constexpr explicit weekday_last(const chrono::weekday& wd) noexcept;
constexpr chrono::weekday weekday() const noexcept;
constexpr bool ok() const noexcept;
constexpr bool operator==(const weekday_last& x, const weekday_last& y) noexcept;
template<class charT, class traits>
basic_ostream<charT, traits>&
operator<<(basic_ostream<charT, traits>& os, const weekday_last& wdl);