friend constexpr bool operator==(reference_wrapper x, reference_wrapper y);
friend constexpr bool operator==(reference_wrapper x, const T& y);
friend constexpr bool operator==(reference_wrapper x, reference_wrapper<const T> y);
friend constexpr auto operator<=>(reference_wrapper x, reference_wrapper y);
friend constexpr auto operator<=>(reference_wrapper x, const T& y);
friend constexpr auto operator<=>(reference_wrapper x, reference_wrapper<const T> y);