fri{5};
+// constexpr weekday sat{6};
+
+#include "iso_week.h"
+#include "date.h"
+
+#include <cassert>
+#include <sstream>
+#include <type_traits>
+
+#include <iostream>
+
+static_assert( std::is_trivially_destructible<iso_week::weekday>{}, "");
+static_assert(!std::is_default_constructible<iso_week::weekday>{}, "");
+static_assert( std::is_trivially_copy_constructible<iso_week::weekday>{}, "");
+static_assert( std::is_trivially_copy_assignable<iso_week::weekday>{}, "");
+static_assert( std::is_trivially_move_constructible<iso_week::weekday>{}, "");
+static_assert( std::is_trivially_move_assignable<iso_week::weekday>{}, "");
+
+static_assert(std::is_trivially_copyable<iso_week::weekday>{}, "");
+static_assert(std::is_standard_layout<iso_week::weekday>{}, "");
+static_assert(std::is_literal_type<iso_week::weekday>{}, "");
+
+static_assert( std::is_nothrow_constructible<iso_week::weekday, unsigned>{}, "");
+static_assert( std::is_nothrow_constructible<iso_week::weekday, iso_week::sys_days>{}, "");
+static_assert( std::is_nothrow_constructible<iso_week::weekday, date::weekday>{}, "");
+static_assert( std::is_nothrow_constructible<date::weekday, iso_week::weekday>{}, "");
+static_assert( std::is_nothrow_constructible<unsigned, iso_week::weekday>{}, "");
+static_assert(!std::is_convertible<unsigned, iso_week::weekday>{}, "");
+static_assert( std::is_convertible<iso_week::sys_days, iso_week::weekday>{}, "");
+static_assert( std::is_convertible<iso_week::weekday, date::weekday>{}, "");
+static_assert( std::is_convertible<date::weekday, iso_week::weekday>{}, "");
+static_assert(!std::is_convertible<iso_week::weekday, unsigned>{}, "");
+static_assert(static_cast<unsigned>(iso_week::weekday{1u}) == 1, "");
+
+static_assert(!iso_week::weekday{0u}.ok(), "");
+static_assert( iso_week::weekday{1u}.ok(), "");
+static_assert( iso_week::weekday{2u}.ok(), "");
+static_assert( iso_week::weekday{3u}.ok(), "");
+static_assert( iso_week::weekday{4u}.ok(), "");
+static_assert( iso_week::weekday{5u}.ok(), "");
+static_assert( iso_week::weekday{6u}.ok(), "");
+static_assert( iso_week::weekday{7u}.ok(), "");
+
+void
+test_weekday_arithmetic()
+{
+    using namespace iso_week;
+    constexpr unsigned a[7][7] =
+    {// -    Mon Tue Wed Thu Fri Sat Sun
+     /*Mon*/ {0,  6,  5,  4,  3,  2,  1},
+     /*Tue*/ {1,  0,  6,  5,  4,  3,  2},
+     /*Wed*/ {2,  1,  0,  6,  5,  4,  3},
+     /*Thu*/ {3,  2,  1,  0,  6,  5,  4},
+     /*Fri*/ {4,  3,  2,  1,  0,  6,  5},
+     /*Sat*/ {5,  4,  3,  2,  1,  0,  6},
+     /*Sun*/ {6,  5,  4,  3,  2,  1,  0}
+    };
+    for (unsigned x = 1; x <= 7; ++x)
+    {
+        for (unsigned y = 1; y <= 7; ++y)
+        {
+            assert(weekday{x} - weekday{y} == days{a[x-1][y-1]});
+            assert(weekday{x} - days{a[x-1][y-1]} == weekday{y});
+            assert(weekday{x} == weekday{y} + days{a[x-1][y-1]});
+            assert(weekday{x} == days{a[x-1][y-1]} + weekday{y});
+        }
+    }
+    for (unsigned x = 1; x <= 7; ++x)
+    {
+        for (int y = -21; y < 21; ++y)
+        {
+            weekday wx{x};
+            days dy{y};
+            wx += dy;
+            weekday wz = weekday{x} + days{y};
+            assert(wx.ok());
+            assert(wz.ok());
+            assert(wx == wz);
+            assert(wx - weekday{x} == days{y % 7 + (y % 7 < 0 ? 7 : 0)});
+        }
+    }
+    for (unsigned x = 1; x <= 7; ++x)
+    {
+        for (int y = -21; y < 21; ++y)
+        {
+            weekday wx{x};
+            days dy{y};
+            wx -= dy;
+            assert(wx == weekday{x} + days{-y});
+        }
+    }
+    for (unsigned x = 1; x <= 7; ++x)
+    {
+        weekday wx{x};
+        assert(++wx - weekday{x} == days{1});
+        assert(wx++ - weekday{x} == days{1});
+        assert(wx - weekday{x} == days{2});
+        assert(wx-- - weekday{x} == days{2});
+        assert(wx - weekday{x} == days{1});
+        assert(--wx - weekday{x} == days{0});
+    }
+}
+
+void
+test_with_date_weekday()
+{
+    auto constexpr d1 = iso_week::sun;
+    static_assert(unsigned{d1} == 7, "");
+    auto constexpr d2 = date::weekday{d1};
+    static_assert(d2 == date::Sunday, "");
+    auto constexpr d3 = iso_week::weekday{d2};
+    static_assert(unsigned{d3} == 7, "");
+}
+
+int
+main()
+{
+    using namespace iso_week;
+
+    static_assert(sun == weekday{7u}, "");
+    static_assert(mon == weekday{1u}, "");
+    static_assert(tue == weekday{2u}, "");
+    static_assert(wed == weekday{3u}, "");
+    static_assert(thu == weekday{4u}, "");
+    static_assert(fri == weekday{5u}, "");
+    static_assert(sat == weekday{6u}, "");
+
+    static_assert(!(sun != sun), "");
+    static_assert(  sun != mon, "");
+    static_assert(  mon != sun, "");
+
+    test_weekday_arithmetic();
+    test_with_date_weekday();
+
+    std::ostringstream os;
+
+    os << sun;
+    assert(os.str() == "Sun");
+    os.str("");
+
+    os << mon;
+    assert(os.str() == "Mon");
+    os.str("");
+
+    os << tue;
+    assert(os.str() == "Tue");
+    os.str("");
+
+    os << wed;
+    assert(os.str() == "Wed");
+    os.str("");
+
+    os << thu;
+    assert(os.str() == "Thu");
+    os.str("");
+
+    os << fri;
+    assert(os.str() == "Fri");
+    os.str("");
+
+    os << sat;
+    assert(os.str() == "Sat");
+}
diff --git a/third_party/date-3.0.1/test/iso_week/weekday_lessthan.fail.cpp b/third_party/date-3.0.1/test/iso_week/weekday_lessthan.fail.cpp
new file mode 100644
index 00000000..ff74e166
--- /dev/null
+++ b/third_party/date-3.0.1/test/iso_week/weekday_lessthan.fail.cpp
@@ -0,0 +1,32 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// weekday < weekday not allowed
+
+#include "iso_week.h"
+
+int
+main()
+{
+    using namespace iso_week;
+    auto b = sun < mon;
+}
diff --git a/third_party/date-3.0.1/test/iso_week/weekday_sum.fail.cpp b/third_party/date-3.0.1/test/iso_week/weekday_sum.fail.cpp
new file mode 100644
index 00000000..648af12b
--- /dev/null
+++ b/third_party/date-3.0.1/test/iso_week/weekday_sum.fail.cpp
@@ -0,0 +1,32 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// weekday + weekday not allowed
+
+#include "iso_week.h"
+
+int
+main()
+{
+    using namespace iso_week;
+    auto b = sun + mon;
+}
diff --git a/third_party/date-3.0.1/test/iso_week/weeknum.pass.cpp b/third_party/date-3.0.1/test/iso_week/weeknum.pass.cpp
new file mode 100644
index 00000000..5e60d77e
--- /dev/null
+++ b/third_party/date-3.0.1/test/iso_week/weeknum.pass.cpp
@@ -0,0 +1,121 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// class weeknum
+// {
+//     unsigned char wn_;
+//
+// public:
+//     explicit constexpr weeknum(unsigned wn) noexcept;
+//
+//     weeknum& operator++()    noexcept;
+//     weeknum  operator++(int) noexcept;
+//     weeknum& operator--()    noexcept;
+//     weeknum  operator--(int) noexcept;
+//
+//     weeknum& operator+=(const weeks& y) noexcept;
+//     weeknum& operator-=(const weeks& y) noexcept;
+//
+//     constexpr explicit operator unsigned() const noexcept;
+//     constexpr bool ok() const noexcept;
+// };
+//
+// constexpr bool operator==(const weeknum& x, const weeknum& y) noexcept;
+// constexpr bool operator!=(const weeknum& x, const weeknum& y) noexcept;
+// constexpr bool operator< (const weeknum& x, const weeknum& y) noexcept;
+// constexpr bool operator> (const weeknum& x, const weeknum& y) noexcept;
+// constexpr bool operator<=(const weeknum& x, const weeknum& y) noexcept;
+// constexpr bool operator>=(const weeknum& x, const weeknum& y) noexcept;
+//
+// constexpr weeknum  operator+(const weeknum& x, const weeks&   y) noexcept;
+// constexpr weeknum  operator+(const weeks&   x, const weeknum& y) noexcept;
+// constexpr weeknum  operator-(const weeknum& x, const weeks&   y) noexcept;
+// constexpr weeks    operator-(const weeknum& x, const weeknum& y) noexcept;
+//
+// std::ostream& operator<<(std::ostream& os, const weeknum& wn);
+//
+// constexpr weeknum operator "" _w(unsigned long long wn) noexcept;
+
+#include "iso_week.h"
+
+#include <cassert>
+#include <sstream>
+#include <type_traits>
+
+static_assert( std::is_trivially_destructible<iso_week::weeknum>{}, "");
+static_assert(!std::is_default_constructible<iso_week::weeknum>{}, "");
+static_assert( std::is_trivially_copy_constructible<iso_week::weeknum>{}, "");
+static_assert( std::is_trivially_copy_assignable<iso_week::weeknum>{}, "");
+static_assert( std::is_trivially_move_constructible<iso_week::weeknum>{}, "");
+static_assert( std::is_trivially_move_assignable<iso_week::weeknum>{}, "");
+
+static_assert(std::is_trivially_copyable<iso_week::weeknum>{}, "");
+static_assert(std::is_standard_layout<iso_week::weeknum>{}, "");
+static_assert(std::is_literal_type<iso_week::weeknum>{}, "");
+
+static_assert( std::is_nothrow_constructible<iso_week::weeknum, unsigned>{}, "");
+static_assert(!std::is_convertible<unsigned, iso_week::weeknum>{}, "");
+static_assert( std::is_nothrow_constructible<unsigned, iso_week::weeknum>{}, "");
+static_assert(!std::is_convertible<iso_week::weeknum, unsigned>{}, "");
+static_assert(static_cast<unsigned>(iso_week::weeknum{3}) == 3, "");
+
+int
+main()
+{
+    using namespace iso_week;
+    using namespace std::chrono;
+
+    static_assert(weeknum{2} == 2_w, "");
+    static_assert(unsigned{weeknum{2}} == 2, "");
+    static_assert(unsigned{weeknum{3}} == 3, "");
+    static_assert(weeknum{2} != 3_w, "");
+    static_assert(weeknum{2} < 3_w, "");
+    static_assert(weeknum{3} > 2_w, "");
+    static_assert(weeknum{2} <= 2_w, "");
+    static_assert(weeknum{3} >= 2_w, "");
+
+    auto wn = weeknum{4};
+    assert(++wn == weeknum{5});
+    assert(wn == weeknum{5});
+    assert(wn++ == weeknum{5});
+    assert(wn == weeknum{6});
+    assert(--wn == weeknum{5});
+    assert(wn == weeknum{5});
+    assert(wn-- == weeknum{5});
+    assert(wn == weeknum{4});
+
+    static_assert(!weeknum{0}.ok(), "");
+    static_assert( weeknum{1}.ok(), "");
+    static_assert( weeknum{53}.ok(), "");
+    static_assert(!weeknum{54}.ok(), "");
+
+    static_assert(15_w - 10_w == weeks{5}, "");
+    static_assert(15_w - weeks{5} == 10_w, "");
+    static_assert(15_w == weeks{5} + 10_w, "");
+    static_assert(15_w == 10_w + weeks{5}, "");
+    static_assert(10_w - 15_w == -weeks{5}, "");
+
+    auto w = 5_w;
+    std::ostringstream os;
+    os << w;
+    assert(os.str() == "W05");
+}
diff --git a/third_party/date-3.0.1/test/iso_week/weeknum_p_weeknum.fail.cpp b/third_party/date-3.0.1/test/iso_week/weeknum_p_weeknum.fail.cpp
new file mode 100644
index 00000000..2199aa33
--- /dev/null
+++ b/third_party/date-3.0.1/test/iso_week/weeknum_p_weeknum.fail.cpp
@@ -0,0 +1,32 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// weeknum + weeknum not allowed
+
+#include "iso_week.h"
+
+int
+main()
+{
+    using namespace iso_week;
+    auto x = 3_w + 4_w;
+}
diff --git a/third_party/date-3.0.1/test/iso_week/weeknum_weekday.pass.cpp b/third_party/date-3.0.1/test/iso_week/weeknum_weekday.pass.cpp
new file mode 100644
index 00000000..c02c093c
--- /dev/null
+++ b/third_party/date-3.0.1/test/iso_week/weeknum_weekday.pass.cpp
@@ -0,0 +1,86 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// class weeknum_weekday
+// {
+//     iso_week::weeknum wn_;  // exposition only
+//     iso_week::weekday wd_;  // exposition only
+//
+// public:
+//     constexpr weeknum_weekday(const iso_week::weeknum& wn,
+//                               const iso_week::weekday& wd) noexcept;
+//
+//     constexpr iso_week::weeknum weeknum() const noexcept;
+//     constexpr iso_week::weekday weekday() const noexcept;
+//
+//     constexpr bool ok() const noexcept;
