diff --git a/include/frozen/algorithm.h b/include/frozen/algorithm.h
index a538f7c..7e02c5a 100644
--- a/include/frozen/algorithm.h
+++ b/include/frozen/algorithm.h
@@ -28,13 +28,11 @@
         #error \
             "frozen/algorithm.h requires C++23 or later. Compile with /std:c++latest or /std:c++23."
     #endif
-#elif __cplusplus < 202302L
+#elif __cplusplus < 202101L
     #error "frozen/algorithm.h requires C++23 or later. Compile with -std=c++23 or later."
 #endif
 
-#include "frozen/bits/basic_types.h"
-#include "frozen/bits/version.h"
-#include "frozen/string.h"
+#include "bits/basic_types.h"
 
 namespace frozen
 {
diff --git a/include/frozen/bits/algorithms.h b/include/frozen/bits/algorithms.h
index 310c31d..fc792f6 100644
--- a/include/frozen/bits/algorithms.h
+++ b/include/frozen/bits/algorithms.h
@@ -22,7 +22,7 @@
 
 #pragma once
 
-#include "frozen/bits/basic_types.h"
+#include "basic_types.h"
 
 #include <limits>
 #include <tuple>
diff --git a/include/frozen/bits/basic_types.h b/include/frozen/bits/basic_types.h
index 817908f..336229e 100644
--- a/include/frozen/bits/basic_types.h
+++ b/include/frozen/bits/basic_types.h
@@ -22,8 +22,8 @@
 
 #pragma once
 
-#include "frozen/bits/constexpr_assert.h"
-#include "frozen/bits/exceptions.h"
+#include "constexpr_assert.h"
+#include "exceptions.h"
 
 #include <array>
 #include <concepts>
diff --git a/include/frozen/bits/pmh.h b/include/frozen/bits/pmh.h
index 7591886..16f6d26 100644
--- a/include/frozen/bits/pmh.h
+++ b/include/frozen/bits/pmh.h
@@ -23,8 +23,8 @@
 // inspired from http://stevehanov.ca/blog/index.php?id=119
 #pragma once
 
-#include "frozen/bits/algorithms.h"
-#include "frozen/bits/basic_types.h"
+#include "algorithms.h"
+#include "basic_types.h"
 
 #include <cstddef>
 #include <cstdint>
diff --git a/include/frozen/bits/version.h b/include/frozen/bits/version.h
index a6278df..0d1e83f 100644
--- a/include/frozen/bits/version.h
+++ b/include/frozen/bits/version.h
@@ -27,7 +27,7 @@
     #if _MSVC_LANG < 202302L
         #error "frozen 2.0 requires C++23 or later. Compile with /std:c++latest or /std:c++23."
     #endif
-#elif __cplusplus < 202302L
+#elif __cplusplus < 202101L
     #error "frozen 2.0 requires C++23 or later. Compile with -std=c++23 or later."
 #endif
 
diff --git a/include/frozen/map.h b/include/frozen/map.h
index 733b51a..74dbcae 100644
--- a/include/frozen/map.h
+++ b/include/frozen/map.h
@@ -27,15 +27,14 @@
     #if _MSVC_LANG < 202302L
         #error "frozen/map.h requires C++23 or later. Compile with /std:c++latest or /std:c++23."
     #endif
-#elif __cplusplus < 202302L
+#elif __cplusplus < 202101L
     #error "frozen/map.h requires C++23 or later. Compile with -std=c++23 or later."
 #endif
 
-#include "frozen/bits/algorithms.h"
-#include "frozen/bits/basic_types.h"
-#include "frozen/bits/exceptions.h"
-#include "frozen/bits/mpl.h"
-#include "frozen/bits/version.h"
+#include "bits/algorithms.h"
+#include "bits/basic_types.h"
+#include "bits/exceptions.h"
+#include "bits/mpl.h"
 
 #include <functional>
 #include <iterator>
diff --git a/include/frozen/random.h b/include/frozen/random.h
index 1d41232..3c3681c 100644
--- a/include/frozen/random.h
+++ b/include/frozen/random.h
@@ -27,12 +27,11 @@
     #if _MSVC_LANG < 202302L
         #error "frozen/random.h requires C++23 or later. Compile with /std:c++latest or /std:c++23."
     #endif
-#elif __cplusplus < 202302L
+#elif __cplusplus < 202101L
     #error "frozen/random.h requires C++23 or later. Compile with -std=c++23 or later."
 #endif
 
-#include "frozen/bits/algorithms.h"
-#include "frozen/bits/version.h"
+#include "bits/algorithms.h"
 
 #include <concepts>
 #include <cstdint>
diff --git a/include/frozen/set.h b/include/frozen/set.h
index 2ee4195..dee8f0e 100644
--- a/include/frozen/set.h
+++ b/include/frozen/set.h
@@ -27,13 +27,12 @@
     #if _MSVC_LANG < 202302L
         #error "frozen/set.h requires C++23 or later. Compile with /std:c++latest or /std:c++23."
     #endif
-#elif __cplusplus < 202302L
+#elif __cplusplus < 202101L
     #error "frozen/set.h requires C++23 or later. Compile with -std=c++23 or later."
 #endif
 
