diff --git a/ctl/add_lvalue_reference.h b/ctl/add_lvalue_reference.h
new file mode 100644
index 000000000..9d0c48b1d
--- /dev/null
+++ b/ctl/add_lvalue_reference.h
@@ -0,0 +1,55 @@
+// -*-mode:c++;indent-tabs-mode:nil;c-basic-offset:4;tab-width:8;coding:utf-8-*-
+// vi: set et ft=cpp ts=4 sts=4 sw=4 fenc=utf-8 :vi
+#ifndef CTL_ADD_LVALUE_REFERENCE_H_
+#define CTL_ADD_LVALUE_REFERENCE_H_
+
+namespace ctl {
+
+template<typename T>
+struct add_lvalue_reference
+{
+    typedef T& type;
+};
+
+template<typename T>
+struct add_lvalue_reference<T&>
+{
+    typedef T& type;
+};
+
+template<typename T>
+struct add_lvalue_reference<T&&>
+{
+    typedef T& type;
+};
+
+template<>
+struct add_lvalue_reference<void>
+{
+    typedef void type;
+};
+
+template<>
+struct add_lvalue_reference<const void>
+{
+    typedef const void type;
+};
+
+template<>
+struct add_lvalue_reference<volatile void>
+{
+    typedef volatile void type;
+};
+
+template<>
+struct add_lvalue_reference<const volatile void>
+{
+    typedef const volatile void type;
+};
+
+template<typename T>
+using add_lvalue_reference_t = typename add_lvalue_reference<T>::type;
+
+} // namespace ctl
+
+#endif // CTL_ADD_LVALUE_REFERENCE_H_
diff --git a/ctl/add_pointer.h b/ctl/add_pointer.h
new file mode 100644
index 000000000..005a4a09a
--- /dev/null
+++ b/ctl/add_pointer.h
@@ -0,0 +1,43 @@
+// -*-mode:c++;indent-tabs-mode:nil;c-basic-offset:4;tab-width:8;coding:utf-8-*-
+// vi: set et ft=cpp ts=4 sts=4 sw=4 fenc=utf-8 :vi
+#ifndef CTL_ADD_POINTER_H_
+#define CTL_ADD_POINTER_H_
+#include "remove_reference.h"
+
+namespace ctl {
+
+// Primary template
+template<typename T>
+struct add_pointer
+{
+    typedef typename remove_reference<T>::type* type;
+};
+
+// Specialization for functions
+template<typename R, typename... Args>
+struct add_pointer<R(Args...)>
+{
+    typedef R (*type)(Args...);
+};
+
+// Specialization for function references
+template<typename R, typename... Args>
+struct add_pointer<R (&)(Args...)>
+{
+    typedef R (*type)(Args...);
+};
+
+// Specialization for rvalue references to functions
+template<typename R, typename... Args>
+struct add_pointer<R (&&)(Args...)>
+{
+    typedef R (*type)(Args...);
+};
+
+// Helper alias template (C++14 and later)
+template<typename T>
+using add_pointer_t = typename add_pointer<T>::type;
+
+} // namespace ctl
+
+#endif // CTL_ADD_POINTER_H_
diff --git a/ctl/all_of.h b/ctl/all_of.h
index 8934668a2..0c258bc4a 100644
--- a/ctl/all_of.h
+++ b/ctl/all_of.h
@@ -9,11 +9,9 @@ template<class InputIt, class UnaryPredicate>
 constexpr bool
 all_of(InputIt first, InputIt last, UnaryPredicate p)
 {
-    for (; first != last; ++first) {
-        if (!p(*first)) {
+    for (; first != last; ++first)
+        if (!p(*first))
             return false;
-        }
-    }
     return true;
 }
 
diff --git a/ctl/allocator.h b/ctl/allocator.h
index b084f10e9..3a593d363 100644
--- a/ctl/allocator.h
+++ b/ctl/allocator.h
@@ -3,8 +3,8 @@
 #ifndef CTL_ALLOCATOR_H_
 #define CTL_ALLOCATOR_H_
 #include "bad_alloc.h"
+#include "integral_constant.h"
 #include "new.h"
-#include "type_traits.h"
 #include "utility.h"
 
 namespace ctl {
diff --git a/ctl/allocator_traits.h b/ctl/allocator_traits.h
index 42d43d84d..ebdf03424 100644
--- a/ctl/allocator_traits.h
+++ b/ctl/allocator_traits.h
@@ -1,6 +1,8 @@
+// -*-mode:c++;indent-tabs-mode:nil;c-basic-offset:4;tab-width:8;coding:utf-8-*-
+// vi: set et ft=cpp ts=4 sts=4 sw=4 fenc=utf-8 :vi
 #ifndef CTL_ALLOCATOR_TRAITS_H_
 #define CTL_ALLOCATOR_TRAITS_H_
-#include "type_traits.h"
+#include "integral_constant.h"
 
 namespace ctl {
 
diff --git a/ctl/any_of.h b/ctl/any_of.h
index 7eec80605..09c9bcfbd 100644
--- a/ctl/any_of.h
+++ b/ctl/any_of.h
@@ -9,11 +9,9 @@ template<class InputIt, class UnaryPredicate>
 constexpr bool
 any_of(InputIt first, InputIt last, UnaryPredicate p)
 {
-    for (; first != last; ++first) {
-        if (p(*first)) {
+    for (; first != last; ++first)
+        if (p(*first))
             return true;
-        }
-    }
     return false;
 }
 
diff --git a/ctl/array.h b/ctl/array.h
index fda2ddd04..a2b5925b5 100644
--- a/ctl/array.h
+++ b/ctl/array.h
@@ -3,6 +3,7 @@
 #ifndef CTL_ARRAY_H_
 #define CTL_ARRAY_H_
 #include "initializer_list.h"
+#include "out_of_range.h"
 #include "reverse_iterator.h"
 
 namespace ctl {
@@ -25,25 +26,25 @@ struct array
     T elems[N];
 
     constexpr array() = default;
+
     constexpr array(std::initializer_list<T> init)
     {
         auto it = init.begin();
-        for (size_t i = 0; i < N && it != init.end(); ++i, ++it) {
+        for (size_t i = 0; i < N && it != init.end(); ++i, ++it)
             elems[i] = *it;
-        }
     }
 
     constexpr reference at(size_type pos)
     {
         if (pos >= N)
-            __builtin_trap();
+            throw ctl::out_of_range("out of range");
         return elems[pos];
     }
 
     constexpr const_reference at(size_type pos) const
     {
         if (pos >= N)
-            __builtin_trap();
+            throw ctl::out_of_range("out of range");
         return elems[pos];
     }
 
diff --git a/ctl/conditional.h b/ctl/conditional.h
new file mode 100644
index 000000000..976143a1d
--- /dev/null
+++ b/ctl/conditional.h
@@ -0,0 +1,22 @@
+// -*-mode:c++;indent-tabs-mode:nil;c-basic-offset:4;tab-width:8;coding:utf-8-*-
+// vi: set et ft=cpp ts=4 sts=4 sw=4 fenc=utf-8 :vi
+#ifndef CTL_CONDITIONAL_H_
+#define CTL_CONDITIONAL_H_
+
+namespace ctl {
+
+template<bool B, class T, class F>
+struct conditional
+{
+    typedef T type;
+};
+
+template<class T, class F>
+struct conditional<false, T, F>
+{
+    typedef F type;
+};
+
+} // namespace ctl
+
+#endif // CTL_CONDITIONAL_H_
diff --git a/ctl/decay.h b/ctl/decay.h
new file mode 100644
index 000000000..6c4fe6f2a
--- /dev/null
+++ b/ctl/decay.h
@@ -0,0 +1,35 @@
+// -*-mode:c++;indent-tabs-mode:nil;c-basic-offset:4;tab-width:8;coding:utf-8-*-
+// vi: set et ft=cpp ts=4 sts=4 sw=4 fenc=utf-8 :vi
+#ifndef CTL_DECAY_H_
+#define CTL_DECAY_H_
+#include "add_pointer.h"
+#include "conditional.h"
+#include "is_array.h"
+#include "is_function.h"
+#include "remove_cv.h"
+#include "remove_extent.h"
+#include "remove_reference.h"
+
+namespace ctl {
+
+template<typename T>
+struct decay
+{
+  private:
+    typedef typename remove_reference<T>::type U;
+
+  public:
+    typedef typename conditional<
+      is_array<U>::value,
+      typename remove_extent<U>::type*,
+      typename conditional<is_function<U>::value,
+                           typename add_pointer<U>::type,
+                           typename remove_cv<U>::type>::type>::type type;
+};
+
+template<typename T>
+using decay_t = typename decay<T>::type;
+
+} // namespace ctl
+
+#endif // CTL_DECAY_H_
diff --git a/ctl/default_delete.h b/ctl/default_delete.h
new file mode 100644
index 000000000..4a3458369
--- /dev/null
+++ b/ctl/default_delete.h
@@ -0,0 +1,44 @@
+// -*-mode:c++;indent-tabs-mode:nil;c-basic-offset:4;tab-width:8;coding:utf-8-*-
+// vi: set et ft=cpp ts=4 sts=4 sw=4 fenc=utf-8 :vi
+#ifndef CTL_DEFAULT_DELETE_H_
+#define CTL_DEFAULT_DELETE_H_
+#include "enable_if.h"
+#include "is_convertible.h"
+
+namespace ctl {
+
+template<typename T>
+struct default_delete
+{
+    constexpr default_delete() noexcept = default;
+    template<typename U,
+             typename = typename ctl::enable_if<
+               ctl::is_convertible<U*, T*>::value>::type>
+    constexpr default_delete(const default_delete<U>&) noexcept
+    {
+    }
+    constexpr void operator()(T* const p) const noexcept
+    {
+        delete p;
+    }
+};
+
+template<typename T>
+struct default_delete<T[]>
+{
+    constexpr default_delete() noexcept = default;
+    template<typename U,
+             typename = typename ctl::enable_if<
+               ctl::is_convertible<U (*)[], T (*)[]>::value>::type>
+    constexpr default_delete(const default_delete<U[]>&) noexcept
+    {
+    }
+    constexpr void operator()(T* const p) const noexcept
+    {
+        delete[] p;
+    }
+};
+
+} // namespace ctl
+
+#endif // CTL_DEFAULT_DELETE_H_
diff --git a/ctl/enable_if.h b/ctl/enable_if.h
index 70cb862a3..9c61957a4 100644
--- a/ctl/enable_if.h
+++ b/ctl/enable_if.h
@@ -1,3 +1,5 @@
+// -*-mode:c++;indent-tabs-mode:nil;c-basic-offset:4;tab-width:8;coding:utf-8-*-
+// vi: set et ft=cpp ts=4 sts=4 sw=4 fenc=utf-8 :vi
 #ifndef CTL_ENABLE_IF_H_
 #define CTL_ENABLE_IF_H_
 
