constexpr explicit(see below) pair();
constexpr explicit(see below) pair(const T1& x, const T2& y);
template<class U1 = T1, class U2 = T2> constexpr explicit(see below) pair(U1&& x, U2&& y);
template<class U1, class U2> constexpr explicit(see below) pair(pair<U1, U2>& p);
template<class U1, class U2> constexpr explicit(see below) pair(const pair<U1, U2>& p);
template<class U1, class U2> constexpr explicit(see below) pair(pair<U1, U2>&& p);
template<class U1, class U2> constexpr explicit(see below) pair(const pair<U1, U2>&& p);
template<pair-like P> constexpr explicit(see below) pair(P&& p);
template<class... Args1, class... Args2>
constexpr pair(piecewise_construct_t,
tuple<Args1...> first_args, tuple<Args2...> second_args);
constexpr pair& operator=(const pair& p);
constexpr const pair& operator=(const pair& p) const;
template<class U1, class U2> constexpr pair& operator=(const pair<U1, U2>& p);
template<class U1, class U2> constexpr const pair& operator=(const pair<U1, U2>& p) const;
constexpr pair& operator=(pair&& p) noexcept(see below);
constexpr const pair& operator=(pair&& p) const;
template<class U1, class U2> constexpr pair& operator=(pair<U1, U2>&& p);
template<class U1, class U2> constexpr const pair& operator=(pair<U1, U2>&& p) const;
constexpr void swap(pair& p) noexcept(see below);
constexpr void swap(const pair& p) const noexcept(see below);
template<class T1, class T2, class U1, class U2>
constexpr bool operator==(const pair<T1, T2>& x, const pair<U1, U2>& y);
template<class T1, class T2, class U1, class U2>
constexpr common_comparison_category_t<synth-three-way-result<T1, U1>,
synth-three-way-result<T2, U2>>
operator<=>(const pair<T1, T2>& x, const pair<U1, U2>& y);
template<class T1, class T2>
constexpr void swap(pair<T1, T2>& x, pair<T1, T2>& y) noexcept(noexcept(x.swap(y)));
template<class T1, class T2>
constexpr void swap(const pair<T1, T2>& x, const pair<T1, T2>& y) noexcept(noexcept(x.swap(y)));
template<class T1, class T2>
constexpr pair<unwrap_ref_decay_t<T1>, unwrap_ref_decay_t<T2>> make_pair(T1&& x, T2&& y);
template<class T1, class T2>
struct tuple_size<pair<T1, T2>> : integral_constant<size_t, 2> { };
template<size_t I, class T1, class T2>
struct tuple_element<I, pair<T1, T2>> {
using type = see below ;
};
template<size_t I, class T1, class T2>
constexpr tuple_element_t<I, pair<T1, T2>>& get(pair<T1, T2>& p) noexcept;
template<size_t I, class T1, class T2>
constexpr const tuple_element_t<I, pair<T1, T2>>& get(const pair<T1, T2>& p) noexcept;
template<size_t I, class T1, class T2>
constexpr tuple_element_t<I, pair<T1, T2>>&& get(pair<T1, T2>&& p) noexcept;
template<size_t I, class T1, class T2>
constexpr const tuple_element_t<I, pair<T1, T2>>&& get(const pair<T1, T2>&& p) noexcept;
template<class T1, class T2>
constexpr T1& get(pair<T1, T2>& p) noexcept;
template<class T1, class T2>
constexpr const T1& get(const pair<T1, T2>& p) noexcept;
template<class T1, class T2>
constexpr T1&& get(pair<T1, T2>&& p) noexcept;
template<class T1, class T2>
constexpr const T1&& get(const pair<T1, T2>&& p) noexcept;
template<class T2, class T1>
constexpr T2& get(pair<T1, T2>& p) noexcept;
template<class T2, class T1>
constexpr const T2& get(const pair<T1, T2>& p) noexcept;
template<class T2, class T1>
constexpr T2&& get(pair<T1, T2>&& p) noexcept;
template<class T2, class T1>
constexpr const T2&& get(const pair<T1, T2>&& p) noexcept;
struct piecewise_construct_t {
explicit piecewise_construct_t() = default;
};
inline constexpr piecewise_construct_t piecewise_construct{};