std::chrono::operator==,<,<=,>,>=,<=>(std::chrono::leap_second)
|   在标头  <chrono> 定义
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|   constexpr bool operator==( const std::chrono::leap_second& x, const std::chrono::leap_second& y ) noexcept;  | 
(1) | (C++20 起) | 
|   constexpr std::strong_ordering operator<=>( const std::chrono::leap_second& x, const std::chrono::leap_second& y ) noexcept;  | 
(2) | (C++20 起) | 
|   template< class Duration >  constexpr bool operator==( const std::chrono::leap_second& x,   | 
(3) | (C++20 起) | 
|   template< class Duration >  constexpr bool operator< ( const std::chrono::leap_second& x,   | 
(4) | (C++20 起) | 
|   template< class Duration >  constexpr bool operator< ( const std::chrono::sys_time<Duration>& x,   | 
(5) | (C++20 起) | 
|   template< class Duration >  constexpr bool operator> ( const std::chrono::leap_second& x,   | 
(6) | (C++20 起) | 
|   template< class Duration >  constexpr bool operator> ( const std::chrono::sys_time<Duration>& x,   | 
(7) | (C++20 起) | 
|   template< class Duration >  constexpr bool operator<=( const std::chrono::leap_second& x,   | 
(8) | (C++20 起) | 
|   template< class Duration >  constexpr bool operator<=( const std::chrono::sys_time<Duration>& x,   | 
(9) | (C++20 起) | 
|   template< class Duration >  constexpr bool operator>=( const std::chrono::leap& x,   | 
(10) | (C++20 起) | 
|   template< class Duration >  constexpr bool operator>=( const std::chrono::sys_time<Duration>& x,   | 
(11) | (C++20 起) | 
|   template< class Duration >     requires std::three_way_comparable_with<  | 
(12) | (C++20 起) | 
比较对象 x 与 y 所表示的日期和时间。
(12) 的返回类型从 x.date() <=> y 推导,从而为 std::chrono::seconds 与 Duration 的三路比较结果类型。
!= 运算符从 == 运算符合成。