diff --git a/ctl/integral_constant.h b/ctl/integral_constant.h
new file mode 100644
index 000000000..df5a0a688
--- /dev/null
+++ b/ctl/integral_constant.h
@@ -0,0 +1,29 @@
+// -*-mode:c++;indent-tabs-mode:nil;c-basic-offset:4;tab-width:8;coding:utf-8-*-
+// vi: set et ft=cpp ts=4 sts=4 sw=4 fenc=utf-8 :vi
+#ifndef CTL_INTEGRAL_CONSTANT_H_
+#define CTL_INTEGRAL_CONSTANT_H_
+
+namespace ctl {
+
+template<class T, T v>
+struct integral_constant
+{
+    static constexpr T value = v;
+    typedef T value_type;
+    typedef integral_constant type;
+    constexpr operator value_type() const noexcept
+    {
+        return value;
+    }
+    constexpr value_type operator()() const noexcept
+    {
+        return value;
+    }
+};
+
+typedef integral_constant<bool, true> true_type;
+typedef integral_constant<bool, false> false_type;
+
+} // namespace ctl
+
+#endif // CTL_INTEGRAL_CONSTANT_H_
diff --git a/ctl/is_array.h b/ctl/is_array.h
new file mode 100644
index 000000000..946d152ea
--- /dev/null
+++ b/ctl/is_array.h
@@ -0,0 +1,26 @@
+// -*-mode:c++;indent-tabs-mode:nil;c-basic-offset:4;tab-width:8;coding:utf-8-*-
+// vi: set et ft=cpp ts=4 sts=4 sw=4 fenc=utf-8 :vi
+#ifndef CTL_IS_ARRAY_H_
+#define CTL_IS_ARRAY_H_
+#include "integral_constant.h"
+
+namespace ctl {
+
+template<typename T>
+struct is_array : false_type
+{};
+
+template<typename T, size_t N>
+struct is_array<T[N]> : true_type
+{};
+
+template<typename T>
+struct is_array<T[]> : true_type
+{};
+
+template<typename T>
+inline constexpr bool is_array_v = is_array<T>::value;
+
+} // namespace ctl
+
+#endif // CTL_IS_ARRAY_H_
diff --git a/ctl/is_convertible.h b/ctl/is_convertible.h
new file mode 100644
index 000000000..9b81747e8
--- /dev/null
+++ b/ctl/is_convertible.h
@@ -0,0 +1,54 @@
+// -*-mode:c++;indent-tabs-mode:nil;c-basic-offset:4;tab-width:8;coding:utf-8-*-
+// vi: set et ft=cpp ts=4 sts=4 sw=4 fenc=utf-8 :vi
+#ifndef CTL_IS_CONVERTIBLE_H_
+#define CTL_IS_CONVERTIBLE_H_
+
+#include "ctl/integral_constant.h"
+#include "ctl/void_t.h"
+
+namespace ctl {
+
+// Declaration of declval
+template<typename T>
+T&&
+declval() noexcept;
+
+namespace detail {
+
+template<typename From, typename To, typename = void>
+struct is_convertible_impl : false_type
+{};
+
+template<typename From, typename To>
+struct is_convertible_impl<From,
+                           To,
+                           void_t<decltype(static_cast<To>(declval<From>()))>>
+  : true_type
+{};
+
+// Handle void types separately
+template<>
+struct is_convertible_impl<void, void> : true_type
+{};
+
+template<typename To>
+struct is_convertible_impl<void, To> : false_type
+{};
+
+template<typename From>
+struct is_convertible_impl<From, void> : false_type
+{};
+
+} // namespace detail
+
+template<typename From, typename To>
+struct is_convertible : detail::is_convertible_impl<From, To>
+{};
+
+// Helper variable template (C++17 and later)
+template<typename From, typename To>
+inline constexpr bool is_convertible_v = is_convertible<From, To>::value;
+
+} // namespace ctl
+
+#endif // CTL_IS_CONVERTIBLE_H_
diff --git a/ctl/is_function.h b/ctl/is_function.h
new file mode 100644
index 000000000..667a1e8eb
--- /dev/null
+++ b/ctl/is_function.h
@@ -0,0 +1,120 @@
+// -*-mode:c++;indent-tabs-mode:nil;c-basic-offset:4;tab-width:8;coding:utf-8-*-
+// vi: set et ft=cpp ts=4 sts=4 sw=4 fenc=utf-8 :vi
+#ifndef CTL_IS_FUNCTION_H_
+#define CTL_IS_FUNCTION_H_
+#include "integral_constant.h"
+
+namespace ctl {
+
+// Primary template
+template<class>
+struct is_function : false_type
+{};
+
+// Specializations for various function types
+
+// Regular functions
+template<class Ret, class... Args>
+struct is_function<Ret(Args...)> : true_type
+{};
+
+// Functions with cv-qualifiers
+template<class Ret, class... Args>
+struct is_function<Ret(Args...) const> : true_type
+{};
+
+template<class Ret, class... Args>
+struct is_function<Ret(Args...) volatile> : true_type
+{};
+
+template<class Ret, class... Args>
+struct is_function<Ret(Args...) const volatile> : true_type
+{};
+
+// Functions with ref-qualifiers
+template<class Ret, class... Args>
+struct is_function<Ret(Args...)&> : true_type
+{};
+
+template<class Ret, class... Args>
+struct is_function<Ret(Args...) const&> : true_type
+{};
+
+template<class Ret, class... Args>
+struct is_function<Ret(Args...) volatile&> : true_type
+{};
+
+template<class Ret, class... Args>
+struct is_function<Ret(Args...) const volatile&> : true_type
+{};
+
+template<class Ret, class... Args>
+struct is_function<Ret(Args...) &&> : true_type
+{};
+
+template<class Ret, class... Args>
+struct is_function<Ret(Args...) const&&> : true_type
+{};
+
+template<class Ret, class... Args>
+struct is_function<Ret(Args...) volatile&&> : true_type
+{};
+
+template<class Ret, class... Args>
+struct is_function<Ret(Args...) const volatile&&> : true_type
+{};
+
+// Variadic functions
+template<class Ret, class... Args>
+struct is_function<Ret(Args..., ...)> : true_type
+{};
+
+// Variadic functions with cv-qualifiers
+template<class Ret, class... Args>
+struct is_function<Ret(Args..., ...) const> : true_type
+{};
+
+template<class Ret, class... Args>
+struct is_function<Ret(Args..., ...) volatile> : true_type
+{};
+
+template<class Ret, class... Args>
+struct is_function<Ret(Args..., ...) const volatile> : true_type
+{};
+
+// Variadic functions with ref-qualifiers
+template<class Ret, class... Args>
+struct is_function<Ret(Args..., ...)&> : true_type
+{};
+
+template<class Ret, class... Args>
+struct is_function<Ret(Args..., ...) const&> : true_type
+{};
+
+template<class Ret, class... Args>
+struct is_function<Ret(Args..., ...) volatile&> : true_type
+{};
+
+template<class Ret, class... Args>
+struct is_function<Ret(Args..., ...) const volatile&> : true_type
+{};
+
+template<class Ret, class... Args>
+struct is_function<Ret(Args..., ...) &&> : true_type
+{};
+
+template<class Ret, class... Args>
+struct is_function<Ret(Args..., ...) const&&> : true_type
+{};
+
+template<class Ret, class... Args>
+struct is_function<Ret(Args..., ...) volatile&&> : true_type
+{};
+
+template<class Ret, class... Args>
+struct is_function<Ret(Args..., ...) const volatile&&> : true_type
+{};
+
+} // namespace ctl
+
+#endif // CTL_IS_FUNCTION_H_
diff --git a/ctl/type_traits.h b/ctl/is_integral.h
similarity index 55%
rename from ctl/type_traits.h
rename to ctl/is_integral.h
index c9dea8584..384985a38 100644
--- a/ctl/type_traits.h
+++ b/ctl/is_integral.h
@@ -1,29 +1,11 @@
 // -*-mode:c++;indent-tabs-mode:nil;c-basic-offset:4;tab-width:8;coding:utf-8-*-
 // vi: set et ft=cpp ts=4 sts=4 sw=4 fenc=utf-8 :vi
-#ifndef CTL_TYPE_TRAITS_H_
-#define CTL_TYPE_TRAITS_H_
+#ifndef CTL_IS_INTEGRAL_H_
+#define CTL_IS_INTEGRAL_H_
+#include "integral_constant.h"
 
 namespace ctl {
 
-template<class T, T v>
-struct integral_constant
-{
-    static constexpr T value = v;
-    using value_type = T;
-    using type = integral_constant;
-    constexpr operator value_type() const noexcept
-    {
-        return value;
-    }
-    constexpr value_type operator()() const noexcept
-    {
-        return value;
-    }
-};
-
-using true_type = integral_constant<bool, true>;
-using false_type = integral_constant<bool, false>;
-
 template<typename T>
 struct is_integral : false_type
 {};
@@ -91,33 +73,6 @@ struct is_integral<wchar_t> : true_type
 template<typename T>
 inline constexpr bool is_integral_v = is_integral<T>::value;
 
-template<typename T>
-struct is_signed
-{
-    static constexpr bool value = T(0) > T(-1);
-};
-
-template<typename T>
-struct is_unsigned
-{
-    static constexpr bool value = T(0) < T(-1);
-};
-
-template<typename T, typename U>
-struct is_same
-{
-    static constexpr bool value = false;
-};
-
-template<typename T>
-struct is_same<T, T>
-{
-    static constexpr bool value = true;
-};
-
-template<class T, class U>
-inline constexpr bool is_same_v = is_same<T, U>::value;
-
 } // namespace ctl
 