-#include "frozen/bits/algorithms.h"
-#include "frozen/bits/basic_types.h"
-#include "frozen/bits/version.h"
+#include "bits/algorithms.h"
+#include "bits/basic_types.h"
 
 #include <functional>
 #include <iterator>
@@ -101,9 +100,10 @@ namespace frozen
         {
             const_iterator where = lower_bound(key);
             if ((where != end()) && !value_comp()(key, *where))
+            {
                 return where;
-            else
-                return end();
+            }
+            return end();
         }
 
         template <class KeyType>
@@ -118,9 +118,10 @@ namespace frozen
         {
             auto const lower = lower_bound(key);
             if (lower == end())
+            {
                 return { lower, lower };
-            else
-                return { lower, lower + 1 };
+            }
+            return { lower, lower + 1 };
         }
 
         template <class KeyType>
@@ -128,9 +129,10 @@ namespace frozen
         {
             auto const where = bits::lower_bound<N>(keys_.begin(), key, value_comp());
             if ((where != end()) && !value_comp()(key, *where))
+            {
                 return where;
-            else
-                return end();
+            }
+            return end();
         }
 
         template <class KeyType>
@@ -138,9 +140,10 @@ namespace frozen
         {
             auto const where = bits::lower_bound<N>(keys_.begin(), key, value_comp());
             if ((where != end()) && !value_comp()(key, *where))
+            {
                 return where + 1;
-            else
-                return end();
+            }
+            return end();
         }
 
         /* observers */
diff --git a/include/frozen/string.h b/include/frozen/string.h
index 71ad52d..ff2d85b 100644
--- a/include/frozen/string.h
+++ b/include/frozen/string.h
@@ -1,6 +1,14 @@
 #pragma once
 
-#include "frozen/bits/version.h"
+// Require C++23 or later
+#if defined(_MSVC_LANG)
+    #if _MSVC_LANG < 202302L
+        #error \
+            "frozen/unordered_map.h requires C++23 or later. Compile with /std:c++latest or /std:c++23."
+    #endif
+#elif __cplusplus < 202101L
+    #error "frozen/unordered_map.h requires C++23 or later. Compile with -std=c++23 or later."
+#endif
 
 #include <cstddef>
 #include <string_view>
diff --git a/include/frozen/unordered_map.h b/include/frozen/unordered_map.h
index cacea20..13e33e1 100644
--- a/include/frozen/unordered_map.h
+++ b/include/frozen/unordered_map.h
@@ -28,19 +28,17 @@
         #error \
             "frozen/unordered_map.h requires C++23 or later. Compile with /std:c++latest or /std:c++23."
     #endif
-#elif __cplusplus < 202302L
+#elif __cplusplus < 202101L
     #error "frozen/unordered_map.h requires C++23 or later. Compile with -std=c++23 or later."
 #endif
 
-#include "frozen/bits/basic_types.h"
-#include "frozen/bits/elsa.h"
-#include "frozen/bits/exceptions.h"
-#include "frozen/bits/pmh.h"
-#include "frozen/bits/version.h"
-#include "frozen/random.h"
+#include "bits/basic_types.h"
+#include "bits/elsa.h"
+#include "bits/exceptions.h"
+#include "bits/pmh.h"
+#include "random.h"
 
 #include <functional>
-#include <tuple>
 #include <utility>
 
 namespace frozen
diff --git a/include/frozen/unordered_set.h b/include/frozen/unordered_set.h
index 4d19112..c0e151a 100644
--- a/include/frozen/unordered_set.h
+++ b/include/frozen/unordered_set.h
@@ -28,15 +28,14 @@
         #error \
             "frozen/unordered_set.h requires C++23 or later. Compile with /std:c++latest or /std:c++23."
     #endif
-#elif __cplusplus < 202302L
+#elif __cplusplus < 202101L
     #error "frozen/unordered_set.h requires C++23 or later. Compile with -std=c++23 or later."
 #endif
 
-#include "frozen/bits/basic_types.h"
-#include "frozen/bits/elsa.h"
-#include "frozen/bits/pmh.h"
-#include "frozen/bits/version.h"
-#include "frozen/random.h"
+#include "bits/basic_types.h"
+#include "bits/elsa.h"
+#include "bits/pmh.h"
+#include "random.h"
 
 #include <functional>
 #include <utility>
@@ -50,7 +49,7 @@ namespace frozen
         struct Get
         {
             template <class T>
-            constexpr T const& operator()(T const& key) const
+            constexpr auto operator()(T const& key) const -> T const&
             {
                 return key;
             }
@@ -85,7 +84,6 @@ namespace frozen
         using const_iterator = typename container_type::const_iterator;
         using iterator = const_iterator;
 