+// };
+//
+// constexpr bool operator==(const weeknum_weekday& x, const weeknum_weekday& y) noexcept;
+// constexpr bool operator!=(const weeknum_weekday& x, const weeknum_weekday& y) noexcept;
+// constexpr bool operator< (const weeknum_weekday& x, const weeknum_weekday& y) noexcept;
+// constexpr bool operator> (const weeknum_weekday& x, const weeknum_weekday& y) noexcept;
+// constexpr bool operator<=(const weeknum_weekday& x, const weeknum_weekday& y) noexcept;
+// constexpr bool operator>=(const weeknum_weekday& x, const weeknum_weekday& y) noexcept;
+//
+// std::ostream& operator<<(std::ostream& os, const weeknum_weekday& md);
+
+#include "iso_week.h"
+
+#include <cassert>
+#include <sstream>
+#include <type_traits>
+
+static_assert( std::is_trivially_destructible<iso_week::weeknum_weekday>{}, "");
+static_assert(!std::is_default_constructible<iso_week::weeknum_weekday>{}, "");
+static_assert( std::is_trivially_copy_constructible<iso_week::weeknum_weekday>{}, "");
+static_assert( std::is_trivially_copy_assignable<iso_week::weeknum_weekday>{}, "");
+static_assert( std::is_trivially_move_constructible<iso_week::weeknum_weekday>{}, "");
+static_assert( std::is_trivially_move_assignable<iso_week::weeknum_weekday>{}, "");
+
+static_assert(std::is_trivially_copyable<iso_week::weeknum_weekday>{}, "");
+static_assert(std::is_standard_layout<iso_week::weeknum_weekday>{}, "");
+static_assert(std::is_literal_type<iso_week::weeknum_weekday>{}, "");
+
+static_assert( std::is_nothrow_constructible<iso_week::weeknum_weekday,
+                                                 iso_week::weeknum,
+                                                 iso_week::weekday>{}, "");
+
+int
+main()
+{
+    using namespace iso_week;
+
+    constexpr auto wn_wd = weeknum_weekday{52_w, tue};
+    static_assert(wn_wd.weeknum() == 52_w, "");
+    static_assert(wn_wd.weekday() == tue, "");
+
+    static_assert(wn_wd.ok(), "");
+
+    static_assert(wn_wd == weeknum_weekday{52_w, tue}, "");
+    static_assert(!(wn_wd != weeknum_weekday{52_w, tue}), "");
+    static_assert(wn_wd < weeknum_weekday{52_w, wed}, "");
+
+    std::ostringstream os;
+    os << wn_wd;
+    assert(os.str() == "W52-Tue");
+}
diff --git a/third_party/date-3.0.1/test/iso_week/year.pass.cpp b/third_party/date-3.0.1/test/iso_week/year.pass.cpp
new file mode 100644
index 00000000..1f1675ab
--- /dev/null
+++ b/third_party/date-3.0.1/test/iso_week/year.pass.cpp
@@ -0,0 +1,120 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// class year
+// {
+// public:
+//     explicit constexpr year(int y) noexcept;
+//
+//     year& operator++()    noexcept;
+//     year  operator++(int) noexcept;
+//     year& operator--()    noexcept;
+//     year  operator--(int) noexcept;
+//
+//     year& operator+=(const years& y) noexcept;
+//     year& operator-=(const years& y) noexcept;
+//
+//     constexpr explicit operator int() const noexcept;
+//     constexpr bool ok() const noexcept;
+//
+//     static constexpr year min() noexcept;
+//     static constexpr year max() noexcept;
+// };
+
+// constexpr bool operator==(const year& x, const year& y) noexcept;
+// constexpr bool operator!=(const year& x, const year& y) noexcept;
+// constexpr bool operator< (const year& x, const year& y) noexcept;
+// constexpr bool operator> (const year& x, const year& y) noexcept;
+// constexpr bool operator<=(const year& x, const year& y) noexcept;
+// constexpr bool operator>=(const year& x, const year& y) noexcept;
+
+// constexpr year  operator+(const year&  x, const years& y) noexcept;
+// constexpr year  operator+(const years& x, const year&  y) noexcept;
+// constexpr year  operator-(const year&  x, const years& y) noexcept;
+// constexpr years operator-(const year&  x, const year&  y) noexcept;
+
+// std::ostream& operator<<(std::ostream& os, const year& y);
+// inline namespace literals {
+// constexpr year operator "" _y(unsigned long long y) noexcept;
+// }
+
+#include "iso_week.h"
+
+#include <cassert>
+#include <sstream>
+#include <type_traits>
+
+static_assert( std::is_trivially_destructible<iso_week::year>{}, "");
+static_assert(!std::is_default_constructible<iso_week::year>{}, "");
+static_assert( std::is_trivially_copy_constructible<iso_week::year>{}, "");
+static_assert( std::is_trivially_copy_assignable<iso_week::year>{}, "");
+static_assert( std::is_trivially_move_constructible<iso_week::year>{}, "");
+static_assert( std::is_trivially_move_assignable<iso_week::year>{}, "");
+
+static_assert(std::is_trivially_copyable<iso_week::year>{}, "");
+static_assert(std::is_standard_layout<iso_week::year>{}, "");
+static_assert(std::is_literal_type<iso_week::year>{}, "");
+
+static_assert( std::is_nothrow_constructible<iso_week::year, int>{}, "");
+static_assert(!std::is_convertible<int, iso_week::year>{}, "");
+static_assert( std::is_nothrow_constructible<int, iso_week::year>{}, "");
+static_assert(!std::is_convertible<iso_week::year, int>{}, "");
+static_assert(static_cast<int>(iso_week::year{-1}) == -1, "");
+
+int
+main()
+{
+    using namespace iso_week;
+
+    static_assert(year{2015} == 2015_y, "");
+    static_assert(int{year{2015}} == 2015, "");
+    static_assert(year{2015} != 2016_y, "");
+    static_assert(year{2015} < 2016_y, "");
+    static_assert(year{2016} > 2015_y, "");
+    static_assert(year{2015} <= 2015_y, "");
+    static_assert(year{2016} >= 2015_y, "");
+
+    auto y = year{2014};
+    assert(++y == year{2015});
+    assert(y == year{2015});
+    assert(y++ == year{2015});
+    assert(y == year{2016});
+    assert(--y == year{2015});
+    assert(y == year{2015});
+    assert(y-- == year{2015});
+    assert(y == year{2014});
+
+    static_assert(year::min().ok(), "");
+    static_assert(year{2015}.ok(), "");
+    static_assert(year{2016}.ok(), "");
+    static_assert(year::max().ok(), "");
+
+    static_assert(2015_y - 2010_y == years{5}, "");
+    static_assert(2015_y - years{5} == 2010_y, "");
+    static_assert(2015_y == years{5} + 2010_y, "");
+    static_assert(2015_y == 2010_y + years{5}, "");
+
+    y = 2015_y;
+    std::ostringstream os;
+    os << y;
+    assert(os.str() == "2015");
+}
diff --git a/third_party/date-3.0.1/test/iso_week/year_lastweek.pass.cpp b/third_party/date-3.0.1/test/iso_week/year_lastweek.pass.cpp
new file mode 100644
index 00000000..88744720
--- /dev/null
+++ b/third_party/date-3.0.1/test/iso_week/year_lastweek.pass.cpp
@@ -0,0 +1,97 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// class year_lastweek
+// {
+//     iso_week::year y_;
+//
+// public:
+//     explicit constexpr year_lastweek(const iso_week::year& y) noexcept;
+//
+//     constexpr iso_week::year    year()    const noexcept;
+//     constexpr iso_week::weeknum weeknum() const noexcept;
+//
+//     year_lastweek& operator+=(const years& dy) noexcept;
+//     year_lastweek& operator-=(const years& dy) noexcept;
+//
+//     constexpr bool ok() const noexcept;
+// };
+//
+// constexpr bool operator==(const year_lastweek& x, const year_lastweek& y) noexcept;
+// constexpr bool operator!=(const year_lastweek& x, const year_lastweek& y) noexcept;
+// constexpr bool operator< (const year_lastweek& x, const year_lastweek& y) noexcept;
+// constexpr bool operator> (const year_lastweek& x, const year_lastweek& y) noexcept;
+// constexpr bool operator<=(const year_lastweek& x, const year_lastweek& y) noexcept;
+// constexpr bool operator>=(const year_lastweek& x, const year_lastweek& y) noexcept;
+//
+// constexpr year_lastweek operator+(const year_lastweek& ym, const years& dy) noexcept;
+// constexpr year_lastweek operator+(const years& dy, const year_lastweek& ym) noexcept;
+// constexpr year_lastweek operator-(const year_lastweek& ym, const years& dy) noexcept;
+//
+// std::ostream& operator<<(std::ostream& os, const year_lastweek& ym);
+
+#include "iso_week.h"
+
+#include <cassert>
+#include <sstream>
+#include <type_traits>
+
+static_assert( std::is_trivially_destructible<iso_week::year_lastweek>{}, "");
+static_assert(!std::is_default_constructible<iso_week::year_lastweek>{}, "");
+static_assert( std::is_trivially_copy_constructible<iso_week::year_lastweek>{}, "");
+static_assert( std::is_trivially_copy_assignable<iso_week::year_lastweek>{}, "");
+static_assert( std::is_trivially_move_constructible<iso_week::year_lastweek>{}, "");
+static_assert( std::is_trivially_move_assignable<iso_week::year_lastweek>{}, "");
+
+static_assert(std::is_trivially_copyable<iso_week::year_lastweek>{}, "");
+static_assert(std::is_standard_layout<iso_week::year_lastweek>{}, "");
+static_assert(std::is_literal_type<iso_week::year_lastweek>{}, "");
+
+static_assert(std::is_nothrow_constructible<iso_week::year_lastweek,
+                                                iso_week::year>{}, "");
+static_assert(!std::is_convertible<iso_week::year, iso_week::year_lastweek>{}, "");
+
+int
+main()
+{
+    using namespace iso_week;
+
+    constexpr auto y_wn = year_lastweek{2015_y};
+    static_assert(y_wn.year() == 2015_y, "");
+    static_assert(y_wn.weeknum() == 53_w, "");
+    static_assert(year_lastweek{2016_y}.weeknum() == 52_w, "");
+
+    static_assert(y_wn.ok(), "");
+
+    static_assert(y_wn == year_lastweek{2015_y}, "");
+    static_assert(!(y_wn != year_lastweek{2015_y}), "");
+    static_assert(y_wn < year_lastweek{2016_y}, "");
+
+    auto y_wn2 = y_wn + years{2};
+    assert(y_wn2 == year_lastweek{2017_y});
+    y_wn2 -= years{1};
+    assert(y_wn2 == year_lastweek{2016_y});
+
+    std::ostringstream os;
+    os << y_wn;
+    assert(os.str() == "2015-W last");
+}
diff --git a/third_party/date-3.0.1/test/iso_week/year_lastweek_weekday.pass.cpp b/third_party/date-3.0.1/test/iso_week/year_lastweek_weekday.pass.cpp
new file mode 100644
index 00000000..5f65f6fd
--- /dev/null
+++ b/third_party/date-3.0.1/test/iso_week/year_lastweek_weekday.pass.cpp
@@ -0,0 +1,129 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// class year_lastweek_weekday
+// {
+// public:
+//     constexpr year_lastweek_weekday(const iso_week::year& y,
+//                                     const iso_week::weekday& wd) noexcept;
+//
+//     year_lastweek_weekday& operator+=(const years& y) noexcept;
+//     year_lastweek_weekday& operator-=(const years& y) noexcept;
+//
+//     constexpr iso_week::year    year()    const noexcept;
+//     constexpr iso_week::weeknum weeknum() const noexcept;
+//     constexpr iso_week::weekday weekday() const noexcept;
+//
+//     constexpr operator sys_days() const noexcept;
+//     constexpr bool ok() const noexcept;
+// };
+//
+// constexpr bool operator==(const year_lastweek_weekday& x, const year_lastweek_weekday& y) noexcept;
+// constexpr bool operator!=(const year_lastweek_weekday& x, const year_lastweek_weekday& y) noexcept;
+// constexpr bool operator< (const year_lastweek_weekday& x, const year_lastweek_weekday& y) noexcept;
+// constexpr bool operator> (const year_lastweek_weekday& x, const year_lastweek_weekday& y) noexcept;
+// constexpr bool operator<=(const year_lastweek_weekday& x, const year_lastweek_weekday& y) noexcept;
+// constexpr bool operator>=(const year_lastweek_weekday& x, const year_lastweek_weekday& y) noexcept;
+//
+// constexpr year_lastweek_weekday operator+(const year_lastweek_weekday& x, const years& y) noexcept;
+// constexpr year_lastweek_weekday operator+(const years& y, const year_lastweek_weekday& x) noexcept;
+// constexpr year_lastweek_weekday operator-(const year_lastweek_weekday& x, const years& y) noexcept;
+//
+// std::ostream& operator<<(std::ostream& os, const year_lastweek_weekday& x);
+
+#include "iso_week.h"
+