-#endif // CTL_TYPE_TRAITS_H_
+#endif // CTL_IS_INTEGRAL_H_
diff --git a/ctl/is_reference.h b/ctl/is_reference.h
new file mode 100644
index 000000000..66ae107b6
--- /dev/null
+++ b/ctl/is_reference.h
@@ -0,0 +1,35 @@
+// -*-mode:c++;indent-tabs-mode:nil;c-basic-offset:4;tab-width:8;coding:utf-8-*-
+// vi: set et ft=cpp ts=4 sts=4 sw=4 fenc=utf-8 :vi
+#ifndef CTL_IS_REFERENCE_H_
+#define CTL_IS_REFERENCE_H_
+
+namespace ctl {
+
+// Primary template
+template<class T>
+struct is_reference
+{
+    static constexpr bool value = false;
+};
+
+// Specialization for lvalue reference
+template<class T>
+struct is_reference<T&>
+{
+    static constexpr bool value = true;
+};
+
+// Specialization for rvalue reference
+template<class T>
+struct is_reference<T&&>
+{
+    static constexpr bool value = true;
+};
+
+// Helper variable template (C++14 and later)
+template<class T>
+inline constexpr bool is_reference_v = is_reference<T>::value;
+
+} // namespace ctl
+
+#endif // CTL_IS_REFERENCE_H_
diff --git a/ctl/is_same.h b/ctl/is_same.h
new file mode 100644
index 000000000..44c09761b
--- /dev/null
+++ b/ctl/is_same.h
@@ -0,0 +1,25 @@
+// -*-mode:c++;indent-tabs-mode:nil;c-basic-offset:4;tab-width:8;coding:utf-8-*-
+// vi: set et ft=cpp ts=4 sts=4 sw=4 fenc=utf-8 :vi
+#ifndef CTL_IS_SAME_H_
+#define CTL_IS_SAME_H_
+
+namespace ctl {
+
+template<typename T, typename U>
+struct is_same
+{
+    static constexpr bool value = false;
+};
+
+template<typename T>
+struct is_same<T, T>
+{
+    static constexpr bool value = true;
+};
+
+template<class T, class U>
+inline constexpr bool is_same_v = is_same<T, U>::value;
+
+} // namespace ctl
+
+#endif // CTL_IS_SAME_H_
diff --git a/ctl/is_signed.h b/ctl/is_signed.h
new file mode 100644
index 000000000..2c911ee4c
--- /dev/null
+++ b/ctl/is_signed.h
@@ -0,0 +1,16 @@
+// -*-mode:c++;indent-tabs-mode:nil;c-basic-offset:4;tab-width:8;coding:utf-8-*-
+// vi: set et ft=cpp ts=4 sts=4 sw=4 fenc=utf-8 :vi
+#ifndef CTL_IS_SIGNED_H_
+#define CTL_IS_SIGNED_H_
+
+namespace ctl {
+
+template<typename T>
+struct is_signed
+{
+    static constexpr bool value = T(0) > T(-1);
+};
+
+} // namespace ctl
+
+#endif // CTL_IS_SIGNED_H_
diff --git a/ctl/is_sorted.h b/ctl/is_sorted.h
new file mode 100644
index 000000000..551cce9da
--- /dev/null
+++ b/ctl/is_sorted.h
@@ -0,0 +1,25 @@
+// -*-mode:c++;indent-tabs-mode:nil;c-basic-offset:4;tab-width:8;coding:utf-8-*-
+// vi: set et ft=cpp ts=4 sts=4 sw=4 fenc=utf-8 :vi
+#ifndef CTL_IS_SORTED_H_
+#define CTL_IS_SORTED_H_
+
+namespace ctl {
+
+template<typename It, typename Compare>
+bool
+is_sorted(It first, It last, Compare comp)
+{
+    if (first == last)
+        return true;
+    It next = first;
+    while (++next != last) {
+        if (comp(*next, *first))
+            return false;
+        first = next;
+    }
+    return true;
+}
+
+} // namespace ctl
+
+#endif // CTL_IS_SORTED_H_
diff --git a/ctl/is_unsigned.h b/ctl/is_unsigned.h
new file mode 100644
index 000000000..02f276a7c
--- /dev/null
+++ b/ctl/is_unsigned.h
@@ -0,0 +1,16 @@
+// -*-mode:c++;indent-tabs-mode:nil;c-basic-offset:4;tab-width:8;coding:utf-8-*-
+// vi: set et ft=cpp ts=4 sts=4 sw=4 fenc=utf-8 :vi
+#ifndef CTL_IS_UNSIGNED_H_
+#define CTL_IS_UNSIGNED_H_
+
+namespace ctl {
+
+template<typename T>
+struct is_unsigned
+{
+    static constexpr bool value = T(0) < T(-1);
+};
+
+} // namespace ctl
+
+#endif // CTL_IS_UNSIGNED_H_
diff --git a/ctl/move_iterator.h b/ctl/move_iterator.h
index 8ce1ed05b..2527eca3b 100644
--- a/ctl/move_iterator.h
+++ b/ctl/move_iterator.h
@@ -1,7 +1,6 @@
 #ifndef CTL_MOVE_ITERATOR_H_
 #define CTL_MOVE_ITERATOR_H_
 #include "iterator_traits.h"
-#include "type_traits.h"
 
 namespace ctl {
 
diff --git a/ctl/mutex.h b/ctl/mutex.h
new file mode 100644
index 000000000..28a21e2e7
--- /dev/null
+++ b/ctl/mutex.h
@@ -0,0 +1,47 @@
+// -*-mode:c++;indent-tabs-mode:nil;c-basic-offset:4;tab-width:8;coding:utf-8-*-
+// vi: set et ft=cpp ts=4 sts=4 sw=4 fenc=utf-8 :vi
+#ifndef CTL_MUTEX_H_
+#define CTL_MUTEX_H_
+#include "libc/thread/thread.h"
+
+namespace ctl {
+
+class mutex
+{
+  public:
+    mutex()
+    {
+        pthread_mutex_init(&m_, nullptr);
+    }
+
+    ~mutex()
+    {
+        pthread_mutex_destroy(&m_);
+    }
+
+    void lock()
+    {
+        pthread_mutex_lock(&m_);
+    }
+
+    bool try_lock()
+    {
+        return pthread_mutex_trylock(&m_) == 0;
+    }
+
+    void unlock()
+    {
+        pthread_mutex_unlock(&m_);
+    }
+
+    // Delete copy constructor and assignment operator
+    mutex(const mutex&) = delete;
+    mutex& operator=(const mutex&) = delete;
+
+  private:
+    pthread_mutex_t m_;
+};
+
+} // namespace ctl
+
+#endif // CTL_MUTEX_H_
diff --git a/ctl/numeric_limits.h b/ctl/numeric_limits.h
index 5693a62e2..41aea3ae2 100644
--- a/ctl/numeric_limits.h
+++ b/ctl/numeric_limits.h
@@ -2,7 +2,8 @@
 // vi: set et ft=cpp ts=4 sts=4 sw=4 fenc=utf-8 :vi
 #ifndef CTL_NUMERIC_LIMITS_H_
 #define CTL_NUMERIC_LIMITS_H_
-#include "type_traits.h"
+#include "is_integral.h"
+#include "is_unsigned.h"
 
 namespace ctl {
 
diff --git a/ctl/partition.h b/ctl/partition.h
new file mode 100644
index 000000000..a1db21fb2
--- /dev/null
+++ b/ctl/partition.h
@@ -0,0 +1,29 @@
+// -*-mode:c++;indent-tabs-mode:nil;c-basic-offset:4;tab-width:8;coding:utf-8-*-
+// vi: set et ft=cpp ts=4 sts=4 sw=4 fenc=utf-8 :vi
+#ifndef CTL_PARTITION_H_
+#define CTL_PARTITION_H_
+#include "utility.h"
+
+namespace ctl {
+
+template<typename RandomIt, typename Compare>
+RandomIt
+partition(RandomIt first, RandomIt last, Compare comp)
+{
+    auto pivot = *ctl::move(last - 1);
+    auto i = first - 1;
+
+    for (auto j = first; j < last - 1; ++j) {
+        if (comp(*j, pivot)) {
+            ++i;
+            ctl::swap(*i, *j);
+        }
+    }
+
+    ctl::swap(*(i + 1), *(last - 1));
+    return i + 1;
+}
+
+} // namespace ctl
+
+#endif // CTL_PARTITION_H_
diff --git a/ctl/remove_cv.h b/ctl/remove_cv.h
new file mode 100644
index 000000000..2801f7d80
--- /dev/null
+++ b/ctl/remove_cv.h
@@ -0,0 +1,49 @@
+// -*-mode:c++;indent-tabs-mode:nil;c-basic-offset:4;tab-width:8;coding:utf-8-*-
+// vi: set et ft=cpp ts=4 sts=4 sw=4 fenc=utf-8 :vi
+#ifndef CTL_REMOVE_CV_H_
+#define CTL_REMOVE_CV_H_
+
+namespace ctl {
+
+template<class T>
+struct remove_const
+{
+    typedef T type;
+};
+
+template<class T>
+struct remove_const<const T>
+{
+    typedef T type;
+};
+
+template<class T>
+struct remove_volatile
+{
+    typedef T type;
+};
+
+template<class T>
+struct remove_volatile<volatile T>
+{
+    typedef T type;
+};
+
+template<class T>
+struct remove_cv
+{
+    typedef typename remove_volatile<typename remove_const<T>::type>::type type;
+};
+
+template<class T>
+using remove_const_t = typename remove_const<T>::type;
+
+template<class T>
+using remove_volatile_t = typename remove_volatile<T>::type;
+
+template<class T>
+using remove_cv_t = typename remove_cv<T>::type;
+
+} // namespace ctl
+
+#endif // CTL_REMOVE_CV_H_
diff --git a/ctl/remove_extent.h b/ctl/remove_extent.h
new file mode 100644
index 000000000..7aef1d20a
--- /dev/null
+++ b/ctl/remove_extent.h
@@ -0,0 +1,31 @@
+// -*-mode:c++;indent-tabs-mode:nil;c-basic-offset:4;tab-width:8;coding:utf-8-*-
+// vi: set et ft=cpp ts=4 sts=4 sw=4 fenc=utf-8 :vi
+#ifndef CTL_REMOVE_EXTENT_H_
+#define CTL_REMOVE_EXTENT_H_
+
+namespace ctl {
+
+template<typename T>
+struct remove_extent
+{
+    typedef T type;
+};
+
+template<typename T, size_t N>
+struct remove_extent<T[N]>
+{
+    typedef T type;
+};
+
+template<typename T>
+struct remove_extent<T[]>
+{
+    typedef T type;
+};
+
+template<typename T>
+using remove_extent_t = typename remove_extent<T>::type;
+
+} // namespace ctl
+
+#endif // CTL_REMOVE_EXTENT_H_
diff --git a/ctl/remove_reference.h b/ctl/remove_reference.h
new file mode 100644
index 000000000..3e773e0ce
--- /dev/null
+++ b/ctl/remove_reference.h
@@ -0,0 +1,31 @@
+// -*-mode:c++;indent-tabs-mode:nil;c-basic-offset:4;tab-width:8;coding:utf-8-*-
+// vi: set et ft=cpp ts=4 sts=4 sw=4 fenc=utf-8 :vi
+#ifndef CTL_REMOVE_REFERENCE_H_
+#define CTL_REMOVE_REFERENCE_H_
+
+namespace ctl {
+
+template<class T>
+struct remove_reference
+{
+    typedef T type;
+};
+
+template<class T>
+struct remove_reference<T&>
+{
+    typedef T type;
+};
+
+template<class T>
+struct remove_reference<T&&>
+{
+    typedef T type;
+};
+
+template<class T>
+using remove_reference_t = typename remove_reference<T>::type;
+
+} // namespace ctl
+
+#endif // CTL_REMOVE_REFERENCE_H_
diff --git a/ctl/runtime_error.h b/ctl/runtime_error.h
new file mode 100644
index 000000000..29cc5f301
--- /dev/null
+++ b/ctl/runtime_error.h
@@ -0,0 +1,33 @@
+// -*-mode:c++;indent-tabs-mode:nil;c-basic-offset:4;tab-width:8;coding:utf-8-*-
+// vi: set et ft=cpp ts=4 sts=4 sw=4 fenc=utf-8 :vi
+#ifndef CTL_RUNTIME_ERROR_H_
+#define CTL_RUNTIME_ERROR_H_
+#include "ctl/string.h"
+
+namespace ctl {
+
+class runtime_error
+{
+  public:
+    explicit runtime_error(const string& what_arg) : msg_(what_arg)
+    {
+    }
+
+    explicit runtime_error(const char* what_arg) : msg_(what_arg)
+    {
+    }
+
+    virtual ~runtime_error() noexcept = default;
+
+    virtual const char* what() const noexcept
+    {
+        return msg_.c_str();
+    }
+
+  private:
+    string msg_;
+};
+
+} // namespace ctl
+
+#endif // CTL_RUNTIME_ERROR_H_
diff --git a/ctl/sort.h b/ctl/sort.h
new file mode 100644
index 000000000..fb5a3d6c2
--- /dev/null
+++ b/ctl/sort.h
@@ -0,0 +1,44 @@
+// -*-mode:c++;indent-tabs-mode:nil;c-basic-offset:4;tab-width:8;coding:utf-8-*-
+// vi: set et ft=cpp ts=4 sts=4 sw=4 fenc=utf-8 :vi
+#ifndef CTL_SORT_H_
+#define CTL_SORT_H_
+#include "iterator_traits.h"
+#include "less.h"
+#include "partition.h"
+
+namespace ctl {
+
+namespace detail {
+
+template<typename RandomIt, typename Compare>
+void
+quicksort(RandomIt first, RandomIt last, Compare comp)
+{
+    if (first < last) {
+        auto pivot = ctl::partition(first, last, comp);
+        quicksort(first, pivot, comp);
+        quicksort(pivot + 1, last, comp);
+    }
+}
+
+} // namespace detail
+
+template<typename RandomIt, typename Compare>
+void
+sort(RandomIt first, RandomIt last, Compare comp)
+{
+    detail::quicksort(first, last, comp);
+}
+
+template<typename RandomIt>
+void
+sort(RandomIt first, RandomIt last)
+{
+    sort(first,
+         last,
+         ctl::less<typename ctl::iterator_traits<RandomIt>::value_type>());
+}
+
+} // namespace ctl
+
+#endif // CTL_SORT_H_
diff --git a/ctl/strcat.cc b/ctl/strcat.cc
index 0e7c49070..a00cf0e59 100644
--- a/ctl/strcat.cc
+++ b/ctl/strcat.cc
@@ -38,9 +38,9 @@ strcat(const string_view lhs, const string_view rhs) noexcept
     if (rhs.n)
         memcpy(res.data() + lhs.n, rhs.p, rhs.n);
     if (res.isbig()) {
-        res.big()->n = lhs.n + rhs.n;
+        res.__b.n = lhs.n + rhs.n;
     } else {
-        res.small()->rem = __::sso_max - lhs.n - rhs.n;
+        res.__s.rem = __::sso_max - lhs.n - rhs.n;
     }
     res.data()[res.size()] = 0;
     return res;
diff --git a/ctl/string.cc b/ctl/string.cc
index 08ee1e65d..064882178 100644
--- a/ctl/string.cc
+++ b/ctl/string.cc
@@ -26,7 +26,7 @@ namespace ctl {
 void
 string::destroy_big() noexcept
 {
-    auto* b = big();
+    auto* b = &__b;
     if (b->n) {
         if (b->n >= b->c)
             __builtin_trap();
@@ -41,7 +41,14 @@ string::destroy_big() noexcept
 void
 string::init_big(const string& s) noexcept
 {
-    init_big(string_view(s));
+    char* p2;
+    size_t size = s.size();
+    size_t need = size + 1;
+    size_t capacity = need;
+    if (!(p2 = (char*)malloc(capacity)))
+        __builtin_trap();
+    memcpy(p2, s.data(), need);
+    set_big_string(p2, size, capacity);
 }
 
