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// mostly freestanding
#include <compare>
#include <initializer_list>
 
namespace std {
 // class template array
 template<class T, size_t N>
 struct array; // partially freestanding
 
 template<class T, size_t N>
 constexpr bool operator==(const array<T, N>& x, const array<T, N>& y);
 template<class T, size_t N>
 constexpr /*synth-three-way-result*/<T> operator<=>(const array<T, N>& x,
 const array<T, N>& y);
 
 // specialized algorithms
 template<class T, size_t N>
 constexpr void swap(array<T, N>& x, array<T, N>& y) noexcept(noexcept(x.swap(y)));
 
 // array creation functions
 template<class T, size_t N>
 constexpr array<remove_cv_t<T>, N> to_array(T (&a)[N]);
 template<class T, size_t N>
 constexpr array<remove_cv_t<T>, N> to_array(T (&&a)[N]);
 
 // tuple interface
 template<class T>
 struct tuple_size;
 template<size_t I, class T>
 struct tuple_element;
 template<class T, size_t N>
 struct tuple_size<array<T, N>>;
 template<size_t I, class T, size_t N>
 struct tuple_element<I, array<T, N>>;
 template<size_t I, class T, size_t N>
 constexpr T& get(array<T, N>&) noexcept;
 template<size_t I, class T, size_t N>
 constexpr T&& get(array<T, N>&&) noexcept;
 template<size_t I, class T, size_t N>
 constexpr const T& get(const array<T, N>&) noexcept;
 template<size_t I, class T, size_t N>
 constexpr const T&& get(const array<T, N>&&) noexcept;
}

namespace std {
 template<class T, size_t N>
 struct array
 {
 // types
 using value_type = T;
 using pointer = T*;
 using const_pointer = const T*;
 using reference = T&;
 using const_reference = const T&;
 using size_type = size_t;
 using difference_type = ptrdiff_t;
 using iterator = /* implementation-defined */;
 using const_iterator = /* implementation-defined */;
 using reverse_iterator = std::reverse_iterator <iterator>;
 using const_reverse_iterator = std::reverse_iterator <const_iterator>;
 
 // no explicit construct/copy/destroy for aggregate type
 
 constexpr void fill(const T& u);
 constexpr void swap(array&) noexcept(is_nothrow_swappable_v<T>);
 
 // iterators
 constexpr iterator begin() noexcept;
 constexpr const_iterator begin() const noexcept;
 constexpr iterator end() noexcept;
 constexpr const_iterator end() const noexcept;
 
 constexpr reverse_iterator rbegin() noexcept;
 constexpr const_reverse_iterator rbegin() const noexcept;
 constexpr reverse_iterator rend() noexcept;
 constexpr const_reverse_iterator rend() const noexcept;
 
 constexpr const_iterator cbegin() const noexcept;
 constexpr const_iterator cend() const noexcept;
 constexpr const_reverse_iterator crbegin() const noexcept;
 constexpr const_reverse_iterator crend() const noexcept;
 
 // capacity
 constexpr bool empty() const noexcept;
 constexpr size_type size() const noexcept;
 constexpr size_type max_size() const noexcept;
 
 // element access
 constexpr reference operator[](size_type n);
 constexpr const_reference operator[](size_type n) const;
 constexpr reference at(size_type n); // freestanding-deleted
 constexpr const_reference at(size_type n) const; // freestanding-deleted
 constexpr reference front();
 constexpr const_reference front() const;
 constexpr reference back();
 constexpr const_reference back() const;
 
 constexpr T* data() noexcept;
 constexpr const T* data() const noexcept;
 };
 
 template<class T, class... U>
 array(T, U...) -> array<T, 1 + sizeof...(U)>;
}