+#include <cassert>
+#include <sstream>
+#include <type_traits>
+
+static_assert( std::is_trivially_destructible<iso_week::year_lastweek_weekday>{}, "");
+static_assert(!std::is_default_constructible<iso_week::year_lastweek_weekday>{}, "");
+static_assert( std::is_trivially_copy_constructible<iso_week::year_lastweek_weekday>{}, "");
+static_assert( std::is_trivially_copy_assignable<iso_week::year_lastweek_weekday>{}, "");
+static_assert( std::is_trivially_move_constructible<iso_week::year_lastweek_weekday>{}, "");
+static_assert( std::is_trivially_move_assignable<iso_week::year_lastweek_weekday>{}, "");
+
+static_assert(std::is_trivially_copyable<iso_week::year_lastweek_weekday>{}, "");
+static_assert(std::is_standard_layout<iso_week::year_lastweek_weekday>{}, "");
+static_assert(std::is_literal_type<iso_week::year_lastweek_weekday>{}, "");
+
+static_assert( std::is_nothrow_constructible<iso_week::year_lastweek_weekday,
+                                                 iso_week::year, iso_week::weekday>{}, "");
+static_assert( std::is_nothrow_constructible<iso_week::sys_days,
+                                                 iso_week::year_lastweek_weekday>{}, "");
+static_assert( std::is_convertible<iso_week::year_lastweek_weekday,
+                                       iso_week::sys_days>{}, "");
+
+int
+main()
+{
+    using namespace iso_week;
+
+    constexpr auto x0 = year_lastweek_weekday{2015_y, tue};
+    static_assert(x0.year() == 2015_y, "");
+    static_assert(x0.weeknum() == 53_w, "");
+    static_assert(x0.weekday() == tue, "");
+
+    auto x3 = x0;
+    x3 += years{2};
+    assert(x3.year() == 2017_y);
+    assert(x3.weeknum() == 52_w);
+    assert(x3.weekday() == tue);
+
+    x3 -= years{1};
+    assert(x3.year() == 2016_y);
+    assert(x3.weeknum() == 52_w);
+    assert(x3.weekday() == tue);
+
+    x3 -= years{1};
+    assert(x3.year() == 2015_y);
+    assert(x3.weeknum() == 53_w);
+    assert(x3.weekday() == tue);
+
+    constexpr sys_days dp = 2015_y/last/wed;
+    static_assert(dp == sys_days{days{16799}}, "");
+
+    static_assert(x0.ok(), "");
+    assert(x3.ok());
+
+    static_assert(2015_y/last/mon < 2015_y/last/sun, "");
+
+    static_assert(x0 + years{3} == 2018_y/last/tue, "");
+    static_assert(years{3} + x0 == 2018_y/last/tue, "");
+    static_assert(x0 - years{3} == 2012_y/last/tue, "");
+
+    std::ostringstream os;
+    os << x0;
+    assert(os.str() == "2015-W last-Tue");
+
+    for (auto y = 1950_y; y <= 2050_y; ++y)
+    {
+        auto wd = mon;
+        do
+        {
+            auto x = y/last/wd;
+            assert(date::year_month_day{x} == date::year_month_day{year_weeknum_weekday{x}});
+            ++wd;
+        } while (wd != mon);
+    }
+}
diff --git a/third_party/date-3.0.1/test/iso_week/year_p_year.fail.cpp b/third_party/date-3.0.1/test/iso_week/year_p_year.fail.cpp
new file mode 100644
index 00000000..c0eba47b
--- /dev/null
+++ b/third_party/date-3.0.1/test/iso_week/year_p_year.fail.cpp
@@ -0,0 +1,32 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// year + year not allowed
+
+#include "iso_week.h"
+
+int
+main()
+{
+    using namespace iso_week;
+    auto x = 2015_y + 2015_y;
+}
diff --git a/third_party/date-3.0.1/test/iso_week/year_weeknum.pass.cpp b/third_party/date-3.0.1/test/iso_week/year_weeknum.pass.cpp
new file mode 100644
index 00000000..6e9d4b66
--- /dev/null
+++ b/third_party/date-3.0.1/test/iso_week/year_weeknum.pass.cpp
@@ -0,0 +1,97 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// class year_weeknum
+// {
+//     iso_week::year    y_;
+//     iso_week::weeknum wn_;
+//
+// public:
+//     constexpr year_weeknum(const iso_week::year& y, const iso_week::weeknum& wn) noexcept;
+//
+//     constexpr iso_week::year    year()    const noexcept;
+//     constexpr iso_week::weeknum weeknum() const noexcept;
+//
+//     year_weeknum& operator+=(const years& dy) noexcept;
+//     year_weeknum& operator-=(const years& dy) noexcept;
+//
+//     constexpr bool ok() const noexcept;
+// };
+//
+// constexpr bool operator==(const year_weeknum& x, const year_weeknum& y) noexcept;
+// constexpr bool operator!=(const year_weeknum& x, const year_weeknum& y) noexcept;
+// constexpr bool operator< (const year_weeknum& x, const year_weeknum& y) noexcept;
+// constexpr bool operator> (const year_weeknum& x, const year_weeknum& y) noexcept;
+// constexpr bool operator<=(const year_weeknum& x, const year_weeknum& y) noexcept;
+// constexpr bool operator>=(const year_weeknum& x, const year_weeknum& y) noexcept;
+//
+// constexpr year_weeknum operator+(const year_weeknum& ym, const years& dy) noexcept;
+// constexpr year_weeknum operator+(const years& dy, const year_weeknum& ym) noexcept;
+// constexpr year_weeknum operator-(const year_weeknum& ym, const years& dy) noexcept;
+//
+// std::ostream& operator<<(std::ostream& os, const year_weeknum& ym);
+
+#include "iso_week.h"
+
+#include <cassert>
+#include <sstream>
+#include <type_traits>
+
+static_assert( std::is_trivially_destructible<iso_week::year_weeknum>{}, "");
+static_assert(!std::is_default_constructible<iso_week::year_weeknum>{}, "");
+static_assert( std::is_trivially_copy_constructible<iso_week::year_weeknum>{}, "");
+static_assert( std::is_trivially_copy_assignable<iso_week::year_weeknum>{}, "");
+static_assert( std::is_trivially_move_constructible<iso_week::year_weeknum>{}, "");
+static_assert( std::is_trivially_move_assignable<iso_week::year_weeknum>{}, "");
+
+static_assert(std::is_trivially_copyable<iso_week::year_weeknum>{}, "");
+static_assert(std::is_standard_layout<iso_week::year_weeknum>{}, "");
+static_assert(std::is_literal_type<iso_week::year_weeknum>{}, "");
+
+static_assert( std::is_nothrow_constructible<iso_week::year_weeknum,
+                                                 iso_week::year,
+                                                 iso_week::weeknum>{}, "");
+
+int
+main()
+{
+    using namespace iso_week;
+
+    constexpr auto y_wn = year_weeknum{2015_y, 52_w};
+    static_assert(y_wn.year() == 2015_y, "");
+    static_assert(y_wn.weeknum() == 52_w, "");
+
+    static_assert(y_wn.ok(), "");
+
+    static_assert(y_wn == year_weeknum{2015_y, 52_w}, "");
+    static_assert(!(y_wn != year_weeknum{2015_y, 52_w}), "");
+    static_assert(y_wn < year_weeknum{2015_y, 53_w}, "");
+
+    auto y_wn2 = y_wn + years{2};
+    assert((y_wn2 == year_weeknum{2017_y, 52_w}));
+    y_wn2 -= years{1};
+    assert((y_wn2 == year_weeknum{2016_y, 52_w}));
+
+    std::ostringstream os;
+    os << y_wn;
+    assert(os.str() == "2015-W52");
+}
diff --git a/third_party/date-3.0.1/test/iso_week/year_weeknum_weekday.pass.cpp b/third_party/date-3.0.1/test/iso_week/year_weeknum_weekday.pass.cpp
new file mode 100644
index 00000000..0540f976
--- /dev/null
+++ b/third_party/date-3.0.1/test/iso_week/year_weeknum_weekday.pass.cpp
@@ -0,0 +1,139 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// class year_weeknum_weekday
+
+// class year_weeknum_weekday
+// {
+// public:
+//     constexpr year_weeknum_weekday(const iso_week::year& y, const iso_week::weeknum& wn,
+//                                    const iso_week::weekday& wd) noexcept;
+//     constexpr year_weeknum_weekday(const year_lastweek_weekday& ylwwd) noexcept;
+//     constexpr year_weeknum_weekday(const sys_days& dp) noexcept;
+//
+//     year_weeknum_weekday& operator+=(const years& y) noexcept;
+//     year_weeknum_weekday& operator-=(const years& y) noexcept;
+//
+//     constexpr iso_week::year    year()    const noexcept;
+//     constexpr iso_week::weeknum weeknum() const noexcept;
+//     constexpr iso_week::weekday weekday() const noexcept;
+//
+//     constexpr operator sys_days() const noexcept;
+//     constexpr bool ok() const noexcept;
+// };
+//
+// constexpr bool operator==(const year_weeknum_weekday& x, const year_weeknum_weekday& y) noexcept;
+// constexpr bool operator!=(const year_weeknum_weekday& x, const year_weeknum_weekday& y) noexcept;
+// constexpr bool operator< (const year_weeknum_weekday& x, const year_weeknum_weekday& y) noexcept;
+// constexpr bool operator> (const year_weeknum_weekday& x, const year_weeknum_weekday& y) noexcept;
+// constexpr bool operator<=(const year_weeknum_weekday& x, const year_weeknum_weekday& y) noexcept;
+// constexpr bool operator>=(const year_weeknum_weekday& x, const year_weeknum_weekday& y) noexcept;
+//
+// constexpr year_weeknum_weekday operator+(const year_weeknum_weekday& ywnwd, const years& y) noexcept;
+// constexpr year_weeknum_weekday operator+(const years& y, const year_weeknum_weekday& ywnwd) noexcept;
+// constexpr year_weeknum_weekday operator-(const year_weeknum_weekday& ywnwd, const years& y) noexcept;
+//
+// std::ostream& operator<<(std::ostream& os, const year_weeknum_weekday& ywnwd);
+
+#include "iso_week.h"
+
+#include <cassert>
+#include <sstream>
+#include <type_traits>
+
+static_assert( std::is_trivially_destructible<iso_week::year_weeknum_weekday>{}, "");
+static_assert(!std::is_default_constructible<iso_week::year_weeknum_weekday>{}, "");
+static_assert( std::is_trivially_copy_constructible<iso_week::year_weeknum_weekday>{}, "");
+static_assert( std::is_trivially_copy_assignable<iso_week::year_weeknum_weekday>{}, "");
+static_assert( std::is_trivially_move_constructible<iso_week::year_weeknum_weekday>{}, "");
+static_assert( std::is_trivially_move_assignable<iso_week::year_weeknum_weekday>{}, "");
+
+static_assert(std::is_trivially_copyable<iso_week::year_weeknum_weekday>{}, "");
+static_assert(std::is_standard_layout<iso_week::year_weeknum_weekday>{}, "");
+static_assert(std::is_literal_type<iso_week::year_weeknum_weekday>{}, "");
+
+static_assert( std::is_nothrow_constructible<iso_week::year_weeknum_weekday,
+                                                 iso_week::year, iso_week::weeknum,
+                                                 iso_week::weekday>{}, "");
+static_assert( std::is_nothrow_constructible<iso_week::year_weeknum_weekday,
+                                                 iso_week::year_lastweek_weekday>{}, "");
+static_assert( std::is_convertible<iso_week::year_lastweek_weekday,
+                                       iso_week::year_weeknum_weekday>{}, "");
+static_assert( std::is_nothrow_constructible<iso_week::year_weeknum_weekday,
+                                                 iso_week::sys_days>{}, "");
+static_assert( std::is_convertible<iso_week::sys_days,
+                                       iso_week::year_weeknum_weekday>{}, "");
+static_assert( std::is_nothrow_constructible<iso_week::sys_days,
+                                                 iso_week::year_weeknum_weekday>{}, "");
+static_assert( std::is_convertible<iso_week::year_weeknum_weekday,
+                                       iso_week::sys_days>{}, "");
+
+int
+main()
+{
+    using namespace iso_week;
+
+    constexpr auto x0 = year_weeknum_weekday{2015_y, 52_w, tue};
+    static_assert(x0.year() == 2015_y, "");
+    static_assert(x0.weeknum() == 52_w, "");
+    static_assert(x0.weekday() == tue, "");
+
+    constexpr auto x1 = year_weeknum_weekday{2015_y/last/tue};
+    static_assert(x1.year() == 2015_y, "");
+    static_assert(x1.weeknum() == 53_w, "");
+    static_assert(x1.weekday() == tue, "");
+
+    constexpr year_weeknum_weekday x2 = sys_days{days{16792}};
+    static_assert(x2.year() == 2015_y, "");
+    static_assert(x2.weeknum() == 52_w, "");
+    static_assert(x2.weekday() == wed, "");
+
+    auto x3 = x2;
+    x3 += years{2};
+    assert(x3.year() == 2017_y);
+    assert(x3.weeknum() == 52_w);
+    assert(x3.weekday() == wed);
+
+    x3 -= years{1};