 void
@@ -103,7 +110,7 @@ string::reserve(size_t c2) noexcept
             __builtin_trap();
         memcpy(p2, data(), __::string_size);
     } else {
-        if (!(p2 = (char*)realloc(big()->p, c2)))
+        if (!(p2 = (char*)realloc(__b.p, c2)))
             __builtin_trap();
     }
     std::atomic_signal_fence(std::memory_order_seq_cst);
@@ -120,7 +127,7 @@ string::resize(const size_t n2, const char ch) noexcept
     if (n2 > size())
         memset(data() + size(), ch, n2 - size());
     if (isbig()) {
-        big()->p[big()->n = n2] = 0;
+        __b.p[__b.n = n2] = 0;
     } else {
         set_small_size(n2);
         data()[size()] = 0;
@@ -141,9 +148,9 @@ string::append(const char ch) noexcept
     }
     data()[size()] = ch;
     if (isbig()) {
-        ++big()->n;
+        ++__b.n;
     } else {
-        --small()->rem;
+        --__s.rem;
     }
     data()[size()] = 0;
 }
@@ -174,9 +181,9 @@ string::append(const char ch, const size_t size) noexcept
     if (size)
         memset(data() + this->size(), ch, size);
     if (isbig()) {
-        big()->n += size;
+        __b.n += size;
     } else {
-        small()->rem -= size;
+        __s.rem -= size;
     }
     data()[this->size()] = 0;
 }
@@ -188,9 +195,9 @@ string::append(const void* data, const size_t size) noexcept
     if (size)
         memcpy(this->data() + this->size(), data, size);
     if (isbig()) {
-        big()->n += size;
+        __b.n += size;
     } else {
-        small()->rem -= size;
+        __s.rem -= size;
     }
     this->data()[this->size()] = 0;
 }
@@ -201,9 +208,9 @@ string::pop_back() noexcept
     if (!size())
         __builtin_trap();
     if (isbig()) {
-        --big()->n;
+        --__b.n;
     } else {
-        ++small()->rem;
+        ++__s.rem;
     }
     data()[size()] = 0;
 }
@@ -322,7 +329,7 @@ string::replace(const size_t pos,
         memmove(data() + pos + s.n, data() + last, extra);
     memcpy(data() + pos, s.p, s.n);
     if (isbig()) {
-        big()->p[big()->n = need] = 0;
+        __b.p[__b.n = need] = 0;
     } else {
         set_small_size(need);
         data()[size()] = 0;
@@ -346,9 +353,9 @@ string::insert(const size_t i, const string_view s) noexcept
         memmove(data() + i + s.n, data() + i, extra);
     memcpy(data() + i, s.p, s.n);
     if (isbig()) {
-        big()->n += s.n;
+        __b.n += s.n;
     } else {
-        small()->rem -= s.n;
+        __s.rem -= s.n;
     }
     data()[size()] = 0;
     return *this;
@@ -365,7 +372,7 @@ string::erase(const size_t pos, size_t count) noexcept
     if (extra)
         memmove(data() + pos, data() + pos + count, extra);
     if (isbig()) {
-        big()->n = pos + extra;
+        __b.n = pos + extra;
     } else {
         set_small_size(pos + extra);
     }
diff --git a/ctl/string.h b/ctl/string.h
index 69a9cf1b7..ba0ee6223 100644
--- a/ctl/string.h
+++ b/ctl/string.h
@@ -151,7 +151,7 @@ class string
     void clear() noexcept
     {
         if (isbig()) {
-            big()->n = 0;
+            __b.n = 0;
         } else {
             set_small_size(0);
         }
@@ -159,26 +159,26 @@ class string
 
     bool empty() const noexcept
     {
-        return isbig() ? !big()->n : small()->rem >= __::sso_max;
+        return isbig() ? !__b.n : __s.rem >= __::sso_max;
     }
 
-    char* data() noexcept
+    __attribute__((__always_inline__)) char* data() noexcept
     {
-        return isbig() ? big()->p : small()->buf;
+        return isbig() ? __b.p : __s.buf;
     }
 
-    const char* data() const noexcept
+    __attribute__((__always_inline__)) const char* data() const noexcept
     {
-        return isbig() ? big()->p : small()->buf;
+        return isbig() ? __b.p : __s.buf;
     }
 
-    size_t size() const noexcept
+    __attribute__((__always_inline__)) size_t size() const noexcept
     {
 #if 0
-        if (!isbig() && small()->rem > __::sso_max)
+        if (!isbig() && __s.rem > __::sso_max)
             __builtin_trap();
 #endif
-        return isbig() ? big()->n : __::sso_max - small()->rem;
+        return isbig() ? __b.n : __::sso_max - __s.rem;
     }
 
     size_t length() const noexcept
@@ -189,10 +189,10 @@ class string
     size_t capacity() const noexcept
     {
 #if 0
-        if (isbig() && big()->c <= __::sso_max)
+        if (isbig() && __b.c <= __::sso_max)
             __builtin_trap();
 #endif
-        return isbig() ? __::big_mask & big()->c : __::string_size;
+        return isbig() ? __::big_mask & __b.c : __::string_size;
     }
 
     iterator begin() noexcept
@@ -374,7 +374,7 @@ class string
     void init_big(string_view) noexcept;
     void init_big(size_t, char) noexcept;
 
-    bool isbig() const noexcept
+    __attribute__((__always_inline__)) bool isbig() const noexcept
     {
         return *(blob + __::sso_max) & 0x80;
     }
@@ -395,34 +395,6 @@ class string
         __b.c = c2 | ~__::big_mask;
     }
 
-    __::small_string* small() noexcept
-    {
-        if (isbig())
-            __builtin_trap();
-        return &__s;
-    }
-
-    const __::small_string* small() const noexcept
-    {
-        if (isbig())
-            __builtin_trap();
-        return &__s;
-    }
-
-    __::big_string* big() noexcept
-    {
-        if (!isbig())
-            __builtin_trap();
-        return &__b;
-    }
-
-    const __::big_string* big() const noexcept
-    {
-        if (!isbig())
-            __builtin_trap();
-        return &__b;
-    }
-
     friend string strcat(string_view, string_view) noexcept;
 
