Credit GroupsCore.jl for origin of groups interface (#1641)

LICENSE.md

@@ -1,8 +1,13 @@
-As AbstractAlgebra links dynamically at runtime with various libraries included with Julia, all of whose licenses are compatible with GPL v3+, you may safely distribute AbstractAlgebra *as a whole* under the terms of that license. See for example the MPFR or GMP licenses in the Julia distribution, or refer to the GPL online here: 
+As AbstractAlgebra links dynamically at runtime with various libraries
+included with Julia, all of whose licenses are compatible with GPL v3+, you
+may safely distribute AbstractAlgebra *as a whole* under the terms of that
+license. See for example the MPFR or GMP licenses in the Julia distribution,
+or refer to the GPL online here:
 
-https://www.gnu.org/copyleft/gpl.txt
+<https://www.gnu.org/copyleft/gpl.txt>
 
-Individual parts of AbstractAlgebra may be distributed according to more permissive terms as laid out below:
+Individual parts of AbstractAlgebra may be distributed according to more
+permissive terms as laid out below:
 
 * The individual .jl files in the AbstractAlgebra.jl package are licensed under the Simplified "2-clause" BSD License:
 

src/Groups.jl

@@ -2,6 +2,17 @@
 #
 #   Groups.jl : AbstractAlgebra groups
 #
+#
+#  The code in this file is based on v0.4 of the GroupsCore.jl package, which
+#  is copyright (c) 2021 Marek Kaluba <[email protected]> and contributors,
+#  and licensed under the MIT license <https://spdx.org/licenses/MIT.html>.
+#
+#  The interfaces have since then diverged, with several breaking changes.
+#  Function and type names differ (e.g. `istrivial` vs. `is_trivial`), and
+#  also semantics (e.g. definition of equality for group elements in
+#  GroupsCore allows returning false for mathematically equal elements when it
+#  is "too hard" to prove equality; we don't).
+#
 ###############################################################################
 
 ###############################################################################

test/Groups-conformance-tests.jl

@@ -1,4 +1,20 @@
-# TODO: add acknowledgements for GroupsCore
+###############################################################################
+#
+#  Conformance tests for the group and group element interfaces.
+#
+#
+#  The code in this file is based on v0.4 of the GroupsCore.jl package, which
+#  is copyright (c) 2021 Marek Kaluba <[email protected]> and contributors,
+#  and licensed under the MIT license <https://spdx.org/licenses/MIT.html>.
+#
+#  The interfaces have since then diverged, with several breaking changes.
+#  Function and type names differ (e.g. `istrivial` vs. `is_trivial`), and
+#  also semantics (e.g. definition of equality for group elements in
+#  GroupsCore allows returning false for mathematically equal elements when it
+#  is "too hard" to prove equality; we don't).
+#
+###############################################################################
+
 
 function test_Group_interface(G::Group)
     @testset "Group interface" begin