+    assert(x3.year() == 2016_y);
+    assert(x3.weeknum() == 52_w);
+    assert(x3.weekday() == wed);
+
+    constexpr sys_days dp = 2015_y/52_w/wed;
+    static_assert(dp == sys_days{days{16792}}, "");
+
+    static_assert(x0.ok(), "");
+    static_assert(x1.ok(), "");
+    static_assert(x2.ok(), "");
+    assert(x3.ok());
+    static_assert(!(2016_y/53_w/sun).ok(), "");
+
+    static_assert(2015_y/52_w/mon < 2015_y/52_w/sun, "");
+
+    static_assert(x0 + years{3} == 2018_y/52_w/tue, "");
+    static_assert(years{3} + x0 == 2018_y/52_w/tue, "");
+    static_assert(x0 - years{3} == 2012_y/52_w/tue, "");
+
+    std::ostringstream os;
+    os << x0;
+    assert(os.str() == "2015-W52-Tue");
+}
diff --git a/third_party/date-3.0.1/test/iso_week/years_m_year.fail.cpp b/third_party/date-3.0.1/test/iso_week/years_m_year.fail.cpp
new file mode 100644
index 00000000..8eb43074
--- /dev/null
+++ b/third_party/date-3.0.1/test/iso_week/years_m_year.fail.cpp
@@ -0,0 +1,32 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// years - year not allowed
+
+#include "iso_week.h"
+
+int
+main()
+{
+    using namespace iso_week;
+    auto x = years{3} - 2015_y;
+}
diff --git a/third_party/date-3.0.1/test/just.pass.cpp b/third_party/date-3.0.1/test/just.pass.cpp
new file mode 100644
index 00000000..f31a8e96
--- /dev/null
+++ b/third_party/date-3.0.1/test/just.pass.cpp
@@ -0,0 +1,26 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+int
+main()
+{
+}
diff --git a/third_party/date-3.0.1/test/posix/ptz.pass.cpp b/third_party/date-3.0.1/test/posix/ptz.pass.cpp
new file mode 100644
index 00000000..5601c21d
--- /dev/null
+++ b/third_party/date-3.0.1/test/posix/ptz.pass.cpp
@@ -0,0 +1,108 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2021 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// Test Posix::time_zone
+
+#include "tz.h"
+#include "ptz.h"
+#include <cassert>
+
+bool
+is_equal(date::sys_info const& x, date::sys_info const& y)
+{
+    return x.begin == y.begin &&
+           x.end == y.end &&
+           x.offset == y.offset &&
+           x.save == y.save &&
+           x.abbrev == y.abbrev;
+}
+
+bool
+is_equal(date::local_info const& x, date::local_info const& y)
+{
+    return x.result == y.result && is_equal(x.first, y.first)
+                                && is_equal(x.second, y.second);
+}
+
+int
+main()
+{
+    using namespace date;
+    using namespace std;
+    using namespace std::chrono;
+
+    auto tzi = locate_zone("Australia/Sydney");
+    Posix::time_zone tzp{"AEST-10AEDT,M10.1.0,M4.1.0/3"};
+    auto tp = local_days{2021_y/1/1} + 0s;
+    assert(tzp.get_info(tp).result == local_info::unique);
+    assert(is_equal(tzi->get_info(tp), tzp.get_info(tp)));
+    
+    tp = local_days{2021_y/10/Sunday[1]} + 2h + 30min;
+    assert(tzp.get_info(tp).result == local_info::nonexistent);
+    assert(is_equal(tzi->get_info(tp), tzp.get_info(tp)));
+
+    tp = local_days{2021_y/4/Sunday[1]} + 2h + 30min;
+    assert(tzp.get_info(tp).result == local_info::ambiguous);
+    assert(is_equal(tzi->get_info(tp), tzp.get_info(tp)));
+
+    tp = local_days{2021_y/7/1};
+    assert(tzp.get_info(tp).result == local_info::unique);
+    assert(is_equal(tzi->get_info(tp), tzp.get_info(tp)));
+
+
+    tzi = locate_zone("America/New_York");
+    tzp = Posix::time_zone{"EST5EDT,M3.2.0,M11.1.0"};
+    tp = local_days{2021_y/1/1};
+    assert(tzp.get_info(tp).result == local_info::unique);
+    assert(is_equal(tzi->get_info(tp), tzp.get_info(tp)));
+
+    tp = local_days{2021_y/3/Sunday[2]} + 2h + 30min;
+    assert(tzp.get_info(tp).result == local_info::nonexistent);
+    assert(is_equal(tzi->get_info(tp), tzp.get_info(tp)));
+
+    tp = local_days{2021_y/11/Sunday[1]} + 1h + 30min;
+    assert(tzp.get_info(tp).result == local_info::ambiguous);
+    assert(is_equal(tzi->get_info(tp), tzp.get_info(tp)));
+
+    tp = local_days{2021_y/7/1};
+    assert(tzp.get_info(tp).result == local_info::unique);
+    assert(is_equal(tzi->get_info(tp), tzp.get_info(tp)));
+
+
+    tzi = locate_zone("Europe/Dublin");
+    tzp = Posix::time_zone{"IST-1GMT0,M10.5.0,M3.5.0/1"};
+    tp = local_days{2021_y/1/1};
+    assert(tzp.get_info(tp).result == local_info::unique);
+    assert(is_equal(tzi->get_info(tp), tzp.get_info(tp)));
+
+    tp = local_days{2021_y/3/Sunday[last]} + 1h + 30min;
+    assert(tzp.get_info(tp).result == local_info::nonexistent);
+    assert(is_equal(tzi->get_info(tp), tzp.get_info(tp)));
+
+    tp = local_days{2021_y/10/Sunday[last]} + 1h + 30min;
+    assert(tzp.get_info(tp).result == local_info::ambiguous);
+    assert(is_equal(tzi->get_info(tp), tzp.get_info(tp)));
+
+    tp = local_days{2021_y/7/1};
+    assert(tzp.get_info(tp).result == local_info::unique);
+    assert(is_equal(tzi->get_info(tp), tzp.get_info(tp)));
+}
diff --git a/third_party/date-3.0.1/test/solar_hijri_test/parse.pass.cpp b/third_party/date-3.0.1/test/solar_hijri_test/parse.pass.cpp
new file mode 100644
index 00000000..9a98209e
--- /dev/null
+++ b/third_party/date-3.0.1/test/solar_hijri_test/parse.pass.cpp
@@ -0,0 +1,237 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2020 Asad. Gharighi
+// Copyright (c) 2020 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+#include "date.h"
+#include "solar_hijri.h"
+#include "islamic.h"
+#include "tz.h"
+#include <cassert>
+#include <iostream>
+#include <chrono>
+#include <math.h>
+
+void
+test_a() {
+  constexpr auto civil = date::year{2020}/date::January/27;
+  using namespace solar_hijri;
+  static_assert(year_month_day{civil} == 1398_y/11/07, "");
+}
+
+void
+test_b() {
+  using namespace solar_hijri::literals;
+  static_assert(date::year_month_day{475_y/far/1} == date::year{1096}/03/21, "");
+  static_assert(date::year_month_weekday{475_y/far/1} ==
+                date::year{1096}/03/date::Saturday[3], "");
+}
+
+void
+test_c() {
+  using namespace solar_hijri;
+  auto date = solar_hijri::year_month_day{1398_y/bah/6};
+  for (auto i = 0; i < 24; i++) {
+    auto weekday = solar_hijri::weekday{date};
+    assert(date == 1398_y/11/06 + months{i});
+    assert(date.month() == month{(i+10u)%12 + 1});
+    assert(weekday == (weekday[1]/date.month()/date.year()).weekday());
+    auto k = weekday;
+    for (auto j = 0; j < 14; j++, k++) {
+      assert(weekday + days{j} == k);
+    }
+    date+=solar_hijri::months(1);
+  }
+}
+
+void
+test_d() {
+  auto zt = date::make_zoned(date::current_zone(), std::chrono::system_clock::now());
+  auto ld = date::floor<date::days>(zt.get_local_time());
+  solar_hijri::year_month_day ymd{ld};
+  auto time = date::make_time(zt.get_local_time() - ld);
+  (void)time;
+}
+
+void
+test_e() {
+  auto sd = date::floor<solar_hijri::days>(std::chrono::system_clock::now());
+  auto today = solar_hijri::year_month_day{sd};
+  assert(solar_hijri::year_month_weekday{today}.weekday() == solar_hijri::weekday{sd});
+}
+
+void
+test_f() {
+  constexpr auto isl = islamic::year{1441}/6/1;
+  using namespace solar_hijri;
+  static_assert(year_month_day{isl} == 1398_y/11/07, "");
+}
+
+void
+test_g() {
+  date::year_month_day ymdd[] = {
+    date::year{1583}/date::November/21,
+    date::year{1583}/date::November/22,
+    date::year{1583}/date::December/6,
+    date::year{1591}/date::December/26,
+    date::year{1616}/date::October/20,
+    date::year{1619}/date::October/13,
+    date::year{1627}/date::August/9,
+    date::year{1649}/date::October/15,
+    date::year{1657}/date::August/9,
+    date::year{1682}/date::June/23,
+    date::year{1691}/date::October/12,
+    date::year{1712}/date::September/13,
+    date::year{1718}/date::July/17,
+    date::year{1747}/date::January/4,
+    date::year{1756}/date::January/1,
+    date::year{1770}/date::January/15,
+    date::year{1798}/date::October/24,
+    date::year{1809}/date::July/11,
+    date::year{1834}/date::July/17,
+    date::year{1850}/date::September/9,
+    date::year{1865}/date::November/4,
+    date::year{1902}/date::December/21,
+    date::year{1926}/date::March/21,
+    date::year{1926}/date::March/22,
+    date::year{1957}/date::June/1,
+    date::year{1977}/date::March/7,
+    date::year{1982}/date::May/30,
+    date::year{1992}/date::December/8
+  };
+
+  solar_hijri::year_month_day ymdh[] = {
+    solar_hijri::year{962}/solar_hijri::Aban/30,
+    solar_hijri::year{962}/solar_hijri::Azar/1,
+    solar_hijri::year{962}/solar_hijri::Azar/15,
+    solar_hijri::year{970}/solar_hijri::Dey/5,
+    solar_hijri::year{995}/solar_hijri::Mehr/29,
+    solar_hijri::year{998}/solar_hijri::Mehr/21,
+    solar_hijri::year{1006}/solar_hijri::Mordad/18,
+    solar_hijri::year{1028}/solar_hijri::Mehr/24,
+    solar_hijri::year{1036}/solar_hijri::Mordad/19,
+    solar_hijri::year{1061}/solar_hijri::Tir/3,
+    solar_hijri::year{1070}/solar_hijri::Mehr/20,
+    solar_hijri::year{1091}/solar_hijri::Shahrivar/22,
+    solar_hijri::year{1097}/solar_hijri::Tir/26,
+    solar_hijri::year{1125}/solar_hijri::Dey/14,
+    solar_hijri::year{1134}/solar_hijri::Dey/11,
+    solar_hijri::year{1148}/solar_hijri::Dey/26,
+    solar_hijri::year{1177}/solar_hijri::Aban/2,
+    solar_hijri::year{1188}/solar_hijri::Tir/20,
+    solar_hijri::year{1213}/solar_hijri::Tir/26,
+    solar_hijri::year{1229}/solar_hijri::Shahrivar/18,
+    solar_hijri::year{1244}/solar_hijri::Aban/13,
+    solar_hijri::year{1281}/solar_hijri::Azar/29,
+    solar_hijri::year{1304}/solar_hijri::Esfand/30,
+    solar_hijri::year{1305}/solar_hijri::Farvardin/1,
+    solar_hijri::year{1336}/solar_hijri::Khordad/11,
+    solar_hijri::year{1355}/solar_hijri::Esfand/16,
+    solar_hijri::year{1361}/solar_hijri::Khordad/9,
+    solar_hijri::year{1371}/solar_hijri::Azar/17
+  };
+
+  solar_hijri::year_month_weekday ymdwd[] = {
+    solar_hijri::year{962}/solar_hijri::Aban/solar_hijri::Doshanbe[5],
+    solar_hijri::year{962}/solar_hijri::Azar/solar_hijri::Seshanbe[1],
+    solar_hijri::year{962}/solar_hijri::Azar/solar_hijri::Seshanbe[3],
+    solar_hijri::year{970}/solar_hijri::Dey/solar_hijri::Panjshanbe[1],
+    solar_hijri::year{995}/solar_hijri::Mehr/solar_hijri::Panjshanbe[5],
+    solar_hijri::year{998}/solar_hijri::Mehr/solar_hijri::Yekshanbe[3],
+    solar_hijri::year{1006}/solar_hijri::Mordad/solar_hijri::Doshanbe[3],
+    solar_hijri::year{1028}/solar_hijri::Mehr/solar_hijri::Adine[4],
+    solar_hijri::year{1036}/solar_hijri::Mordad/solar_hijri::Panjshanbe[3],
+    solar_hijri::year{1061}/solar_hijri::Tir/solar_hijri::Seshanbe[1],
+    solar_hijri::year{1070}/solar_hijri::Mehr/solar_hijri::Adine[3],
+    solar_hijri::year{1091}/solar_hijri::Shahrivar/solar_hijri::Seshanbe[4],
+    solar_hijri::year{1097}/solar_hijri::Tir/solar_hijri::Yekshanbe[4],
+    solar_hijri::year{1125}/solar_hijri::Dey/solar_hijri::Chaharshanbe[2],
+    solar_hijri::year{1134}/solar_hijri::Dey/solar_hijri::Panjshanbe[2],
+    solar_hijri::year{1148}/solar_hijri::Dey/solar_hijri::Doshanbe[4],
+    solar_hijri::year{1177}/solar_hijri::Aban/solar_hijri::Chaharshanbe[1],
+    solar_hijri::year{1188}/solar_hijri::Tir/solar_hijri::Seshanbe[3],
+    solar_hijri::year{1213}/solar_hijri::Tir/solar_hijri::Panjshanbe[4],
+    solar_hijri::year{1229}/solar_hijri::Shahrivar/solar_hijri::Doshanbe[3],
+    solar_hijri::year{1244}/solar_hijri::Aban/solar_hijri::Shanbe[2],
+    solar_hijri::year{1281}/solar_hijri::Azar/solar_hijri::Yekshanbe[5],
+    solar_hijri::year{1304}/solar_hijri::Esfand/solar_hijri::Yekshanbe[5],
+    solar_hijri::year{1305}/solar_hijri::Farvardin/solar_hijri::Doshanbe[1],
+    solar_hijri::year{1336}/solar_hijri::Khordad/solar_hijri::Shanbe[2],
+    solar_hijri::year{1355}/solar_hijri::Esfand/solar_hijri::Doshanbe[3],