     union
diff --git a/ctl/tuple.h b/ctl/tuple.h
new file mode 100644
index 000000000..dcea0f15f
--- /dev/null
+++ b/ctl/tuple.h
@@ -0,0 +1,138 @@
+// -*-mode:c++;indent-tabs-mode:nil;c-basic-offset:4;tab-width:8;coding:utf-8-*-
+// vi: set et ft=cpp ts=4 sts=4 sw=4 fenc=utf-8 :vi
+#ifndef CTL_TUPLE_H_
+#define CTL_TUPLE_H_
+#include "decay.h"
+#include "enable_if.h"
+#include "is_same.h"
+#include "utility.h"
+
+namespace ctl {
+
+// Forward declaration
+template<typename... Types>
+class tuple;
+
+// Base case for tuple
+template<>
+class tuple<>
+{};
+
+// Recursive case for tuple
+template<typename Head, typename... Tail>
+class tuple<Head, Tail...> : public tuple<Tail...>
+{
+    using Base = tuple<Tail...>;
+
+  public:
+    Head head;
+
+    constexpr tuple() : Base(), head()
+    {
+    }
+
+    template<typename H,
+             typename... T,
+             typename = typename ctl::enable_if<
+               !ctl::is_same<typename ctl::decay<H>::type, tuple>::value>::type>
+    constexpr tuple(H&& h, T&&... t)
+      : Base(ctl::forward<T>(t)...), head(ctl::forward<H>(h))
+    {
+    }
+
+    template<typename... UTypes>
+    constexpr tuple(const tuple<UTypes...>& other)
+      : Base(static_cast<const tuple<UTypes...>&>(other)), head(other.head)
+    {
+    }
+
+    template<typename... UTypes>
+    constexpr tuple(tuple<UTypes...>&& other)
+      : Base(static_cast<tuple<UTypes...>&&>(other))
+      , head(ctl::forward<Head>(other.head))
+    {
+    }
+
+    tuple(const tuple&) = default;
+    tuple(tuple&&) = default;
+    tuple& operator=(const tuple&) = default;
+    tuple& operator=(tuple&&) = default;
+};
+
+// Helper struct for getting element type
+template<size_t I, typename T>
+struct tuple_element;
+
+template<size_t I, typename Head, typename... Tail>
+struct tuple_element<I, tuple<Head, Tail...>>
+  : tuple_element<I - 1, tuple<Tail...>>
+{};
+
+template<typename Head, typename... Tail>
+struct tuple_element<0, tuple<Head, Tail...>>
+{
+    using type = Head;
+};
+
+// Helper function to get element
+template<size_t I, typename Head, typename... Tail>
+constexpr typename tuple_element<I, tuple<Head, Tail...>>::type&
+get(tuple<Head, Tail...>& t)
+{
+    if constexpr (I == 0) {
+        return t.head;
+    } else {
+        return get<I - 1>(static_cast<tuple<Tail...>&>(t));
+    }
+}
+
+template<size_t I, typename Head, typename... Tail>
+constexpr const typename tuple_element<I, tuple<Head, Tail...>>::type&
+get(const tuple<Head, Tail...>& t)
+{
+    if constexpr (I == 0) {
+        return t.head;
+    } else {
+        return get<I - 1>(static_cast<const tuple<Tail...>&>(t));
+    }
+}
+
+// Helper function to create a tuple
+template<typename... Types>
+constexpr tuple<typename ctl::decay<Types>::type...>
+make_tuple(Types&&... args)
+{
+    return tuple<typename ctl::decay<Types>::type...>(
+      ctl::forward<Types>(args)...);
+}
+
+// Helper function for tuple comparison
+template<size_t I = 0, typename... TTypes, typename... UTypes>
+constexpr bool
+tuple_equals(const tuple<TTypes...>& t, const tuple<UTypes...>& u)
+{
+    if constexpr (I == sizeof...(TTypes)) {
+        return true;
+    } else {
+        return get<I>(t) == get<I>(u) && tuple_equals<I + 1>(t, u);
+    }
+}
+
+// Equality comparison
+template<typename... TTypes, typename... UTypes>
+constexpr bool
+operator==(const tuple<TTypes...>& t, const tuple<UTypes...>& u)
+{
+    return tuple_equals(t, u);
+}
+
+template<typename... TTypes, typename... UTypes>
+constexpr bool
+operator!=(const tuple<TTypes...>& t, const tuple<UTypes...>& u)
+{
+    return !(t == u);
+}
+
+} // namespace ctl
+
+#endif // CTL_TUPLE_H_
diff --git a/ctl/unique_lock.h b/ctl/unique_lock.h
new file mode 100644
index 000000000..6568a408e
--- /dev/null
+++ b/ctl/unique_lock.h
@@ -0,0 +1,147 @@
+// -*-mode:c++;indent-tabs-mode:nil;c-basic-offset:4;tab-width:8;coding:utf-8-*-
+// vi: set et ft=cpp ts=4 sts=4 sw=4 fenc=utf-8 :vi
+#ifndef CTL_UNIQUE_LOCK_H_
+#define CTL_UNIQUE_LOCK_H_
+#include "mutex.h"
+#include "utility.h"
+
+namespace ctl {
+
+struct defer_lock_t
+{
+    explicit defer_lock_t() = default;
+};
+
+struct try_to_lock_t
+{
+    explicit try_to_lock_t() = default;
+};
+
+struct adopt_lock_t
+{
+    explicit adopt_lock_t() = default;
+};
+
+inline constexpr defer_lock_t defer_lock{};
+inline constexpr try_to_lock_t try_to_lock{};
+inline constexpr adopt_lock_t adopt_lock{};
+
+class unique_lock
+{
+  public:
+    unique_lock() noexcept : mutex_(nullptr), owns_lock_(false)
+    {
+    }
+
+    explicit unique_lock(ctl::mutex& m) : mutex_(&m), owns_lock_(false)
+    {
+        lock();
+    }
+
+    unique_lock(ctl::mutex& m, defer_lock_t) noexcept
+      : mutex_(&m), owns_lock_(false)
+    {
+    }
+
+    unique_lock(ctl::mutex& m, try_to_lock_t)
+      : mutex_(&m), owns_lock_(mutex_->try_lock())
+    {
+    }
+
+    unique_lock(ctl::mutex& m, adopt_lock_t) : mutex_(&m), owns_lock_(true)
+    {
+    }
+
+    ~unique_lock()
+    {
+        if (owns_lock_)
+            mutex_->unlock();
+    }
+
+    unique_lock(const unique_lock&) = delete;
+    unique_lock& operator=(const unique_lock&) = delete;
+
+    unique_lock(unique_lock&& other) noexcept
+      : mutex_(other.mutex_), owns_lock_(other.owns_lock_)
+    {
+        other.mutex_ = nullptr;
+        other.owns_lock_ = false;
+    }
+
+    unique_lock& operator=(unique_lock&& other) noexcept
+    {
+        if (owns_lock_)
+            mutex_->unlock();
+        mutex_ = other.mutex_;
+        owns_lock_ = other.owns_lock_;
+        other.mutex_ = nullptr;
+        other.owns_lock_ = false;
+        return *this;
+    }
+
+    void lock()
+    {
+        if (!mutex_)
+            __builtin_trap();
+        if (owns_lock_)
+            __builtin_trap();
+        mutex_->lock();
+        owns_lock_ = true;
+    }
+
+    bool try_lock()
+    {
+        if (!mutex_)
+            __builtin_trap();
+        if (owns_lock_)
+            __builtin_trap();
+        owns_lock_ = mutex_->try_lock();
+        return owns_lock_;
+    }
+
+    void unlock()
+    {
+        if (!owns_lock_)
+            __builtin_trap();
+        mutex_->unlock();
+        owns_lock_ = false;
+    }
+
+    void swap(unique_lock& other) noexcept
+    {
+        using ctl::swap;
+        swap(mutex_, other.mutex_);
+        swap(owns_lock_, other.owns_lock_);
+    }
+
+    ctl::mutex* release() noexcept
+    {
+        ctl::mutex* result = mutex_;
+        mutex_ = nullptr;
+        owns_lock_ = false;
+        return result;
+    }
+
+    bool owns_lock() const noexcept
+    {
+        return owns_lock_;
+    }
+
+    explicit operator bool() const noexcept
+    {
+        return owns_lock_;
+    }
+
+    ctl::mutex* mutex() const noexcept
+    {
+        return mutex_;
+    }
+
+  private:
+    ctl::mutex* mutex_;
+    bool owns_lock_;
+};
+
+} // namespace ctl
+
+#endif // CTL_UNIQUE_LOCK_H_
diff --git a/ctl/unique_ptr.cc b/ctl/unique_ptr.cc
deleted file mode 100644
index daeda3b1b..000000000
--- a/ctl/unique_ptr.cc
+++ /dev/null
@@ -1,19 +0,0 @@
-// -*- mode:c++; indent-tabs-mode:nil; c-basic-offset:4; coding:utf-8 -*-
-// vi: set et ft=cpp ts=4 sts=4 sw=4 fenc=utf-8 :vi
-//
-// Copyright 2024 Justine Alexandra Roberts Tunney
-//
-// Permission to use, copy, modify, and/or distribute this software for
-// any purpose with or without fee is hereby granted, provided that the
-// above copyright notice and this permission notice appear in all copies.
-//
-// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL
-// WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED
-// WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE
-// AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
-// DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
-// PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
-// TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
-// PERFORMANCE OF THIS SOFTWARE.
-
-#include "unique_ptr.h"
diff --git a/ctl/unique_ptr.h b/ctl/unique_ptr.h
index c2ebae7ba..5027d5ec1 100644
--- a/ctl/unique_ptr.h
+++ b/ctl/unique_ptr.h
@@ -1,41 +1,17 @@
 // -*-mode:c++;indent-tabs-mode:nil;c-basic-offset:4;tab-width:8;coding:utf-8-*-
 // vi: set et ft=cpp ts=4 sts=4 sw=4 fenc=utf-8 :vi
-#ifndef COSMOPOLITAN_CTL_UNIQUE_PTR_H_
-#define COSMOPOLITAN_CTL_UNIQUE_PTR_H_
+#ifndef CTL_UNIQUE_PTR_H_
+#define CTL_UNIQUE_PTR_H_
+#include "add_lvalue_reference.h"
+#include "default_delete.h"
+#include "is_convertible.h"
+#include "is_reference.h"
+#include "is_same.h"
 #include "utility.h"
-#include <__type_traits/is_convertible.h>
 
 namespace ctl {
 
-template<typename T>
-struct default_delete
-{
-    constexpr default_delete() noexcept = default;
-    template<typename U>
-    constexpr default_delete(default_delete<U>&&) noexcept
-    {
-    }
-    constexpr void operator()(T* const p) const noexcept
-    {
-        delete p;
-    }
-};
-
-template<typename T>
-struct default_delete<T[]>
-{
-    constexpr default_delete() noexcept = default;
-    template<typename U>
-    constexpr default_delete(default_delete<U>&&) noexcept
-    {
-    }
-    constexpr void operator()(T* const p) const noexcept
-    {
-        delete[] p;
-    }
-};
-
-template<typename T, typename D = default_delete<T>>
+template<typename T, typename D = ctl::default_delete<T>>
 struct unique_ptr
 {
     using pointer = T*;
@@ -49,26 +25,34 @@ struct unique_ptr
     {
     }
 
-    constexpr unique_ptr(const pointer p) noexcept : p(p), d()
+    constexpr explicit unique_ptr(pointer p) noexcept : p(p), d()
     {
     }
 
-    constexpr unique_ptr(const pointer p, auto&& d) noexcept
-      : p(p), d(ctl::forward<decltype(d)>(d))
+    constexpr unique_ptr(pointer p, const D& d) noexcept : p(p), d(d)
+    {
+    }
+
+    constexpr unique_ptr(pointer p, D&& d) noexcept : p(p), d(ctl::move(d))
     {
     }
 
     template<typename U, typename E>
-        requires std::is_convertible_v<U, T> && std::is_convertible_v<E, D>
     constexpr unique_ptr(unique_ptr<U, E>&& u) noexcept
-      : p(u.p), d(ctl::move(u.d))
+      : p(u.release()), d(ctl::forward<E>(u.get_deleter()))
     {
-        u.p = nullptr;
+        static_assert(ctl::is_convertible<typename unique_ptr<U, E>::pointer,
+                                          pointer>::value,
+                      "U* must be implicitly convertible to T*");
+        static_assert(
+          (ctl::is_reference<D>::value && ctl::is_same<D, E>::value) ||
+            (!ctl::is_reference<D>::value && ctl::is_convertible<E, D>::value),
+          "The deleter must be convertible to the target deleter type");
     }
 
     unique_ptr(const unique_ptr&) = delete;
 
