1  template<typename _Tp, _Tp __v>
       2  struct integral_constant
       3  {
       4    static constexpr _Tp value = __v;
       5    typedef _Tp value_type;
       6    typedef integral_constant<_Tp, __v> type;
       7  };
       8  
       9  template<typename _Tp, _Tp __v>
      10  constexpr _Tp integral_constant<_Tp, __v>::value;
      11  
      12  typedef integral_constant<bool, false> false_type;
      13  
      14  
      15  template<typename _T1>
      16  struct Alien
      17  {
      18  };
      19  
      20  template<typename _T1>
      21  bool operator==(const Alien<_T1>& __x, const Alien<_T1>& __y);
      22  
      23  template<typename _Rep>
      24  struct duration;
      25  
      26  template<bool _DenIsOne>
      27  struct __duration_cast_impl
      28  {
      29  };
      30  
      31  template<typename _ToDur, typename _Rep>
      32  long Frob (const duration<_Rep>& __d)
      33  {
      34    typedef __duration_cast_impl<// finds ::operator==
      35  			       _ToDur::num == 1> __dc;
      36  
      37    return 0;
      38  }
      39  
      40  template<typename _Rep>
      41  struct duration
      42  {
      43  public:
      44    constexpr duration() = default;
      45  
      46    duration (const duration& __d)
      47    {
      48      Frob <duration> (__d);
      49    }
      50  };
      51  
      52  template<typename _Tp>
      53  struct __atomic_semaphore
      54  {
      55    template<typename _Rep>
      56    bool _M_try_acquire_for (const duration<_Rep>& __rtime) noexcept;
      57  
      58    void _M_release() noexcept;
      59  };
      60  
      61  template<long __least_max_value>
      62  class counting_semaphore
      63  {
      64    __atomic_semaphore<unsigned> _M_sem;
      65  
      66  public:
      67    explicit counting_semaphore() noexcept;
      68  
      69    void release() noexcept (noexcept (_M_sem._M_release ()));
      70  };
      71  
      72  class stop_token
      73  {
      74  public:
      75    counting_semaphore<1> _M_done;
      76  };
      77  
      78  bool operator==(const stop_token& __a, const stop_token& __b);