+    solar_hijri::year{1361}/solar_hijri::Khordad/solar_hijri::Yekshanbe[2],
+    solar_hijri::year{1371}/solar_hijri::Azar/solar_hijri::Seshanbe[3]
+  };
+
+  bool leaps[] = {
+    true,
+    true,
+    true,
+    true,
+    true,
+    false,
+    false,
+    true,
+    true,
+    true,
+    false,
+    false,
+    false,
+    false,
+    false,
+    true,
+    false,
+    false,
+    false,
+    false,
+    false,
+    false,
+    true,
+    false,
+    false,
+    false,
+    false,
+    false
+  };
+
+  static_assert(sizeof(ymdd)/sizeof(ymdd[0]) == sizeof(ymdwd)/sizeof(ymdwd[0]), "");
+  static_assert(sizeof(ymdd)/sizeof(ymdd[0]) == sizeof(ymdh)/sizeof(ymdh[0]), "");
+  static_assert(sizeof(ymdd)/sizeof(ymdd[0]) == sizeof(leaps)/sizeof(leaps[0]), "");
+
+  for (auto i = 0; i < sizeof(ymdd)/sizeof(ymdd[0]); ++i)
+  {
+    assert(solar_hijri::year_month_day{ymdd[i]} == ymdh[i]);
+    assert(ymdd[i] == date::year_month_day{ymdh[i]});
+    assert(ymdh[i].year().is_leap() == leaps[i]);
+    assert(solar_hijri::year_month_weekday{ymdd[i]} == ymdwd[i]);
+  }
+}
+
+int
+main()
+{
+  test_a();
+  test_b();
+  test_c();
+  test_d();
+  test_e();
+  test_f();
+  test_g();
+}
diff --git a/third_party/date-3.0.1/test/solar_hijri_test/year_month_day.pass.cpp b/third_party/date-3.0.1/test/solar_hijri_test/year_month_day.pass.cpp
new file mode 100644
index 00000000..5429314f
--- /dev/null
+++ b/third_party/date-3.0.1/test/solar_hijri_test/year_month_day.pass.cpp
@@ -0,0 +1,168 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2020 Asad. Gharighi
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// class year_month_day
+// {
+// public:
+//     constexpr year_month_day(const date::year& y, const date::month& m,
+//                                const date::day& d) noexcept;
+//     constexpr year_month_day(const year_month_day_last& ymdl) noexcept;
+//     constexpr year_month_day(const sys_days& dp) noexcept;
+//
+//     year_month_day& operator+=(const months& m) noexcept;
+//     year_month_day& operator-=(const months& m) noexcept;
+//     year_month_day& operator+=(const years& y)  noexcept;
+//     year_month_day& operator-=(const years& y)  noexcept;
+//
+//     constexpr date::year  year()  const noexcept;
+//     constexpr date::month month() const noexcept;
+//     constexpr date::day   day()   const noexcept;
+//
+//     constexpr operator sys_days() const noexcept;
+//     constexpr bool ok() const noexcept;
+// };
+
+// constexpr bool operator==(const year_month_day& x, const year_month_day& y) noexcept;
+// constexpr bool operator!=(const year_month_day& x, const year_month_day& y) noexcept;
+// constexpr bool operator< (const year_month_day& x, const year_month_day& y) noexcept;
+// constexpr bool operator> (const year_month_day& x, const year_month_day& y) noexcept;
+// constexpr bool operator<=(const year_month_day& x, const year_month_day& y) noexcept;
+// constexpr bool operator>=(const year_month_day& x, const year_month_day& y) noexcept;
+
+// constexpr year_month_day operator+(const year_month_day& ymd, const months& dm) noexcept;
+// constexpr year_month_day operator+(const months& dm, const year_month_day& ymd) noexcept;
+// constexpr year_month_day operator-(const year_month_day& ymd, const months& dm) noexcept;
+// constexpr year_month_day operator+(const year_month_day& ymd, const years& dy)  noexcept;
+// constexpr year_month_day operator+(const years& dy, const year_month_day& ymd)  noexcept;
+// constexpr year_month_day operator-(const year_month_day& ymd, const years& dy)  noexcept;
+
+// std::ostream& operator<<(std::ostream& os, const year_month_day& ymd);
+
+#include "date.h"
+#include "solar_hijri.h"
+
+#include <iostream>
+#include <cassert>
+#include <sstream>
+#include <type_traits>
+
+static_assert( std::is_trivially_destructible<solar_hijri::year_month_day>{}, "");
+static_assert( std::is_default_constructible<solar_hijri::year_month_day>{}, "");
+static_assert( std::is_trivially_copy_constructible<solar_hijri::year_month_day>{}, "");
+static_assert( std::is_trivially_copy_assignable<solar_hijri::year_month_day>{}, "");
+static_assert( std::is_trivially_move_constructible<solar_hijri::year_month_day>{}, "");
+static_assert( std::is_trivially_move_assignable<solar_hijri::year_month_day>{}, "");
+
+static_assert(std::is_nothrow_constructible<solar_hijri::year_month_day, solar_hijri::year,
+                                                                  solar_hijri::month,
+                                                                  solar_hijri::day>{}, "");
+static_assert(std::is_nothrow_constructible<solar_hijri::year_month_day,
+                                            solar_hijri::year_month_day_last>{}, "");
+static_assert(std::is_convertible<solar_hijri::year_month_day_last, solar_hijri::year_month_day>{}, "");
+static_assert(std::is_nothrow_constructible<solar_hijri::year_month_day, solar_hijri::sys_days>{}, "");
+static_assert(std::is_convertible<solar_hijri::sys_days, solar_hijri::year_month_day>{}, "");
+static_assert(std::is_nothrow_constructible<solar_hijri::sys_days, solar_hijri::year_month_day>{}, "");
+static_assert(std::is_convertible<solar_hijri::year_month_day, solar_hijri::sys_days>{}, "");
+
+void
+test_arithmetic()
+{
+    using namespace solar_hijri;
+
+    for (int y1 = 1380; y1 <= 1400; ++y1)
+    {
+        for (unsigned m1 = 1; m1 <= 12; ++m1)
+        {
+            year_month_day ymd1{year{y1}, month{m1}, 9_d};
+            year_month_day ymd2 = ymd1 + months(24);
+            assert((ymd2 == year_month_day{year{y1+2}, ymd1.month(), ymd1.day()}));
+            ymd2 = ymd1 - months(24);
+            assert((ymd2 == year_month_day{year{y1-2}, ymd1.month(), ymd1.day()}));
+            for (int m2 = -24; m2 <= 24; ++m2)
+            {
+                months m{m2};
+                year_month_day ymd3 = ymd1 + m;
+                months dm = year_month{ymd3.year(), ymd3.month()} -
+                            year_month{ymd2.year(), ymd2.month()};
+                assert(dm == m + years{2});
+                assert(ymd3 - m == ymd1);
+                assert(ymd3 + -m == ymd1);
+                assert(-m + ymd3 == ymd1);
+                assert((year_month_day{ymd1} += m) == ymd3);
+                assert((year_month_day{ymd3} -= m) == ymd1);
+            }
+            for (int y2 = -2; y2 <= 5; ++y2)
+            {
+                years y{y2};
+                year_month_day ymd3 = ymd1 + y;
+                years dy = date::floor<years>(year_month{ymd3.year(), ymd3.month()} -
+                                        year_month{ymd2.year(), ymd2.month()});
+                assert(dy == y + years{2});
+                assert(ymd3 - y == ymd1);
+                assert(ymd3 + -y == ymd1);
+                assert(-y + ymd3 == ymd1);
+                assert((year_month_day{ymd1} += y) == ymd3);
+                assert((year_month_day{ymd3} -= y) == ymd1);
+            }
+        }
+    }
+}
+
+void
+test_day_point_conversion()
+{
+    using namespace solar_hijri;
+    year y   = year{-30000};
+    year end =       30000_y;
+    sys_days prev_dp = sys_days(year_month_day{y, far, 1_d}) - days{1};
+    weekday  prev_wd = weekday{prev_dp};
+    for (; y <= end; ++y)
+    {
+        month m = far;
+        do
+        {
+            day last_day = year_month_day_last{y, month_day_last{m}}.day();
+            for (day d = 1_d; d <= last_day; ++d)
+            {
+                year_month_day ymd = {y, m, d};
+                assert(ymd.ok());
+                sys_days dp = sys_days(ymd);
+                assert(dp == prev_dp + days{1});
+                year_month_day ymd2 = dp;
+                assert(ymd2 == ymd);
+                weekday wd = dp;
+                assert(wd.ok());
+                assert(wd == prev_wd + days{1});
+                prev_wd = wd;
+                prev_dp = dp;
+            }
+        } while (++m != far);
+    }
+}
+
+int
+main()
+{
+  test_arithmetic();
+  test_day_point_conversion();
+}
diff --git a/third_party/date-3.0.1/test/testit b/third_party/date-3.0.1/test/testit
new file mode 100644
index 00000000..21ec3a23
--- /dev/null
+++ b/third_party/date-3.0.1/test/testit
@@ -0,0 +1,177 @@
+#!/bin/sh
+# The MIT License (MIT)
+#
+# Copyright (c) 2015, 2016 Howard Hinnant
+#
+# Permission is hereby granted, free of charge, to any person obtaining a copy
+# of this software and associated documentation files (the "Software"), to deal
+# in the Software without restriction, including without limitation the rights
+# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+# copies of the Software, and to permit persons to whom the Software is
+# furnished to do so, subject to the following conditions:
+#
+# The above copyright notice and this permission notice shall be included in all
+# copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+# SOFTWARE.
+
+currentpath=`pwd`
+origpath=$currentpath
+currentdir=`basename $currentpath`
+while [ $currentdir != "test" ]; do
+	if [ $currentdir = "/" ]
+	then
+		echo "current directory must be in or under \"test\"."
+		exit 1
+	fi
+	cd ..
+	currentpath=`pwd`
+	currentdir=`basename $currentpath`
+done
+
+cd ..
+ROOT=`pwd`
+cd $origpath
+
+if [ -z "$CXX" ]
+then
+	CXX=clang++
+fi
+
+if [ -z "$CXX_LANG" ]
+then
+    CXX_LANG=c++14
+fi
+OPTIONS="-std=${CXX_LANG} $OPTIONS -I$ROOT -Wall $ROOT/src/tz.cpp -lcurl"
+
+echo $ROOT
+HEADER_INCLUDE="-I$ROOT/include -I$ROOT/include/date"
+
+case $TRIPLE in
+  *-*-mingw* | *-*-cygwin* | *-*-win*)
+	TEST_EXE=test.exe
+    ;;
+  *)
+    TEST_EXE=a.out
+    ;;
+esac
+
+case $(uname -s) in
+   NetBSD)
+     THREAD_FLAGS=-lpthread
+     ;;
+esac
+
+FAIL=0
+PASS=0
+UNIMPLEMENTED=0
+IMPLEMENTED_FAIL=0
+IMPLEMENTED_PASS=0
+
+afunc() {
+	fail=0
+	pass=0
+	if (ls ${TEST_PREFIX}*fail.cpp > /dev/null 2>&1)
+	then
+		for FILE in $(ls ${TEST_PREFIX}*fail.cpp); do
+			if $CXX $OPTIONS $HEADER_INCLUDE $SOURCE_LIB $FILE $LIBS -o ./$TEST_EXE > /dev/null 2>&1
+			then
+				rm ./$TEST_EXE
+				echo "$FILE should not compile"
+				fail=$(($fail+1))
+			else
+				pass=$(($pass+1))
+			fi
+		done
+	fi
+
+	if (ls ${TEST_PREFIX}*pass.cpp > /dev/null 2>&1)
+	then
+		for FILE in $(ls ${TEST_PREFIX}*pass.cpp); do
+            if [ "$VERBOSE" ]
+            then
+             	echo "Running test: " $FILE
+            fi
+			if $CXX $OPTIONS $HEADER_INCLUDE $SOURCE_LIB $FILE $LIBS $(test $1 = no || echo $THREAD_FLAGS) -o ./$TEST_EXE
+			then
+				if ./$TEST_EXE
+				then
+					rm ./$TEST_EXE
+					pass=$(($pass+1))
+				else
+					echo "`pwd`/$FILE failed at run time"
+					echo "Compile line was:" $CXX $OPTIONS $HEADER_INCLUDE $SOURCE_LIB $FILE $LIBS $(test $1 = no || echo $THREAD_FLAGS)
+					fail=$(($fail+1))
+					rm ./$TEST_EXE
+				fi
+			else
+				echo "`pwd`/$FILE failed to compile"
+				echo "Compile line was:" $CXX $OPTIONS $HEADER_INCLUDE $SOURCE_LIB $FILE $LIBS $(test $1 = no || echo $THREAD_FLAGS)
+				fail=$(($fail+1))
+			fi
+		done
+	fi
+
+	if [ $fail -gt 0 ]
+	then
+		echo "failed $fail tests in `pwd`"
+		IMPLEMENTED_FAIL=$(($IMPLEMENTED_FAIL+1))
+	fi
+	if [ $pass -gt 0 ]
+	then
+		echo "passed $pass tests in `pwd`"
+		if [ $fail -eq 0 ]
+		then
+			IMPLEMENTED_PASS=$((IMPLEMENTED_PASS+1))
+		fi
+	fi
+	if [ $fail -eq 0 -a $pass -eq 0 ]
+	then
+		echo "not implemented:  `pwd`"
+		UNIMPLEMENTED=$(($UNIMPLEMENTED+1))
+	fi
+
+	FAIL=$(($FAIL+$fail))
+	PASS=$(($PASS+$pass))
+
+	for FILE in *
+	do
+		if [ -d "$FILE" ];
+		then
+			cd $FILE
+			if [ $FILE = thread -o $1 = yes ]; then
+				afunc yes
+			else
+				afunc no
+			fi
+			cd ..
