diff --git a/README.md b/README.md
index 5c2e7dc26..dcf19d464 100644
--- a/README.md
+++ b/README.md
@@ -91,7 +91,7 @@ Procedures for each standard are provided by the following R7RS-style libraries:
 cmake -B build -DCMAKE_BUILD_TYPE=Release
 cd build
 make package
-sudo apt install build/meevax_0.5.62_amd64.deb
+sudo apt install build/meevax_0.5.63_amd64.deb
 ```
 
 or
@@ -123,9 +123,9 @@ sudo rm -rf /usr/local/share/meevax
 
 | Target Name | Description
 |-------------|-------------
-| `all`       | Build shared-library `libmeevax.0.5.62.so` and executable `meevax`
+| `all`       | Build shared-library `libmeevax.0.5.63.so` and executable `meevax`
 | `test`      | Test executable `meevax`
-| `package`   | Generate debian package `meevax_0.5.62_amd64.deb`
+| `package`   | Generate debian package `meevax_0.5.63_amd64.deb`
 | `install`   | Copy files into `/usr/local` directly
 
 ## Usage
diff --git a/VERSION b/VERSION
index 1efaf43fe..08c80f334 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-0.5.62
+0.5.63
diff --git a/include/meevax/memory/unsigned_integer_set.hpp b/include/meevax/memory/unsigned_integer_set.hpp
deleted file mode 100644
index 79c516e09..000000000
--- a/include/meevax/memory/unsigned_integer_set.hpp
+++ /dev/null
@@ -1,200 +0,0 @@
-/*
-   Copyright 2018-2023 Tatsuya Yamasaki.
-
-   Licensed under the Apache License, Version 2.0 (the "License");
-   you may not use this file except in compliance with the License.
-   You may obtain a copy of the License at
-
-       http://www.apache.org/licenses/LICENSE-2.0
-
-   Unless required by applicable law or agreed to in writing, software
-   distributed under the License is distributed on an "AS IS" BASIS,
-   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-   See the License for the specific language governing permissions and
-   limitations under the License.
-*/
-
-#ifndef INCLUDED_MEEVAX_MEMORY_UNSIGNED_INTEGER_SET_HPP
-#define INCLUDED_MEEVAX_MEMORY_UNSIGNED_INTEGER_SET_HPP
-
-#include <algorithm>
-#include <cstdint>
-#include <iterator>
-#include <limits>
-#include <vector>
-
-namespace meevax
-{
-inline namespace memory
-{
-  template <typename N>
-  constexpr auto log2(N n) -> std::size_t
-  {
-    return n <= 2 ? 1 : log2(n / 2) + 1;
-  }
-
-  class unsigned_integer_set
-  {
-    std::size_t size;
-
-    std::vector<std::uint64_t> data;
-
-    static constexpr auto digits = std::numeric_limits<std::uint64_t>::digits;
-
-    constexpr auto index_of(std::size_t value)
-    {
-      return value / digits;
-    };
-
-    constexpr auto mark_of(std::size_t value)
-    {
-      return static_cast<std::uint64_t>(1) << (value - digits * index_of(value));
-    };
-
-  public:
-    struct iterator
-    {
-      using iterator_category = std::forward_iterator_tag;
-
-      using value_type = std::uint64_t;
-
-      using difference_type = std::ptrdiff_t;
-
-      std::uint64_t const* data;
-
-      std::size_t size;
-
-      std::size_t index;
-
-      std::size_t bit;
-
-      explicit iterator(std::vector<std::uint64_t> const& bitset)
-        : data { bitset.data() }
-        , size { bitset.size() }
-        , index { 0 }
-        , bit { 0 }
-      {
-        if (not valid())
-        {
-          operator ++();
-        }
-      }
-
-      explicit iterator()
-        : data { nullptr }
-        , size { 0 }
-        , index { std::numeric_limits<std::size_t>::max() }
-        , bit { 0 }
-      {}
-
-      auto valid() const -> bool
-      {
-        return (data[index] >> bit) & 1;
-      }
-
-      auto operator *() const
-      {
-        return index * digits + bit;
-      }
-
-      auto operator ++() -> iterator &
-      {
-        do
-        {
-          if (digits <= ++bit)
-          {
-            bit = 0;
-
-            if (size <= ++index)
-            {
-              index = std::numeric_limits<std::size_t>::max();
-              return *this;
-            }
-          }
-        }
-        while (not valid());
-
-        return *this;
-      }
-
-      auto operator ++(int) -> auto
-      {
-        auto copy = *this;
-        operator ++();
-        return copy;
-      }
-
-      auto operator ==(iterator const& rhs)
-      {
-        return index == rhs.index and bit == rhs.bit;
-      }
-
-      auto operator !=(iterator const& rhs)
-      {
-        return not operator ==(rhs);
-      }
-    };
-
-    explicit unsigned_integer_set()
-      : size { 0 }
-      , data {}
-    {}
-
-    auto resize(std::size_t given_size)
-    {
-      size = given_size;
-      data.resize(size / digits + 1);
-    }
-
-    auto insert(std::uint64_t value)
-    {
-      if (data.size() < index_of(value))
-      {
-        resize(value);
-      }
-
-      data[index_of(value)] |= mark_of(value);
-    }
-
-    auto erase(std::uint64_t value)
-    {
-      data[index_of(value)] &= ~mark_of(value);
-    }
-
-    auto erase(iterator iter)
-    {
-      erase(*iter);
-      return ++iter;
-    }
-
-    auto clear()
-    {
-      std::fill(std::begin(data), std::end(data), 0);
-    }
-
-    auto begin() const
-    {
-      return iterator(data);
-    }
-
-    auto end() const
-    {
-      return iterator();
-    }
-
-    template <typename... Ts>
-    auto lower_bound(Ts&&... xs)
-    {
-      return std::lower_bound(begin(), end(), std::forward<decltype(xs)>(xs)...);
-    }
-
-    template <typename... Ts>
-    auto upper_bound(Ts&&... xs)
-    {
-      return std::upper_bound(begin(), end(), std::forward<decltype(xs)>(xs)...);
-    }
-  };
-} // namespace memory
-} // namespace meevax
-
-#endif // INCLUDED_MEEVAX_MEMORY_UNSIGNED_INTEGER_SET_HPP