-    constexpr ~unique_ptr() /* noexcept */
+    constexpr ~unique_ptr() noexcept
     {
         if (p)
             d(p);
@@ -80,6 +64,20 @@ struct unique_ptr
         return *this;
     }
 
+    template<typename U, typename E>
+    constexpr unique_ptr& operator=(unique_ptr<U, E>&& r) noexcept
+    {
+        reset(r.release());
+        d = ctl::forward<E>(r.get_deleter());
+        return *this;
+    }
+
+    constexpr unique_ptr& operator=(nullptr_t) noexcept
+    {
+        reset();
+        return *this;
+    }
+
     constexpr pointer release() noexcept
     {
         pointer r = p;
@@ -87,12 +85,12 @@ struct unique_ptr
         return r;
     }
 
-    constexpr void reset(const pointer p2 = pointer()) noexcept
+    constexpr void reset(pointer p2 = pointer()) noexcept
     {
-        const pointer r = p;
+        pointer old = p;
         p = p2;
-        if (r)
-            d(r);
+        if (old)
+            d(old);
     }
 
     constexpr void swap(unique_ptr& r) noexcept
@@ -119,20 +117,16 @@ struct unique_ptr
 
     constexpr explicit operator bool() const noexcept
     {
-        return p;
+        return p != nullptr;
     }
 
-    element_type& operator*() const noexcept(noexcept(*ctl::declval<pointer>()))
+    constexpr typename ctl::add_lvalue_reference<T>::type operator*() const
     {
-        if (!p)
-            __builtin_trap();
         return *p;
     }
 
-    pointer operator->() const noexcept
+    constexpr pointer operator->() const noexcept
     {
-        if (!p)
-            __builtin_trap();
         return p;
     }
 };
@@ -148,16 +142,9 @@ template<typename T>
 constexpr unique_ptr<T>
 make_unique_for_overwrite()
 {
-#if 0
-    // You'd think that it'd work like this, but std::unique_ptr does not.
-    return unique_ptr<T>(
-      static_cast<T*>(::operator new(sizeof(T), align_val_t(alignof(T)))));
-#else
     return unique_ptr<T>(new T);
-#endif
 }
 
-// TODO(mrdomino): specializations for T[]
-
 } // namespace ctl
-#endif // COSMOPOLITAN_CTL_UNIQUE_PTR_H_
+
+#endif // CTL_UNIQUE_PTR_H_
diff --git a/ctl/utility.cc b/ctl/utility.cc
deleted file mode 100644
index a4c2a2008..000000000
--- a/ctl/utility.cc
+++ /dev/null
@@ -1,19 +0,0 @@
-// -*- mode:c++; indent-tabs-mode:nil; c-basic-offset:4; coding:utf-8 -*-
-// vi: set et ft=cpp ts=4 sts=4 sw=4 fenc=utf-8 :vi
-//
-// Copyright 2024 Justine Alexandra Roberts Tunney
-//
-// Permission to use, copy, modify, and/or distribute this software for
-// any purpose with or without fee is hereby granted, provided that the
-// above copyright notice and this permission notice appear in all copies.
-//
-// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL
-// WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED
-// WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE
-// AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
-// DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
-// PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
-// TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
-// PERFORMANCE OF THIS SOFTWARE.
-
-#include "utility.h"
diff --git a/ctl/utility.h b/ctl/utility.h
index 62036ca04..464e04f64 100644
--- a/ctl/utility.h
+++ b/ctl/utility.h
@@ -2,6 +2,7 @@
 // vi: set et ft=cpp ts=4 sts=4 sw=4 fenc=utf-8 :vi
 #ifndef COSMOPOLITAN_CTL_UTILITY_H_
 #define COSMOPOLITAN_CTL_UTILITY_H_
+#include "remove_reference.h"
 
 namespace ctl {
 
@@ -18,6 +19,14 @@ using no_infer = typename no_infer_<T>::type;
 
 } // namespace __
 
+template<typename T>
+constexpr T&&
+move(T&& t) noexcept
+{
+    typedef remove_reference_t<T> U;
+    return static_cast<U&&>(t);
+}
+
 template<typename T>
 constexpr T&&
 move(T& t) noexcept
@@ -47,9 +56,8 @@ template<typename T, size_t N>
 constexpr void
 swap(T (&a)[N], T (&b)[N]) noexcept
 {
-    for (size_t i = 0; i < N; ++i) {
+    for (size_t i = 0; i < N; ++i)
         swap(a[i], b[i]);
-    }
 }
 
 template<typename T>
diff --git a/ctl/void_t.h b/ctl/void_t.h
new file mode 100644
index 000000000..c4573260e
--- /dev/null
+++ b/ctl/void_t.h
@@ -0,0 +1,13 @@
+// -*-mode:c++;indent-tabs-mode:nil;c-basic-offset:4;tab-width:8;coding:utf-8-*-
+// vi: set et ft=cpp ts=4 sts=4 sw=4 fenc=utf-8 :vi
+#ifndef CTL_VOID_T_H_
+#define CTL_VOID_T_H_
+
+namespace ctl {
+
+template<typename... Ts>
+using void_t = void;
+
+} // namespace ctl
+
+#endif // CTL_VOID_T_H_
diff --git a/libc/runtime/dsohandle.S b/libc/intrin/dsohandle.S
similarity index 100%
rename from libc/runtime/dsohandle.S
rename to libc/intrin/dsohandle.S
diff --git a/test/ctl/BUILD.mk b/test/ctl/BUILD.mk
index 439d7e786..2bdcf5381 100644
--- a/test/ctl/BUILD.mk
+++ b/test/ctl/BUILD.mk
@@ -18,6 +18,7 @@ TEST_CTL_DIRECTDEPS =				\
 	LIBC_INTRIN				\
 	LIBC_MEM				\
 	LIBC_STDIO				\
+	LIBC_THREAD				\
 	THIRD_PARTY_LIBCXX			\
 	THIRD_PARTY_LIBCXXABI			\
 	THIRD_PARTY_LIBUNWIND			\
diff --git a/test/ctl/accumulate_test.cc b/test/ctl/accumulate_test.cc
index ff29e278e..3145e18e2 100644
--- a/test/ctl/accumulate_test.cc
+++ b/test/ctl/accumulate_test.cc
@@ -18,6 +18,7 @@
 
 #include "ctl/accumulate.h"
 #include "ctl/array.h"
+#include "libc/mem/leaks.h"
 
 // #include <array>
 // #include <numeric>
@@ -48,4 +49,6 @@ main()
     // Test accumulation with single element
     if (ctl::accumulate(arr.begin(), arr.begin() + 1, 0) != 1)
         return 5;
+
+    CheckForMemoryLeaks();
 }
diff --git a/test/ctl/advance_test.cc b/test/ctl/advance_test.cc
index 90b381bd5..e0782ba35 100644
--- a/test/ctl/advance_test.cc
+++ b/test/ctl/advance_test.cc
@@ -18,6 +18,7 @@
 
 #include "ctl/advance.h"
 #include "ctl/array.h"
+#include "libc/mem/leaks.h"
 
 // #include <array>
 // #include <iterator>
@@ -53,4 +54,6 @@ main()
     ctl::advance(it, -2);
     if (it != arr.begin())
         return 5;
+
+    CheckForMemoryLeaks();
 }
diff --git a/test/ctl/all_of_test.cc b/test/ctl/all_of_test.cc
index 5f38e441b..4bc090b67 100644
--- a/test/ctl/all_of_test.cc
+++ b/test/ctl/all_of_test.cc
@@ -18,6 +18,7 @@
 
 #include "ctl/all_of.h"
 #include "ctl/array.h"
+#include "libc/mem/leaks.h"
 
 #include <algorithm>
 #include <array>
@@ -49,4 +50,6 @@ main()
     // Test with no elements satisfying the condition
     if (ctl::all_of(arr1.begin(), arr1.end(), [](int n) { return n > 10; }))
         return 5;
+
+    CheckForMemoryLeaks();
 }
diff --git a/test/ctl/any_of_test.cc b/test/ctl/any_of_test.cc
index 02ba6928d..ee08afd3e 100644
--- a/test/ctl/any_of_test.cc
+++ b/test/ctl/any_of_test.cc
@@ -18,6 +18,7 @@
 
 #include "ctl/any_of.h"
 #include "ctl/array.h"
+#include "libc/mem/leaks.h"
 
 // #include <algorithm>
 // #include <array>
@@ -48,4 +49,6 @@ main()
     // Test with a different condition
     if (!ctl::any_of(arr1.begin(), arr1.end(), [](int n) { return n > 5; }))
         return 5;
+
+    CheckForMemoryLeaks();
 }
diff --git a/test/ctl/array_test.cc b/test/ctl/array_test.cc
index 5fd8dbe54..40f774173 100644
--- a/test/ctl/array_test.cc
+++ b/test/ctl/array_test.cc
@@ -17,8 +17,11 @@
 // PERFORMANCE OF THIS SOFTWARE.
 