+		fi
+	done
+}
+
+afunc no
+
+echo "****************************************************"
+echo "Results for `pwd`:"
+echo "using `$CXX --version`"
+echo "with $OPTIONS $HEADER_INCLUDE $SOURCE_LIB"
+echo "----------------------------------------------------"
+echo "sections without tests   : $UNIMPLEMENTED"
+echo "sections with failures   : $IMPLEMENTED_FAIL"
+echo "sections without failures: $IMPLEMENTED_PASS"
+echo "                       +   ----"
+echo "total number of sections : $(($UNIMPLEMENTED+$IMPLEMENTED_FAIL+$IMPLEMENTED_PASS))"
+echo "----------------------------------------------------"
+echo "number of tests failed   : $FAIL"
+echo "number of tests passed   : $PASS"
+echo "                       +   ----"
+echo "total number of tests    : $(($FAIL+$PASS))"
+echo "****************************************************"
+
+exit $FAIL
diff --git a/third_party/date-3.0.1/test/tz_test/OffsetZone.h b/third_party/date-3.0.1/test/tz_test/OffsetZone.h
new file mode 100644
index 00000000..bacb03ca
--- /dev/null
+++ b/third_party/date-3.0.1/test/tz_test/OffsetZone.h
@@ -0,0 +1,73 @@
+#ifndef OFFSET_ZONE_H
+#define OFFSET_ZONE_H
+
+// The MIT License (MIT)
+//
+// Copyright (c) 2017 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// Test custom time zone support
+
+#include "tz.h"
+
+class OffsetZone
+{
+    std::chrono::minutes offset_;
+
+public:
+    explicit OffsetZone(std::chrono::minutes offset)
+        : offset_{offset}
+        {}
+
+    template <class Duration>
+        auto
+        to_local(date::sys_time<Duration> tp) const
+        {
+            using namespace date;
+            using namespace std::chrono;
+            using LT = local_time<std::common_type_t<Duration, minutes>>;
+            return LT{(tp + offset_).time_since_epoch()};
+        }
+
+    template <class Duration>
+        auto
+        to_sys(date::local_time<Duration> tp, date::choose = date::choose::earliest) const
+        {
+            using namespace date;
+            using namespace std::chrono;
+            using ST = sys_time<std::common_type_t<Duration, minutes>>;
+            return ST{(tp - offset_).time_since_epoch()};
+        }
+
+    template <class Duration>
+        date::sys_info
+        get_info(date::sys_time<Duration> st) const
+        {
+            using namespace date;
+            using namespace std::chrono;
+            return {sys_seconds::min(), sys_seconds::max(), offset_,
+                    minutes{0}, offset_ >= minutes{0} ? "+" + date::format("%H%M", offset_)
+                                          : "-" + date::format("%H%M", -offset_)};
+        }
+
+    const OffsetZone* operator->() const {return this;}
+};
+
+#endif // OFFSET_ZONE_H
diff --git a/third_party/date-3.0.1/test/tz_test/OffsetZone.pass.cpp b/third_party/date-3.0.1/test/tz_test/OffsetZone.pass.cpp
new file mode 100644
index 00000000..0cef837e
--- /dev/null
+++ b/third_party/date-3.0.1/test/tz_test/OffsetZone.pass.cpp
@@ -0,0 +1,38 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2017 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// Test custom time zone support
+
+#include "tz.h"
+#include "OffsetZone.h"
+#include <cassert>
+
+int
+main()
+{
+    using namespace date;
+    using namespace std::chrono;
+    auto now = system_clock::now();
+    auto offset = hours{-4};
+    zoned_time<system_clock::duration, OffsetZone> zt{OffsetZone{offset}, now};
+    assert(zt.get_local_time().time_since_epoch() == now.time_since_epoch() + offset);
+}
diff --git a/third_party/date-3.0.1/test/tz_test/README.md b/third_party/date-3.0.1/test/tz_test/README.md
new file mode 100644
index 00000000..9a3699ef
--- /dev/null
+++ b/third_party/date-3.0.1/test/tz_test/README.md
@@ -0,0 +1,22 @@
+# TZ Test
+
+## How to Test
+
+* Install tz.cpp by downloading the IANA timezone database at: http://www.iana.org/time-zones You only need the data, not the code.
+* Change the string `install` in tz.cpp to point to your downloaded IANA database.
+* Compile validate.cpp along with tz.cpp.
+* Run the binary and direct the terminal output to a temporary file.
+* Unzip the tzdata file that has the version corresponding to the IANA database you downloaded (e.g. tzdata2015f.txt.zip).
+* Compare the unzipped txt file with the output of your validate test program. If they are identical, the test passes, else it fails.
+
+## Miscellaneous
+
+You can also compare one version of the tzdatabase with another using
+these uncompressed text files.  The text files contain for each
+timezone its initial state, and each {offset, abbreviation} change
+contained in the database up through the year 2035.  As the database
+versions change, minor updates to the set of these transitions are
+typically made, typically due to changes in government policies.
+
+The tests in this section will run much faster with optimizations
+cranked up.
diff --git a/third_party/date-3.0.1/test/tz_test/tzdata2015e.txt.zip b/third_party/date-3.0.1/test/tz_test/tzdata2015e.txt.zip
new file mode 100644
index 00000000..144f7d35
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diff --git a/third_party/date-3.0.1/test/tz_test/tzdata2015f.txt.zip b/third_party/date-3.0.1/test/tz_test/tzdata2015f.txt.zip
new file mode 100644
index 00000000..a102e6c4
Binary files /dev/null and b/third_party/date-3.0.1/test/tz_test/tzdata2015f.txt.zip differ
diff --git a/third_party/date-3.0.1/test/tz_test/tzdata2016c.txt.zip b/third_party/date-3.0.1/test/tz_test/tzdata2016c.txt.zip
new file mode 100644
index 00000000..fcaac054
Binary files /dev/null and b/third_party/date-3.0.1/test/tz_test/tzdata2016c.txt.zip differ
diff --git a/third_party/date-3.0.1/test/tz_test/tzdata2016d.txt.zip b/third_party/date-3.0.1/test/tz_test/tzdata2016d.txt.zip
new file mode 100644
index 00000000..8af5ea15
Binary files /dev/null and b/third_party/date-3.0.1/test/tz_test/tzdata2016d.txt.zip differ
diff --git a/third_party/date-3.0.1/test/tz_test/tzdata2016e.txt.zip b/third_party/date-3.0.1/test/tz_test/tzdata2016e.txt.zip
new file mode 100644
index 00000000..623cfb15
Binary files /dev/null and b/third_party/date-3.0.1/test/tz_test/tzdata2016e.txt.zip differ
diff --git a/third_party/date-3.0.1/test/tz_test/tzdata2016f.txt.zip b/third_party/date-3.0.1/test/tz_test/tzdata2016f.txt.zip
new file mode 100644
index 00000000..e96b5365
Binary files /dev/null and b/third_party/date-3.0.1/test/tz_test/tzdata2016f.txt.zip differ
diff --git a/third_party/date-3.0.1/test/tz_test/tzdb_list.pass.cpp b/third_party/date-3.0.1/test/tz_test/tzdb_list.pass.cpp
new file mode 100644
index 00000000..01de57ef
--- /dev/null
+++ b/third_party/date-3.0.1/test/tz_test/tzdb_list.pass.cpp
@@ -0,0 +1,36 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2020 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+#include "tz.h"
+#include <type_traits>
+
+int
+main()
+{
+    using namespace date;
+    static_assert( std::is_nothrow_destructible<tzdb_list>{}, "");
+    static_assert( std::is_nothrow_default_constructible<tzdb_list>{}, "");
+    static_assert(!std::is_copy_constructible<tzdb_list>{}, "");
+    static_assert(!std::is_copy_assignable<tzdb_list>{}, "");
+    static_assert( std::is_nothrow_move_constructible<tzdb_list>{}, "");
+    static_assert(!std::is_move_assignable<tzdb_list>{}, "");
+}
diff --git a/third_party/date-3.0.1/test/tz_test/validate.cpp b/third_party/date-3.0.1/test/tz_test/validate.cpp
new file mode 100644
index 00000000..2202b378
--- /dev/null
+++ b/third_party/date-3.0.1/test/tz_test/validate.cpp
@@ -0,0 +1,165 @@
+#include "date/tz.h"
+#include <iostream>
+
+void
+test_info(const date::time_zone* zone, const date::sys_info& info)
+{
+    using namespace date;
+    using namespace std::chrono;
+    auto begin = info.begin;
+    auto end = info.end - microseconds{1};
+    auto mid = begin + (end - begin) /2;
+    using sys_microseconds = sys_time<microseconds>;
+    using zoned_microseconds = zoned_time<microseconds>;
+    zoned_microseconds local{zone};
+
+    if (begin > sys_days{jan/1/1700})
+    {
+        auto prev_local = local;
+        local = begin;
+        prev_local = begin - seconds{1};
+        auto slocal = local.get_local_time();
+        auto plocal = prev_local.get_local_time();
+        if (plocal < slocal - seconds{1})
+        {
+            assert(sys_microseconds{local} == begin);
+            try
+            {
+                local = plocal + (slocal - seconds{1} - plocal) / 2;
+                assert(false);
+            }
+            catch (const nonexistent_local_time&)
+            {
+            }
+        }
+        else if (plocal > slocal - seconds{1})
+        {
+            try
+            {
+                local = slocal - seconds{1} + (plocal - (slocal - seconds{1})) / 2;
+                assert(false);
+            }
+            catch (const ambiguous_local_time&)
+            {
+            }
+        }
+    }
+
+    local = mid;
+    assert(sys_microseconds{local} == mid);
+
+    if (end < sys_days{jan/1/3000})
+    {
+        local = end;
+        auto next_local = local;
+        next_local = info.end;
+        auto slocal = local.get_local_time();
+        auto nlocal = next_local.get_local_time();
+        if (nlocal < slocal + microseconds{1})
+        {
+            try
+            {
+                local = nlocal + (slocal + microseconds{1} - nlocal) / 2;
+                assert(false);
+            }
+            catch (const ambiguous_local_time&)
+            {
+            }
+        }
+        else if (nlocal > slocal + microseconds{1})
+        {
+            assert(sys_microseconds{local} == end);
+            try
+            {
+                local = slocal + microseconds{1} +
+                        (nlocal - (slocal + microseconds{1})) / 2;
+                assert(false);
+            }
+            catch (const nonexistent_local_time&)
+            {
+            }
+        }
+    }
+}
+
+void
+tzmain()
+{
+    using namespace date;
+    using namespace std::chrono;
+    auto& db = get_tzdb();
+    std::vector<std::string> names;
+#if USE_OS_TZDB
+    names.reserve(db.zones.size());
+    for (auto& zone : db.zones)
+        names.push_back(zone.name());
+#else  // !USE_OS_TZDB
+    names.reserve(db.zones.size() + db.links.size());
+    for (auto& zone : db.zones)
+        names.push_back(zone.name());
+    for (auto& link : db.links)
+        names.push_back(link.name());
+    std::sort(names.begin(), names.end());
+#endif  // !USE_OS_TZDB
+    std::cout << db.version << "\n\n";
+    for (auto const& name : names)
+    {
+        std::cout << name << '\n';
+        auto z = locate_zone(name);
+        auto begin = sys_days(jan/1/year::min()) + seconds{0};
+        auto end   = sys_days(jan/1/2035) + seconds{0};
+        auto info = z->get_info(begin);
+        std::cout << "Initially:           ";
+        if (info.offset >= seconds{0})
+            std::cout << '+';
+        std::cout << make_time(info.offset);
+        if (info.save == minutes{0})
+            std::cout << " standard ";
+        else
+            std::cout << " daylight ";
+        std::cout << info.abbrev << '\n';
+        test_info(z, info);
+        auto prev_offset = info.offset;
+        auto prev_abbrev = info.abbrev;
+        auto prev_save = info.save;
+        for (begin = info.end; begin < end; begin = info.end)
+        {
+            info = z->get_info(begin);
+            test_info(z, info);
+            if (info.offset == prev_offset && info.abbrev == prev_abbrev &&
+                    info.save == prev_save)
+                continue;
+            auto dp = floor<days>(begin);
+            auto ymd = year_month_day(dp);
+            auto time = make_time(begin - dp);
+            std::cout << ymd << ' ' << time << "Z ";
+            if (info.offset >= seconds{0})
+                std::cout << '+';
+            std::cout << make_time(info.offset);
+            if (info.save == minutes{0})
+                std::cout << " standard ";
+            else
+                std::cout << " daylight ";
+            std::cout << info.abbrev << '\n';
+            prev_offset = info.offset;
+            prev_abbrev = info.abbrev;
+            prev_save = info.save;
+        }
+        std::cout << '\n';
+    }
+}
+
+int
+main()
+{
+    try
+    {
+        tzmain();
+    }
+    catch(const std::exception& ex)
+    {
+        std::cout << "An exception occured: " << ex.what() << std::endl;
+        return EXIT_FAILURE;
+    }
+    return EXIT_SUCCESS;
+}
diff --git a/third_party/date-3.0.1/test/tz_test/zone.pass.cpp b/third_party/date-3.0.1/test/tz_test/zone.pass.cpp
new file mode 100644
index 00000000..a0b003c9
--- /dev/null
+++ b/third_party/date-3.0.1/test/tz_test/zone.pass.cpp
@@ -0,0 +1,37 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2015, 2016 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+#include "tz.h"
+#include <type_traits>
+
+int
+main()
+{
+    using namespace std;
+    using namespace date;
+    static_assert( is_nothrow_destructible<time_zone>{}, "");
+    static_assert(!is_default_constructible<time_zone>{}, "");
+    static_assert(!is_copy_constructible<time_zone>{}, "");
+    static_assert(!is_copy_assignable<time_zone>{}, "");
+    static_assert( is_nothrow_move_constructible<time_zone>{}, "");
+    static_assert( is_nothrow_move_assignable<time_zone>{}, "");
+}
diff --git a/third_party/date-3.0.1/test/tz_test/zoned_time.pass.cpp b/third_party/date-3.0.1/test/tz_test/zoned_time.pass.cpp
new file mode 100644
index 00000000..70f3a83e
--- /dev/null
+++ b/third_party/date-3.0.1/test/tz_test/zoned_time.pass.cpp
@@ -0,0 +1,464 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2017 Howard Hinnant
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+// template <class Duration>
+// class zoned_time
+// {
+// public:
+//     using duration = typename std::common_type<Duration, std::chrono::seconds>::type;
+// 
+//              zoned_time();
+//              zoned_time(const sys_time<Duration>& st);
+//     explicit zoned_time(const time_zone* z);
+//     explicit zoned_time(std::string_view name);
+// 
+//     template <class Duration2,
+//               class = typename std::enable_if
+//                       <
+//                           std::is_convertible<sys_time<Duration2>,
+//                                               sys_time<Duration>>::value
+//                       >::type>
+//         zoned_time(const zoned_time<Duration2>& zt) NOEXCEPT;
+// 
+//     zoned_time(const time_zone* z,    const local_time<Duration>& tp);
+//     zoned_time(std::string_view name, const local_time<Duration>& tp);
+//     zoned_time(const time_zone* z,    const local_time<Duration>& tp, choose c);
+//     zoned_time(std::string_view name, const local_time<Duration>& tp, choose c);
+// 
+//     zoned_time(const time_zone* z,    const zoned_time<Duration>& zt);
+//     zoned_time(std::string_view name, const zoned_time<Duration>& zt);
+//     zoned_time(const time_zone* z,    const zoned_time<Duration>& zt, choose);
+//     zoned_time(std::string_view name, const zoned_time<Duration>& zt, choose);
+// 
+//     zoned_time(const time_zone* z,    const sys_time<Duration>& st);
+//     zoned_time(std::string_view name, const sys_time<Duration>& st);
+// 
+//     zoned_time& operator=(const sys_time<Duration>& st);
+//     zoned_time& operator=(const local_time<Duration>& ut);
+// 
+//     explicit operator sys_time<duration>() const;
+//     explicit operator local_time<duration>() const;
+// 
+//     const time_zone*     get_time_zone() const;
+//     local_time<duration> get_local_time() const;
+//     sys_time<duration>   get_sys_time() const;
+//     sys_info             get_info() const;
+// 
+//     template <class Duration1, class Duration2>
+//     friend
+//     bool
+//     operator==(const zoned_time<Duration1>& x, const zoned_time<Duration2>& y);
+// 
+//     template <class CharT, class Traits, class Duration1>
+//     friend
+//     std::basic_ostream<CharT, Traits>&
+//     operator<<(std::basic_ostream<CharT, Traits>& os, const zoned_time<Duration1>& t);
+// };
+//
+// using zoned_seconds = zoned_time<std::chrono::seconds>;
+//
+// template <class Duration1, class Duration2>
+// inline
+// bool
+// operator!=(const zoned_time<Duration1>& x, const zoned_time<Duration2>& y);
+//
+// template <class Duration>
+// zoned_time(sys_time<Duration>)
+//     -> zoned_time<std::common_type_t<Duration, std::chrono::seconds>>;
+//
+// template <class Zone, class Duration>
+// zoned_time(Zone, sys_time<Duration>)
+//     -> zoned_time<std::common_type_t<Duration, std::chrono::seconds>>;
+//
+// template <class Zone, class Duration>
+// zoned_time(Zone, local_time<Duration>, choose = choose::earliest)
+//     -> zoned_time<std::common_type_t<Duration, std::chrono::seconds>>;
+//
+// template <class Zone, class Duration>
+// zoned_time(Zone, zoned_time<Duration>, choose = choose::earliest)
+//     -> zoned_time<std::common_type_t<Duration, std::chrono::seconds>>;
+
+#include "tz.h"
+#include <cassert>
+#include <sstream>
+#include <type_traits>
+
+int
+main()
+{
+    using namespace std;
+    using namespace std::chrono;
+    using namespace date;
+    static_assert( is_nothrow_destructible<zoned_seconds>{}, "");
+    static_assert( is_default_constructible<zoned_seconds>{}, "");
+    static_assert( is_nothrow_copy_constructible<zoned_seconds>{}, "");
+    static_assert( is_nothrow_copy_assignable<zoned_seconds>{}, "");
+    static_assert( is_nothrow_move_constructible<zoned_seconds>{}, "");
+    static_assert( is_nothrow_move_assignable<zoned_seconds>{}, "");
+
+    static_assert(is_same<zoned_time<minutes>::duration, seconds>{}, "");
+    static_assert(is_same<zoned_seconds::duration, seconds>{}, "");
+    static_assert(is_same<zoned_time<milliseconds>::duration, milliseconds>{}, "");
+
+    // zoned_time();
+    {
+        zoned_seconds zt;
+        assert(zt.get_sys_time() == sys_seconds{});
+        assert(zt.get_time_zone()->name() == "Etc/UTC");
+    }
+
+    // zoned_time(const sys_time<Duration>& st);
+    {
+        static_assert(!is_convertible<sys_days, zoned_seconds>{}, "");
+        static_assert( is_constructible<zoned_seconds, sys_days>{}, "");
+        static_assert( is_convertible<sys_seconds, zoned_seconds>{}, "");
+        static_assert(!is_convertible<sys_time<milliseconds>, zoned_seconds>{}, "");
+        static_assert(!is_constructible<zoned_seconds, sys_time<milliseconds>>{}, "");
+
+        auto now = floor<seconds>(system_clock::now());
+        zoned_seconds zt = now;
+        assert(zt.get_sys_time() == now);
+        assert(zt.get_time_zone()->name() == "Etc/UTC");
+    }
+
+    // explicit zoned_time(const time_zone* z);
+    {
+        static_assert(!is_convertible<const time_zone*, zoned_seconds>{}, "");
+        static_assert( is_constructible<zoned_seconds, const time_zone*>{}, "");
+        zoned_seconds zt{locate_zone("America/New_York")};
+        assert(zt.get_sys_time() == sys_seconds{});
+        assert(zt.get_time_zone()->name() == "America/New_York");
+    }
+
+    // explicit zoned_time(std::string_view name);
+    {
+        static_assert(!is_convertible<std::string, zoned_seconds>{}, "");
+        static_assert( is_constructible<zoned_seconds, std::string>{}, "");
+        static_assert( is_constructible<zoned_seconds, const char*>{}, "");
+        static_assert( is_constructible<zoned_seconds, const char[3]>{}, "");
+        zoned_seconds zt{"America/New_York"};
+        assert(zt.get_sys_time() == sys_seconds{});
+        assert(zt.get_time_zone()->name() == "America/New_York");
+    }
+
+    // template <class Duration2,
+    //           class = typename std::enable_if
+    //                   <
+    //                       std::is_convertible<sys_time<Duration2>,
+    //                                           sys_time<Duration>>::value
+    //                   >::type>
+    //     zoned_time(const zoned_time<Duration2>& zt) NOEXCEPT;
+    {
+        static_assert( is_convertible<zoned_time<days>, zoned_seconds>{}, "");
+        static_assert(!is_constructible<zoned_time<days>, zoned_seconds>{}, "");
+        zoned_time<days> zt1{"America/New_York", sys_days{2017_y/jul/5}};
+        zoned_seconds zt2 = zt1;
+        assert(zt2.get_sys_time() == sys_days{2017_y/jul/5});
+        assert(zt2.get_time_zone()->name() == "America/New_York");
+    }
+
+    // zoned_time(const time_zone* z, const local_time<Duration>& tp);
+    {
+        static_assert( is_constructible<zoned_seconds, const time_zone*, local_days>{}, "");
+        zoned_seconds zt = {locate_zone("America/New_York"), local_days{2017_y/jul/5}};
+        assert(zt.get_local_time() == local_days{2017_y/jul/5});
+        assert(zt.get_time_zone()->name() == "America/New_York");
+        try
+        {
+            zoned_seconds zt1 = {locate_zone("America/New_York"),
+                                 local_days{2017_y/mar/sun[2]} + hours{2} + minutes{15}};
+            assert(false);
+        }
+        catch(const nonexistent_local_time&)
+        {
+        }
+        try
+        {
+            zoned_seconds zt1 = {locate_zone("America/New_York"),
+                                 local_days{2017_y/nov/sun[1]} + hours{1} + minutes{15}};
+            assert(false);
+        }
+        catch(const ambiguous_local_time&)
+        {
+        }
+    }
+
+    // zoned_time(std::string_view name, const local_time<Duration>& tp);
+    {
+        static_assert( is_constructible<zoned_seconds, std::string, local_days>{}, "");
+        static_assert( is_constructible<zoned_seconds, const char*, local_days>{}, "");
+        zoned_seconds zt = {"America/New_York", local_days{2017_y/jul/5}};
+        assert(zt.get_local_time() == local_days{2017_y/jul/5});
+        assert(zt.get_time_zone()->name() == "America/New_York");
+        try
+        {
+            zoned_seconds zt1 = {"America/New_York",
+                                 local_days{2017_y/mar/sun[2]} + hours{2} + minutes{15}};
+            assert(false);
+        }
+        catch(const nonexistent_local_time&)
+        {
+        }
+        try
+        {
+            zoned_seconds zt1 = {"America/New_York",
+                                 local_days{2017_y/nov/sun[1]} + hours{1} + minutes{15}};
+            assert(false);
+        }
+        catch(const ambiguous_local_time&)
+        {
+        }
+    }
+
+    // zoned_time(const time_zone* z, const local_time<Duration>& tp, choose c);
+    {
+        static_assert( is_constructible<zoned_seconds, const time_zone*, local_days, choose>{}, "");
+        zoned_seconds zt = {locate_zone("America/New_York"),
+                            local_days{2017_y/jul/5} + hours{2} + minutes{15},
+                            choose::earliest};
+        assert(zt.get_sys_time() == sys_days{2017_y/jul/5} + hours{6} + minutes{15});
+        assert(zt.get_time_zone()->name() == "America/New_York");
+
+        zt = {locate_zone("America/New_York"),
+                            local_days{2017_y/jul/5} + hours{2} + minutes{15},
+                            choose::latest};
+        assert(zt.get_sys_time() == sys_days{2017_y/jul/5} + hours{6} + minutes{15});
+        assert(zt.get_time_zone()->name() == "America/New_York");
+
+        static_assert( is_constructible<zoned_seconds, const time_zone*, local_days, choose>{}, "");
+        zoned_seconds zt1 = {locate_zone("America/New_York"),
+                             local_days{2017_y/mar/sun[2]} + hours{2} + minutes{15},
+                             choose::earliest};
+        assert(zt1.get_sys_time() == sys_days{2017_y/mar/12} + hours{7});
+        assert(zt1.get_time_zone()->name() == "America/New_York");
+
+        zoned_seconds zt2 = {locate_zone("America/New_York"),
+                             local_days{2017_y/mar/sun[2]} + hours{2} + minutes{15},
+                             choose::latest};
+        assert(zt2.get_sys_time() == sys_days{2017_y/mar/12} + hours{7});
+        assert(zt2.get_time_zone()->name() == "America/New_York");
+
+        zoned_seconds zt3 = {locate_zone("America/New_York"),
+                             local_days{2017_y/nov/sun[1]} + hours{1} + minutes{15},
+                             choose::earliest};
+        assert(zt3.get_sys_time() == sys_days{2017_y/nov/5} + hours{5} + minutes{15});
+        assert(zt3.get_time_zone()->name() == "America/New_York");
+
+        zoned_seconds zt4 = {locate_zone("America/New_York"),
+                             local_days{2017_y/nov/sun[1]} + hours{1} + minutes{15},
+                             choose::latest};
+        assert(zt4.get_sys_time() == sys_days{2017_y/nov/5} + hours{6} + minutes{15});
+        assert(zt4.get_time_zone()->name() == "America/New_York");
+    }
+
+    // zoned_time(std::string_view name, const local_time<Duration>& tp, choose c);
+    {
+        static_assert( is_constructible<zoned_seconds, std::string, local_days, choose>{}, "");
+        static_assert( is_constructible<zoned_seconds, const char*, local_days, choose>{}, "");
+        zoned_seconds zt = {"America/New_York",
+                            local_days{2017_y/jul/5} + hours{2} + minutes{15},
+                            choose::earliest};
+        assert(zt.get_sys_time() == sys_days{2017_y/jul/5} + hours{6} + minutes{15});
+        assert(zt.get_time_zone()->name() == "America/New_York");
+
+        zt = {"America/New_York",
+                            local_days{2017_y/jul/5} + hours{2} + minutes{15},
+                            choose::latest};
+        assert(zt.get_sys_time() == sys_days{2017_y/jul/5} + hours{6} + minutes{15});
+        assert(zt.get_time_zone()->name() == "America/New_York");
+
+        static_assert( is_constructible<zoned_seconds, const time_zone*, local_days, choose>{}, "");
+        zoned_seconds zt1 = {"America/New_York",
+                             local_days{2017_y/mar/sun[2]} + hours{2} + minutes{15},
+                             choose::earliest};
+        assert(zt1.get_sys_time() == sys_days{2017_y/mar/12} + hours{7});
+        assert(zt1.get_time_zone()->name() == "America/New_York");
+
+        zoned_seconds zt2 = {"America/New_York",
+                             local_days{2017_y/mar/sun[2]} + hours{2} + minutes{15},
+                             choose::latest};
+        assert(zt2.get_sys_time() == sys_days{2017_y/mar/12} + hours{7});
+        assert(zt2.get_time_zone()->name() == "America/New_York");
+
+        zoned_seconds zt3 = {"America/New_York",
+                             local_days{2017_y/nov/sun[1]} + hours{1} + minutes{15},
+                             choose::earliest};
+        assert(zt3.get_sys_time() == sys_days{2017_y/nov/5} + hours{5} + minutes{15});
+        assert(zt3.get_time_zone()->name() == "America/New_York");
+
+        zoned_seconds zt4 = {"America/New_York",
+                             local_days{2017_y/nov/sun[1]} + hours{1} + minutes{15},
+                             choose::latest};
+        assert(zt4.get_sys_time() == sys_days{2017_y/nov/5} + hours{6} + minutes{15});
+        assert(zt4.get_time_zone()->name() == "America/New_York");
+    }
+
+    // zoned_time(const time_zone* z, const sys_time<Duration>& st);
+    {
+        static_assert( is_constructible<zoned_seconds, const time_zone*, sys_days>{}, "");
+
+        zoned_seconds zt = {locate_zone("America/New_York"),
+                            sys_days{2017_y/jul/5} + hours{2} + minutes{15}};
+        assert(zt.get_sys_time() == sys_days{2017_y/jul/5} + hours{2} + minutes{15});
+        assert(zt.get_time_zone()->name() == "America/New_York");
+    }
+
