constexpr month_weekday(const chrono::month& m, const chrono::weekday_indexed& wdi) noexcept;
constexpr chrono::month month() const noexcept;
constexpr chrono::weekday_indexed weekday_indexed() const noexcept;
constexpr bool ok() const noexcept;
constexpr bool operator==(const month_weekday& x, const month_weekday& y) noexcept;
template<class charT, class traits>
basic_ostream<charT, traits>&
operator<<(basic_ostream<charT, traits>& os, const month_weekday& mwd);