 #include "ctl/array.h"
+#include "ctl/string.h"
+#include "libc/mem/leaks.h"
 
 // #include <array>
+// #include <string>
 // #define ctl std
 
 int
@@ -264,4 +267,21 @@ main()
         if (rit != arr.rend())
             return 4;
     }
+
+    {
+        ctl::array<ctl::string, 2> A = { "hi", "theretheretheretherethere" };
+        if (A.size() != 2)
+            return 76;
+        if (A[0] != "hi")
+            return 77;
+        if (A[1] != "theretheretheretherethere")
+            return 78;
+        A = { "theretheretheretherethere", "hi" };
+        if (A[0] != "theretheretheretherethere")
+            return 79;
+        if (A[1] != "hi")
+            return 80;
+    }
+
+    CheckForMemoryLeaks();
 }
diff --git a/test/ctl/back_inserter_test.cc b/test/ctl/back_inserter_test.cc
index 38659b10e..122493952 100644
--- a/test/ctl/back_inserter_test.cc
+++ b/test/ctl/back_inserter_test.cc
@@ -20,6 +20,7 @@
 #include "ctl/back_inserter.h"
 #include "ctl/copy.h"
 #include "ctl/vector.h"
+#include "libc/mem/leaks.h"
 
 // #include <array>
 // #include <iterator>
@@ -29,33 +30,38 @@
 int
 main()
 {
-    ctl::vector<int> vec = { 1, 2, 3 };
-    ctl::array<int, 3> arr = { 4, 5, 6 };
 
-    // Use back_inserter to append elements from arr to vec
-    ctl::copy(arr.begin(), arr.end(), ctl::back_inserter(vec));
+    {
+        ctl::vector<int> vec = { 1, 2, 3 };
+        ctl::array<int, 3> arr = { 4, 5, 6 };
 
-    // Check if vec now contains all elements
-    if (vec.size() != 6)
-        return 1;
-    if (vec[0] != 1 || vec[1] != 2 || vec[2] != 3 || vec[3] != 4 ||
-        vec[4] != 5 || vec[5] != 6)
-        return 2;
+        // Use back_inserter to append elements from arr to vec
+        ctl::copy(arr.begin(), arr.end(), ctl::back_inserter(vec));
 
-    // Use back_inserter with a single element
-    ctl::back_inserter(vec) = 7;
+        // Check if vec now contains all elements
+        if (vec.size() != 6)
+            return 1;
+        if (vec[0] != 1 || vec[1] != 2 || vec[2] != 3 || vec[3] != 4 ||
+            vec[4] != 5 || vec[5] != 6)
+            return 2;
 
-    // Check if the new element was added
-    if (vec.size() != 7)
-        return 3;
-    if (vec[6] != 7)
-        return 4;
+        // Use back_inserter with a single element
+        ctl::back_inserter(vec) = 7;
 
-    // Test with an empty source range
-    ctl::array<int, 0> empty_arr;
-    ctl::copy(empty_arr.begin(), empty_arr.end(), ctl::back_inserter(vec));
+        // Check if the new element was added
+        if (vec.size() != 7)
+            return 3;
+        if (vec[6] != 7)
+            return 4;
 
-    // Check that no elements were added
-    if (vec.size() != 7)
-        return 5;
+        // Test with an empty source range
+        ctl::array<int, 0> empty_arr;
+        ctl::copy(empty_arr.begin(), empty_arr.end(), ctl::back_inserter(vec));
+
+        // Check that no elements were added
+        if (vec.size() != 7)
+            return 5;
+    }
+
+    CheckForMemoryLeaks();
 }
diff --git a/test/ctl/copy_test.cc b/test/ctl/copy_test.cc
index 868bbee97..2c417186a 100644
--- a/test/ctl/copy_test.cc
+++ b/test/ctl/copy_test.cc
@@ -18,49 +18,56 @@
 
 #include "ctl/array.h"
 #include "ctl/copy.h"
+#include "libc/mem/leaks.h"
 
-// #include <iterator>
+// #include <algorithm>
 // #include <array>
+// #include <iterator>
 // #define ctl std
 
 int
 main()
 {
-    ctl::array<int, 5> src = { 1, 2, 3, 4, 5 };
-    ctl::array<int, 5> dest = { 0, 0, 0, 0, 0 };
 
-    // Test basic copy
-    ctl::copy(src.begin(), src.end(), dest.begin());
-    for (size_t i = 0; i < 5; ++i) {
-        if (dest[i] != src[i])
-            return 1;
+    {
+        ctl::array<int, 5> src = { 1, 2, 3, 4, 5 };
+        ctl::array<int, 5> dest = { 0, 0, 0, 0, 0 };
+
+        // Test basic copy
+        ctl::copy(src.begin(), src.end(), dest.begin());
+        for (size_t i = 0; i < 5; ++i) {
+            if (dest[i] != src[i])
+                return 1;
+        }
+
+        // Test partial copy
+        ctl::array<int, 5> dest2 = { 0, 0, 0, 0, 0 };
+        ctl::copy(src.begin(), src.begin() + 3, dest2.begin());
+        if (dest2[0] != 1 || dest2[1] != 2 || dest2[2] != 3 || dest2[3] != 0 ||
+            dest2[4] != 0)
+            return 2;
+
+        // Test copy to middle of destination
+        ctl::array<int, 7> dest3 = { 0, 0, 0, 0, 0, 0, 0 };
+        ctl::copy(src.begin(), src.end(), dest3.begin() + 1);
+        if (dest3[0] != 0 || dest3[1] != 1 || dest3[2] != 2 || dest3[3] != 3 ||
+            dest3[4] != 4 || dest3[5] != 5 || dest3[6] != 0)
+            return 3;
+
+        // Test copy with empty range
+        ctl::array<int, 5> dest4 = { 0, 0, 0, 0, 0 };
+        ctl::copy(src.begin(), src.begin(), dest4.begin());
+        for (size_t i = 0; i < 5; ++i) {
+            if (dest4[i] != 0)
+                return 4;
+        }
+
+        // Test copy return value
+        ctl::array<int, 5> dest5 = { 0, 0, 0, 0, 0 };
+        auto result = ctl::copy(src.begin(), src.end(), dest5.begin());
+        if (result != dest5.end())
+            return 5;
     }
 
-    // Test partial copy
-    ctl::array<int, 5> dest2 = { 0, 0, 0, 0, 0 };
-    ctl::copy(src.begin(), src.begin() + 3, dest2.begin());
-    if (dest2[0] != 1 || dest2[1] != 2 || dest2[2] != 3 || dest2[3] != 0 ||
-        dest2[4] != 0)
-        return 2;
-
-    // Test copy to middle of destination
-    ctl::array<int, 7> dest3 = { 0, 0, 0, 0, 0, 0, 0 };
-    ctl::copy(src.begin(), src.end(), dest3.begin() + 1);
-    if (dest3[0] != 0 || dest3[1] != 1 || dest3[2] != 2 || dest3[3] != 3 ||
-        dest3[4] != 4 || dest3[5] != 5 || dest3[6] != 0)
-        return 3;
-
-    // Test copy with empty range
-    ctl::array<int, 5> dest4 = { 0, 0, 0, 0, 0 };
-    ctl::copy(src.begin(), src.begin(), dest4.begin());
-    for (size_t i = 0; i < 5; ++i) {
-        if (dest4[i] != 0)
-            return 4;
-    }
-
-    // Test copy return value
-    ctl::array<int, 5> dest5 = { 0, 0, 0, 0, 0 };
-    auto result = ctl::copy(src.begin(), src.end(), dest5.begin());
-    if (result != dest5.end())
-        return 5;
+    CheckForMemoryLeaks();
 }
diff --git a/test/ctl/mutex_test.cc b/test/ctl/mutex_test.cc
new file mode 100644
index 000000000..9c03d08c8
--- /dev/null
+++ b/test/ctl/mutex_test.cc
@@ -0,0 +1,114 @@
+// -*- mode:c++; indent-tabs-mode:nil; c-basic-offset:4; coding:utf-8 -*-
+// vi: set et ft=cpp ts=4 sts=4 sw=4 fenc=utf-8 :vi
+//
+// Copyright 2024 Justine Alexandra Roberts Tunney
+//
+// Permission to use, copy, modify, and/or distribute this software for
+// any purpose with or without fee is hereby granted, provided that the
+// above copyright notice and this permission notice appear in all copies.
+//
+// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL
+// WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED
+// WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE
+// AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
+// DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
+// PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
+// TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+// PERFORMANCE OF THIS SOFTWARE.
+
+#include "ctl/mutex.h"
+#include "libc/mem/leaks.h"
+
+// #include <mutex>
+// #define ctl std
+
+ctl::mutex mtx;
+int shared_resource = 0;
+const int NUM_THREADS = 5;
+const int ITERATIONS = 100000;
+
+void*
+increment_resource(void* arg)
+{
+    for (int i = 0; i < ITERATIONS; ++i) {
+        mtx.lock();
+        ++shared_resource;
+        mtx.unlock();
+    }
+    return nullptr;
+}
+
+void*
+decrement_resource(void* arg)
+{
+    for (int i = 0; i < ITERATIONS; ++i) {
+        mtx.lock();
+        --shared_resource;
+        mtx.unlock();
+    }
+    return nullptr;
+}
+
+int
+test_basic_locking()
+{
+    shared_resource = 0;
+    pthread_t threads[NUM_THREADS];
+    for (int i = 0; i < NUM_THREADS; ++i)
+        if (pthread_create(&threads[i], 0, increment_resource, 0) != 0)
+            return 1;
+    for (int i = 0; i < NUM_THREADS; ++i)
+        if (pthread_join(threads[i], 0) != 0)
+            return 2;
+    return (shared_resource == NUM_THREADS * ITERATIONS) ? 0 : 3;
+}
+
+int
+test_lock_contention()
+{
+    shared_resource = 0;
+    pthread_t threads[NUM_THREADS * 2];
+    for (int i = 0; i < NUM_THREADS; ++i)
+        if (pthread_create(&threads[i], 0, increment_resource, 0) != 0 ||
+            pthread_create(&threads[i + NUM_THREADS],
+                           nullptr,
+                           decrement_resource,
+                           nullptr) != 0)
+            return 4;
+    for (int i = 0; i < NUM_THREADS * 2; ++i)
+        if (pthread_join(threads[i], 0) != 0)
+            return 5;
+    return (shared_resource == 0) ? 0 : 6;
+}
+
+int
+test_try_lock()
+{
+    ctl::mutex try_mtx;
+    if (!try_mtx.try_lock())
+        return 7;
+    if (try_mtx.try_lock())
+        return 8;
+    try_mtx.unlock();
+    return 0;
+}
+
+int
+main()
+{
+    int result;
+
+    result = test_basic_locking();
+    if (result != 0)
+        return result;
+
+    result = test_lock_contention();
+    if (result != 0)
+        return result;
+
+    result = test_try_lock();
+    if (result != 0)
+        return result;
+
+    CheckForMemoryLeaks();
+}
diff --git a/test/ctl/sort_test.cc b/test/ctl/sort_test.cc
new file mode 100644
index 000000000..2acc59917
--- /dev/null
+++ b/test/ctl/sort_test.cc
@@ -0,0 +1,130 @@
+// -*- mode:c++; indent-tabs-mode:nil; c-basic-offset:4; coding:utf-8 -*-
+// vi: set et ft=cpp ts=4 sts=4 sw=4 fenc=utf-8 :vi
+//
+// Copyright 2024 Justine Alexandra Roberts Tunney
+//
+// Permission to use, copy, modify, and/or distribute this software for
+// any purpose with or without fee is hereby granted, provided that the
+// above copyright notice and this permission notice appear in all copies.
+//
+// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL
+// WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED
+// WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE
+// AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
+// DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
+// PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
+// TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+// PERFORMANCE OF THIS SOFTWARE.
+
+#include "ctl/is_sorted.h"
+#include "ctl/sort.h"
+#include "ctl/string.h"
+#include "ctl/vector.h"
+#include "libc/mem/leaks.h"
+#include "libc/stdio/rand.h"
+
+// #include <algorithm>
+// #include <string>
+// #include <vector>
+// #define ctl std
+
+// Test sorting integers
+int
+test_sort_integers()
+{
+    ctl::vector<int> v = { 5, 2, 8, 1, 9, 3, 7, 6, 4 };
+    ctl::sort(v.begin(), v.end());
+    if (!ctl::is_sorted(v.begin(), v.end(), ctl::less<int>()))
+        return 1;
+    return 0;
+}
+
+// Test sorting with custom comparator
+int
+test_sort_custom_compare()
+{
+    ctl::vector<int> v = { 5, 2, 8, 1, 9, 3, 7, 6, 4 };
+    ctl::sort(v.begin(), v.end(), [](int a, int b) { return a > b; });
+    if (!ctl::is_sorted(v.begin(), v.end(), [](int a, int b) { return a > b; }))
+        return 2;
+    return 0;
+}
+
+// Test sorting strings
+int
+test_sort_strings()
+{
+    ctl::vector<ctl::string> v = { "banana", "apple", "cherry", "date" };
+    ctl::sort(v.begin(), v.end());
+    if (!ctl::is_sorted(v.begin(), v.end(), ctl::less<ctl::string>()))
+        return 3;
+    return 0;
+}
+
+// Test sorting with large number of elements
+int
+test_sort_large()
+{
+    const int SIZE = 10000;
+    ctl::vector<int> v(SIZE);
+    for (int i = 0; i < SIZE; ++i)
+        v[i] = rand() % SIZE;
+    ctl::sort(v.begin(), v.end());
+    if (!is_sorted(v.begin(), v.end(), ctl::less<int>()))
+        return 4;
+    return 0;
+}
+
+// Test sorting already sorted vector
+int
+test_sort_sorted()
+{
+    ctl::vector<int> v = { 1, 2, 3, 4, 5, 6, 7, 8, 9 };
+    ctl::sort(v.begin(), v.end());
+    if (!is_sorted(v.begin(), v.end(), ctl::less<int>()))
+        return 5;
+    return 0;
+}
+
+// Test sorting reverse sorted vector
+int
+test_sort_reverse()
+{
+    ctl::vector<int> v = { 9, 8, 7, 6, 5, 4, 3, 2, 1 };
+    ctl::sort(v.begin(), v.end());
+    if (!is_sorted(v.begin(), v.end(), ctl::less<int>()))
+        return 6;
+    return 0;
+}
+
+int
+main()
+{
+    int result;
+
+    result = test_sort_integers();
+    if (result != 0)
+        return result;
+
+    result = test_sort_custom_compare();
+    if (result != 0)
+        return result;
+
+    result = test_sort_strings();
+    if (result != 0)
+        return result;
+
+    result = test_sort_large();
+    if (result != 0)
+        return result;
+
+    result = test_sort_sorted();
+    if (result != 0)
+        return result;
+
+    result = test_sort_reverse();
+    if (result != 0)
+        return result;
+
+    CheckForMemoryLeaks();
+}
diff --git a/test/ctl/string_bench.cc b/test/ctl/string_bench.cc
index c59695dd1..b7b30c935 100644
--- a/test/ctl/string_bench.cc
+++ b/test/ctl/string_bench.cc
@@ -17,8 +17,8 @@
 // PERFORMANCE OF THIS SOFTWARE.
 