-    public:
         /* constructors */
         unordered_set(unordered_set const&) = default;
         constexpr unordered_set(container_type keys, Hash const& hash, KeyEqual const& equal) :
@@ -111,72 +109,79 @@ namespace frozen
         }
 
         /* iterators */
-        [[nodiscard]] constexpr const_iterator begin() const { return keys_.begin(); }
-        [[nodiscard]] constexpr const_iterator end() const { return keys_.end(); }
-        [[nodiscard]] constexpr const_iterator cbegin() const { return keys_.begin(); }
-        [[nodiscard]] constexpr const_iterator cend() const { return keys_.end(); }
+        [[nodiscard]] constexpr auto begin() const -> const_iterator { return keys_.begin(); }
+        [[nodiscard]] constexpr auto end() const -> const_iterator { return keys_.end(); }
+        [[nodiscard]] constexpr auto cbegin() const -> const_iterator { return keys_.begin(); }
+        [[nodiscard]] constexpr auto cend() const -> const_iterator { return keys_.end(); }
 
         /* capacity */
-        [[nodiscard]] constexpr bool empty() const { return !N; }
-        [[nodiscard]] constexpr size_type size() const { return N; }
-        [[nodiscard]] constexpr size_type max_size() const { return N; }
+        [[nodiscard]] constexpr auto empty() const -> bool { return !N; }
+        [[nodiscard]] constexpr auto size() const -> size_type { return N; }
+        [[nodiscard]] constexpr auto max_size() const -> size_type { return N; }
 
         /* lookup */
         template <class KeyType>
-        [[nodiscard]] constexpr std::size_t count(KeyType const& key) const
+        [[nodiscard]] constexpr auto count(KeyType const& key) const -> std::size_t
         {
             return find(key, hash_function(), key_eq()) != end();
         }
 
         template <class KeyType, class Hasher, class Equal>
-        [[nodiscard]] constexpr const_iterator find(KeyType const& key, Hasher const& hash,
-                                                    Equal const& equal) const
+        [[nodiscard]] constexpr auto find(KeyType const& key, Hasher const& hash,
+                                          Equal const& equal) const -> const_iterator
         {
             auto const pos = tables_.lookup(key, hash);
-            auto it = keys_.begin() + pos;
-            if (it != keys_.end() && equal(*it, key))
-                return it;
-            else
-                return keys_.end();
+            auto iter = keys_.begin() + pos;
+            if (iter != keys_.end() && equal(*iter, key))
+            {
+                return iter;
+            }
+            return keys_.end();
         }
+
         template <class KeyType>
-        [[nodiscard]] constexpr const_iterator find(KeyType const& key) const
+        [[nodiscard]] constexpr auto find(KeyType const& key) const -> const_iterator
         {
             auto const pos = tables_.lookup(key, hash_function());
-            auto it = keys_.begin() + pos;
-            if (it != keys_.end() && key_eq()(*it, key))
-                return it;
-            else
-                return keys_.end();
+            auto iter = keys_.begin() + pos;
+            if (iter != keys_.end() && key_eq()(*iter, key))
+            {
+                return iter;
+            }
+            return keys_.end();
         }
 
         template <class KeyType>
-        [[nodiscard]] constexpr bool contains(KeyType const& key) const
+        [[nodiscard]] constexpr auto contains(KeyType const& key) const -> bool
         {
             return this->find(key) != keys_.end();
         }
 
         template <class KeyType>
-        [[nodiscard]] constexpr std::pair<const_iterator, const_iterator>
-            equal_range(KeyType const& key) const
+        [[nodiscard]] constexpr auto equal_range(KeyType const& key) const
+            -> std::pair<const_iterator, const_iterator>
         {
-            auto const it = find(key);
-            if (it != end())
-                return { it, it + 1 };
-            else
-                return { keys_.end(), keys_.end() };
+            auto const iter = find(key);
+            if (iter != end())
+            {
+                return { iter, iter + 1 };
+            }
+            return { keys_.end(), keys_.end() };
         }
 
         /* bucket interface */
-        [[nodiscard]] constexpr std::size_t bucket_count() const { return storage_size; }
-        [[nodiscard]] constexpr std::size_t max_bucket_count() const { return storage_size; }
+        [[nodiscard]] constexpr auto bucket_count() const -> std::size_t { return storage_size; }
+        [[nodiscard]] constexpr auto max_bucket_count() const -> std::size_t
+        {
+            return storage_size;
+        }
 
         /* observers*/
-        [[nodiscard]] constexpr const hasher& hash_function() const
+        [[nodiscard]] constexpr auto hash_function() const -> const hasher&
         {
             return tables_.hash_function();
         }
-        [[nodiscard]] constexpr const key_equal& key_eq() const
+        [[nodiscard]] constexpr auto key_eq() const -> const key_equal&
         {
             return static_cast<KeyEqual const&>(*this);
         }