+    // zoned_time(std::string_view name, const sys_time<Duration>& st);
+    {
+        static_assert( is_constructible<zoned_seconds, std::string, sys_days>{}, "");
+        static_assert( is_constructible<zoned_seconds, const char*, sys_days>{}, "");
+
+        zoned_seconds zt = {"America/New_York",
+                            sys_days{2017_y/jul/5} + hours{2} + minutes{15}};
+        assert(zt.get_sys_time() == sys_days{2017_y/jul/5} + hours{2} + minutes{15});
+        assert(zt.get_time_zone()->name() == "America/New_York");
+    }
+
+    // zoned_time& operator=(const sys_time<Duration>& st);
+    {
+        static_assert( is_assignable<zoned_seconds, const sys_days&>{}, "");
+
+        zoned_seconds zt{"America/New_York"};
+        zt = sys_days{2017_y/jul/5};
+        assert(zt.get_sys_time() == sys_days{2017_y/jul/5});
+        assert(zt.get_time_zone()->name() == "America/New_York");
+    }
+
+    // zoned_time& operator=(const local_time<Duration>& st);
+    {
+        static_assert( is_assignable<zoned_seconds, const local_days&>{}, "");
+
+        zoned_seconds zt{"America/New_York"};
+        zt = local_days{2017_y/jul/5};
+        assert(zt.get_local_time() == local_days{2017_y/jul/5});
+        assert(zt.get_time_zone()->name() == "America/New_York");
+        try
+        {
+            zt = {"America/New_York",
+                                 local_days{2017_y/mar/sun[2]} + hours{2} + minutes{15}};
+            assert(false);
+        }
+        catch(const nonexistent_local_time&)
+        {
+            assert(zt.get_local_time() == local_days{2017_y/jul/5});
+            assert(zt.get_time_zone()->name() == "America/New_York");
+        }
+        try
+        {
+            zt = {"America/New_York",
+                                 local_days{2017_y/nov/sun[1]} + hours{1} + minutes{15}};
+            assert(false);
+        }
+        catch(const ambiguous_local_time&)
+        {
+            assert(zt.get_local_time() == local_days{2017_y/jul/5});
+            assert(zt.get_time_zone()->name() == "America/New_York");
+        }
+    }
+
+    // explicit operator sys_time<duration>() const;
+    {
+        static_assert(!is_convertible<zoned_seconds, sys_seconds>{}, "");
+        static_assert( is_constructible<sys_seconds, zoned_seconds>{}, "");
+        auto now = floor<seconds>(system_clock::now());
+        const zoned_seconds zt = {"America/New_York", now};
+        assert(sys_seconds{zt} == now);
+    }
+
+    // explicit operator local_time<duration>() const;
+    {
+        static_assert(!is_convertible<zoned_seconds, local_seconds>{}, "");
+        static_assert( is_constructible<local_seconds, zoned_seconds>{}, "");
+        auto now = local_days{2017_y/jul/5} + hours{23} + minutes{1} + seconds{48};
+        const zoned_seconds zt = {"America/New_York", now};
+        assert(local_seconds{zt} == now);
+    }
+
+    // const time_zone* get_time_zone() const;
+    {
+        const zoned_seconds zt{"America/New_York"};
+        assert(zt.get_time_zone() == locate_zone("America/New_York"));
+    }
+
+    // local_time<duration> get_local_time() const;
+    {
+        const zoned_seconds zt{"America/New_York", sys_days{2017_y/jul/6} +
+                                                   hours{3} + minutes{7} + seconds{9}};
+        assert(zt.get_local_time() == local_days{2017_y/jul/5} +
+                                      hours{23} + minutes{7} + seconds{9});
+    }
+
+    // sys_time<duration> get_sys_time() const;
+    {
+        const zoned_seconds zt{"America/New_York", sys_days{2017_y/jul/6} +
+                                                   hours{3} + minutes{7} + seconds{9}};
+        assert(zt.get_sys_time() == sys_days{2017_y/jul/6} +
+                                    hours{3} + minutes{7} + seconds{9});
+    }
+
+    // sys_info get_info() const;
+    {
+        const zoned_seconds zt{"America/New_York", sys_days{2017_y/jul/6} +
+                                                   hours{3} + minutes{7} + seconds{9}};
+        auto info = zt.get_info();
+        assert(info.begin == sys_days{2017_y/mar/12} + hours{7});
+        assert(info.end == sys_days{2017_y/nov/5} + hours{6});
+        assert(info.offset == hours{-4});
+        assert(info.save != minutes{0});
+        assert(info.abbrev == "EDT");
+    }
+
+    // template <class Duration1, class Duration2>
+    // bool
+    // operator==(const zoned_time<Duration1>& x, const zoned_time<Duration2>& y);
+    {
+        const zoned_seconds zt{"America/New_York", sys_days{2017_y/jul/6} +
+                                                   hours{3} + minutes{7} + seconds{9}};
+        const zoned_seconds zt1{"America/New_York", sys_days{2017_y/jul/6} +
+                                                   hours{3} + minutes{7} + seconds{10}};
+        assert(zt == zt);
+        assert(!(zt == zt1));
+    }
+
+    // template <class Duration1, class Duration2>
+    // bool
+    // operator!=(const zoned_time<Duration1>& x, const zoned_time<Duration2>& y);
+    {
+        const zoned_seconds zt{"America/New_York", sys_days{2017_y/jul/6} +
+                                                   hours{3} + minutes{7} + seconds{9}};
+        const zoned_seconds zt1{"America/New_York", sys_days{2017_y/jul/6} +
+                                                   hours{3} + minutes{7} + seconds{10}};
+        assert(!(zt != zt));
+        assert(zt != zt1);
+    }
+
+    // template <class CharT, class Traits, class Duration1>
+    // std::basic_ostream<CharT, Traits>&
+    // operator<<(std::basic_ostream<CharT, Traits>& os, const zoned_time<Duration1>& t);
+    {
+        const zoned_seconds zt{"America/New_York", sys_days{2017_y/jul/6} +
+                                                   hours{3} + minutes{7} + seconds{9}};
+        std::ostringstream test;
+        test << zt;
+        assert(test.str() == "2017-07-05 23:07:09 EDT");
+    }
+}
diff --git a/third_party/date-3.0.1/test/tz_test/zoned_time_deduction.pass.cpp b/third_party/date-3.0.1/test/tz_test/zoned_time_deduction.pass.cpp
new file mode 100644
index 00000000..e62e11aa
--- /dev/null
+++ b/third_party/date-3.0.1/test/tz_test/zoned_time_deduction.pass.cpp
@@ -0,0 +1,246 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2019 Tomasz Kamiński
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+#include "tz.h"
+#include "OffsetZone.h"
+#include <cassert>
+#include <type_traits>
+#include <string>
+
+#if HAS_DEDUCTION_GUIDES
+#include <string_view>
+
+template<typename TimeZonePtr, typename Source>
+void testDeductionFrom(Source&& s)
+{
+    using namespace date;
+    using namespace std::chrono;
+
+    // No time point
+    {
+        zoned_time zt(std::forward<Source>(s));
+        static_assert(std::is_same<decltype(zt), zoned_time<seconds, TimeZonePtr>>::value, "");
+    }
+
+    // sys_time
+    {
+        sys_days sd(2017_y/feb/20);
+        zoned_time ztd(std::forward<Source>(s), sd);
+        static_assert(std::is_same<decltype(ztd), zoned_time<seconds, TimeZonePtr>>::value, "");
+
+        sys_time<seconds> ss(sd);
+        zoned_time zts(std::forward<Source>(s), ss);
+        static_assert(std::is_same<decltype(zts), zoned_time<seconds, TimeZonePtr>>::value, "");
+
+        sys_time<milliseconds> sms(ss);
+        zoned_time ztms(std::forward<Source>(s), sms);
+        static_assert(std::is_same<decltype(ztms), zoned_time<milliseconds, TimeZonePtr>>::value, "");
+    }
+
+    // local_time
+    {
+        local_days ld(2017_y/feb/20);
+        zoned_time ztd(std::forward<Source>(s), ld);
+        static_assert(std::is_same<decltype(ztd), zoned_time<seconds, TimeZonePtr>>::value, "");
+
+        local_time<seconds> ls(ld);
+        zoned_time zts(std::forward<Source>(s), ls);
+        static_assert(std::is_same<decltype(zts), zoned_time<seconds, TimeZonePtr>>::value, "");
+
+        local_time<milliseconds> lms(ls);
+        zoned_time ztms(std::forward<Source>(s), lms);
+        static_assert(std::is_same<decltype(ztms), zoned_time<milliseconds, TimeZonePtr>>::value, "");
+    }
+
+    // local_time, choose
+    {
+        local_days ld(2017_y/feb/20);
+        zoned_time ztd(std::forward<Source>(s), ld, choose::earliest);
+        static_assert(std::is_same<decltype(ztd), zoned_time<seconds, TimeZonePtr>>::value, "");
+
+        local_time<seconds> ls(ld);
+        zoned_time zts(std::forward<Source>(s), ls, choose::earliest);
+        static_assert(std::is_same<decltype(zts), zoned_time<seconds, TimeZonePtr>>::value, "");
+
+        local_time<milliseconds> lms(ls);
+        zoned_time ztms(std::forward<Source>(s), lms, choose::earliest);
+        static_assert(std::is_same<decltype(ztms), zoned_time<milliseconds, TimeZonePtr>>::value, "");
+    }
+
+    // zoned_time
+    {
+        zoned_time<days> zd(sys_days(2017_y/feb/20));
+        zoned_time ztd(std::forward<Source>(s), zd);
+        static_assert(std::is_same<decltype(ztd), zoned_time<seconds, TimeZonePtr>>::value, "");
+
+        zoned_time<seconds> zs(zd);
+        zoned_time zts(std::forward<Source>(s), zs);
+        static_assert(std::is_same<decltype(zts), zoned_time<seconds, TimeZonePtr>>::value, "");
+
+        zoned_time<milliseconds> zms(zs);
+        zoned_time ztms(std::forward<Source>(s), zms);
+        static_assert(std::is_same<decltype(ztms), zoned_time<milliseconds, TimeZonePtr>>::value, "");
+    }
+
+    // zoned_time, choose
+    {
+        zoned_time<days> zd(sys_days(2017_y/feb/20));
+        zoned_time ztd(std::forward<Source>(s), zd, choose::earliest);
+        static_assert(std::is_same<decltype(ztd), zoned_time<seconds, TimeZonePtr>>::value, "");
+
+        zoned_time<seconds> zs(zd);
+        zoned_time zts(std::forward<Source>(s), zs, choose::earliest);
+        static_assert(std::is_same<decltype(zts), zoned_time<seconds, TimeZonePtr>>::value, "");
+
+        zoned_time<milliseconds> zms(zs);
+        zoned_time ztms(std::forward<Source>(s), zms, choose::earliest);
+        static_assert(std::is_same<decltype(ztms), zoned_time<milliseconds, TimeZonePtr>>::value, "");
+    }
+}
+
+struct MyString
+{
+  MyString(std::string s) : ms(std::move(s)) {}
+
+  operator std::string_view() const { return ms; }
+
+private:
+  std::string ms;
+};
+
+struct OnlyLValueString
+{
+  OnlyLValueString(std::string s) : ms(std::move(s)) {}
+
+  operator std::string_view() & { return ms; }
+
+private:
+  std::string ms;
+};
+
+#endif  // HAS_DEDUCTION_GUIDES
+
+template<typename T>
+T const& to_const(T& t) { return t; }
+
+
+int
+main()
+{
+    using namespace date;
+    using namespace std::chrono;
+
+#if HAS_DEDUCTION_GUIDES
+    //  no arguments
+    {
+        zoned_time zt{};
+        static_assert(std::is_same<decltype(zt), zoned_time<seconds>>::value, "");
+    } 
+
+    // zoned_time
+    {
+        zoned_time<days> zd(sys_days(2017_y/feb/20));
+        zoned_time ztd(zd);
+        static_assert(std::is_same<decltype(ztd), zoned_time<days>>::value, "");
+
+        zoned_time<seconds> zs(zd);
+        zoned_time zts(zs);
+        static_assert(std::is_same<decltype(zts), zoned_time<seconds>>::value, "");
+
+        zoned_time<milliseconds> zms(zs);
+        zoned_time ztms(zms);
+        static_assert(std::is_same<decltype(ztms), zoned_time<milliseconds>>::value, "");
+    }
+
+    // sys_time
+    {
+        sys_days sd(2017_y/feb/20);
+        zoned_time ztd(sd);
+        static_assert(std::is_same<decltype(ztd), zoned_time<seconds>>::value, "");
+
+        sys_time<seconds> ss(sd);
+        zoned_time zts(ss);
+        static_assert(std::is_same<decltype(zts), zoned_time<seconds>>::value, "");
+
+        sys_time<milliseconds> sms(ss);
+        zoned_time ztms(sms);
+        static_assert(std::is_same<decltype(ztms), zoned_time<milliseconds>>::value, "");
+    }
+
+    // time_zone const*
+    {
+       time_zone const* tz = current_zone();
+       testDeductionFrom<time_zone const*>(tz);
+       testDeductionFrom<time_zone const*>(to_const(tz));
+       testDeductionFrom<time_zone const*>(std::move(tz));
+    }
+
+    // char const*
+    {
+       char const* tz = "Europe/Warsaw";
+       testDeductionFrom<time_zone const*>(tz);
+       testDeductionFrom<time_zone const*>(to_const(tz));
+       testDeductionFrom<time_zone const*>(std::move(tz));
+    }
+
+    // std::string
+    {
+       std::string tz = "Europe/Warsaw";
+       testDeductionFrom<time_zone const*>(tz);
+       testDeductionFrom<time_zone const*>(to_const(tz));
+       testDeductionFrom<time_zone const*>(std::move(tz));
+    }
+
+    // std::string_view
+    {
+       std::string_view tz = "Europe/Warsaw";
+       testDeductionFrom<time_zone const*>(tz);
+       testDeductionFrom<time_zone const*>(to_const(tz));
+       testDeductionFrom<time_zone const*>(std::move(tz));
+    }
+
+    // MyString
+    {
+       MyString tz("Europe/Warsaw");
+       testDeductionFrom<time_zone const*>(tz);
+       testDeductionFrom<time_zone const*>(to_const(tz));
+       testDeductionFrom<time_zone const*>(std::move(tz));
+    }
+
+    // custom time zone
+    {
+       OffsetZone tz(minutes(45));
+       testDeductionFrom<OffsetZone>(tz);
+       testDeductionFrom<OffsetZone>(to_const(tz));
+       testDeductionFrom<OffsetZone>(std::move(tz));
+    }
+
+    // OnlyLValue
+    {
+       OnlyLValueString tz("Europe/Warsaw");
+       testDeductionFrom<time_zone const*>(tz);
+       //testDeductionFrom<time_zone const*>(to_const(tz));
+       //testDeductionFrom<time_zone const*>(std::move(tz));
+    }
+
+#endif  // HAS_DEDUCTION_GUIDES
+}
diff --git a/third_party/date-3.0.1/test_fail.sh b/third_party/date-3.0.1/test_fail.sh
new file mode 100644
index 00000000..65626476
--- /dev/null
+++ b/third_party/date-3.0.1/test_fail.sh
@@ -0,0 +1,10 @@
+#!/bin/bash
+
+echo $1
+eval $1
+
+if [ $? -eq 0 ]; then
+	exit 0;
+fi
+exit 1;
+