 #include "ctl/string.h"
-
-#include <__utility/move.h>
+#include "ctl/utility.h"
+#include "libc/mem/leaks.h"
 
 #include "libc/calls/struct/timespec.h"
 #include "libc/runtime/runtime.h"
@@ -100,7 +100,7 @@ main()
 
     BENCH(1000000, 1, {
         ctl::string s(small);
-        ctl::string s2(std::move(s));
+        ctl::string s2(ctl::move(s));
     });
 
     BENCH(1000000, 1, {
@@ -119,7 +119,7 @@ main()
 
     BENCH(1000000, 1, {
         ctl::string s(big);
-        ctl::string s2(std::move(s));
+        ctl::string s2(ctl::move(s));
     });
 
     BENCH(1000000, 1, {
@@ -142,5 +142,5 @@ main()
         BENCH(1000000, 1, { ctl::string s(big_trunc); });
     }
 
-    return 0;
+    CheckForMemoryLeaks();
 }
diff --git a/test/ctl/string_test.cc b/test/ctl/string_test.cc
index a3fd1f461..90b19e9c8 100644
--- a/test/ctl/string_test.cc
+++ b/test/ctl/string_test.cc
@@ -16,13 +16,14 @@
 // TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
 // PERFORMANCE OF THIS SOFTWARE.
 
+#include "ctl/is_same.h"
 #include "ctl/string.h"
-#include "ctl/type_traits.h"
 #include "libc/mem/leaks.h"
 
 #include "libc/str/str.h"
 
 // #include <string>
+// #include <utility>
 // #define ctl std
 
 using String = ctl::string;
diff --git a/test/ctl/string_view_test.cc b/test/ctl/string_view_test.cc
index 8ca1f8bee..a82743e15 100644
--- a/test/ctl/string_view_test.cc
+++ b/test/ctl/string_view_test.cc
@@ -173,5 +173,4 @@ main(int argc, char* argv[])
     }
 
     CheckForMemoryLeaks();
-    return 0;
 }
diff --git a/test/ctl/tuple_test.cc b/test/ctl/tuple_test.cc
new file mode 100644
index 000000000..0a3da6c6f
--- /dev/null
+++ b/test/ctl/tuple_test.cc
@@ -0,0 +1,161 @@
+// -*- mode:c++; indent-tabs-mode:nil; c-basic-offset:4; coding:utf-8 -*-
+// vi: set et ft=cpp ts=4 sts=4 sw=4 fenc=utf-8 :vi
+//
+// Copyright 2024 Justine Alexandra Roberts Tunney
+//
+// Permission to use, copy, modify, and/or distribute this software for
+// any purpose with or without fee is hereby granted, provided that the
+// above copyright notice and this permission notice appear in all copies.
+//
+// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL
+// WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED
+// WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE
+// AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
+// DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
+// PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
+// TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+// PERFORMANCE OF THIS SOFTWARE.
+
+#include "ctl/string.h"
+#include "ctl/tuple.h"
+#include "libc/mem/leaks.h"
+
+// #include <string>
+// #include <tuple>
+// #define ctl std
+
+int
+test_tuple_creation()
+{
+    ctl::tuple<int, double, ctl::string> t(1, 2.5, "hello");
+    if (ctl::get<0>(t) != 1 || ctl::get<1>(t) != 2.5 ||
+        ctl::get<2>(t) != "hello") {
+        return 1;
+    }
+    return 0;
+}
+
+int
+test_make_tuple()
+{
+    auto t = ctl::make_tuple(1, 2.5, ctl::string("hello"));
+    if (ctl::get<0>(t) != 1 || ctl::get<1>(t) != 2.5 ||
+        ctl::get<2>(t) != "hello") {
+        return 2;
+    }
+    return 0;
+}
+
+int
+test_tuple_get()
+{
+    ctl::tuple<int, double, ctl::string> t(1, 2.5, "hello");
+    if (ctl::get<0>(t) != 1)
+        return 3;
+    if (ctl::get<1>(t) != 2.5)
+        return 4;
+    if (ctl::get<2>(t) != "hello")
+        return 5;
+    return 0;
+}
+
+int
+test_tuple_comparison()
+{
+    auto t1 = ctl::make_tuple(1, 2.5, "hello");
+    auto t2 = ctl::make_tuple(1, 2.5, "hello");
+    auto t3 = ctl::make_tuple(2, 3.5, "world");
+
+    if (!(t1 == t2))
+        return 6;
+    if (t1 != t2)
+        return 7;
+    if (t1 == t3)
+        return 8;
+    if (!(t1 != t3))
+        return 9;
+
+    return 0;
+}
+
+int
+test_tuple_assignment()
+{
+    ctl::tuple<int, double, ctl::string> t1(1, 2.5, "hello");
+    ctl::tuple<int, double, ctl::string> t2;
+    t2 = t1;
+    if (!(t1 == t2))
+        return 10;
+    return 0;
+}
+
+int
+test_tuple_move()
+{
+    ctl::tuple<int, double, ctl::string> t1(1, 2.5, "hello");
+    ctl::tuple<int, double, ctl::string> t2(ctl::move(t1));
+    if (ctl::get<0>(t2) != 1 || ctl::get<1>(t2) != 2.5 ||
+        ctl::get<2>(t2) != "hello") {
+        return 11;
+    }
+    return 0;
+}
+
+int
+test_empty_tuple()
+{
+    ctl::tuple<> t;
+    ctl::tuple<> t2;
+    if (!(t == t2))
+        return 12;
+    return 0;
+}
+
+int
+test_single_element_tuple()
+{
+    ctl::tuple<int> t(42);
+    if (ctl::get<0>(t) != 42)
+        return 13;
+    return 0;
+}
+
+int
+main()
+{
+    int result;
+
+    result = test_tuple_creation();
+    if (result != 0)
+        return result;
+
+    result = test_make_tuple();
+    if (result != 0)
+        return result;
+
+    result = test_tuple_get();
+    if (result != 0)
+        return result;
+
+    result = test_tuple_comparison();
+    if (result != 0)
+        return result;
+
+    result = test_tuple_assignment();
+    if (result != 0)
+        return result;
+
+    result = test_tuple_move();
+    if (result != 0)
+        return result;
+
+    result = test_empty_tuple();
+    if (result != 0)
+        return result;
+
+    result = test_single_element_tuple();
+    if (result != 0)
+        return result;
+
+    CheckForMemoryLeaks();
+}
diff --git a/test/ctl/unique_ptr_test.cc b/test/ctl/unique_ptr_test.cc
index 87e4f30f2..75ed674ba 100644
--- a/test/ctl/unique_ptr_test.cc
+++ b/test/ctl/unique_ptr_test.cc
@@ -16,7 +16,7 @@
 // TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
 // PERFORMANCE OF THIS SOFTWARE.
 
-#include "ctl/type_traits.h"
+#include "ctl/is_same.h"
 #include "ctl/unique_ptr.h"
 #include "libc/mem/leaks.h"
 
@@ -41,29 +41,30 @@ MkRaw()
     return ctl::make_unique_for_overwrite<T>();
 }
 
-#undef ctl
+// #undef ctl
 
 static int g = 0;
 
 struct SetsGDeleter
 {
-    void operator()(auto*) const noexcept
+    void operator()(auto* x) const noexcept
     {
         ++g;
+        delete x;
     }
 };
 
 struct StatefulDeleter
 {
     char state;
-    void operator()(auto*) const noexcept
+    void operator()(auto* x) const noexcept
     {
     }
 };
 
 struct FinalDeleter final
 {
-    void operator()(auto*) const noexcept
+    void operator()(auto* x) const noexcept
     {
     }
 };
@@ -99,6 +100,7 @@ struct Derived : Base
 int
 main()
 {
+
     {
         Ptr<int> x(new int(5));
     }
@@ -186,9 +188,9 @@ main()
         g = 0;
         {
             auto x = Mk<SetsGDtor>();
-            x.release();
+            delete x.release();
         }
-        if (g)
+        if (g != 1)
             return 13;
     }
 
@@ -224,8 +226,5 @@ main()
         Ptr<Base> z(ctl::move(y));
     }
 
-    // next is 18
-
-    // TODO(mrdomino): Fix memory leaks reported by MODE=dbg
-    // CheckForMemoryLeaks();
+    CheckForMemoryLeaks();
 }