template<class RandomAccessIterator>
  bool is_heap(RandomAccessIterator first, RandomAccessIterator last);
template<class ExecutionPolicy, class RandomAccessIterator>
  bool is_heap(ExecutionPolicy&& exec,
               RandomAccessIterator first, RandomAccessIterator last);
template<class RandomAccessIterator, class Compare>
  bool is_heap(RandomAccessIterator first, RandomAccessIterator last, Compare comp);
template<class ExecutionPolicy, class RandomAccessIterator, class Compare>
  bool is_heap(ExecutionPolicy&& exec,
               RandomAccessIterator first, RandomAccessIterator last, Compare comp);
template<class RandomAccessIterator>
  RandomAccessIterator is_heap_until(RandomAccessIterator first, RandomAccessIterator last);
template<class ExecutionPolicy, class RandomAccessIterator>
  RandomAccessIterator is_heap_until(ExecutionPolicy&& exec,
                                     RandomAccessIterator first, RandomAccessIterator last);
template<class RandomAccessIterator, class Compare>
  RandomAccessIterator is_heap_until(RandomAccessIterator first, RandomAccessIterator last,
                                     Compare comp);
template<class ExecutionPolicy, class RandomAccessIterator, class Compare>
  RandomAccessIterator is_heap_until(ExecutionPolicy&& exec,
                                     RandomAccessIterator first, RandomAccessIterator last,
                                     Compare comp);