template<class _RanIt,
	class _Diff> inline
	void _Sort(_RanIt _First, _RanIt _Last, _Diff _Ideal)
	{	// order [_First, _Last), using operator<
	_Diff _Count;
	for (; _ISORT_MAX < (_Count = _Last - _First) && 0 < _Ideal; )
		{	// divide and conquer by quicksort
		pair<_RanIt, _RanIt> _Mid = _Unguarded_partition(_First, _Last);
		_Ideal /= 2, _Ideal += _Ideal / 2;	// allow 1.5 log2(N) divisions

		if (_Mid.first - _First < _Last - _Mid.second)	// loop on larger half
			_Sort(_First, _Mid.first, _Ideal), _First = _Mid.second;
		else
			_Sort(_Mid.second, _Last, _Ideal), _Last = _Mid.first;
		}

	if (_ISORT_MAX < _Count)
		{	// heap sort if too many divisions
		std::make_heap(_First, _Last);
		std::sort_heap(_First, _Last);
		}
	else if (1 < _Count)
		_Insertion_sort(_First, _Last);	// small, insertion sort
	}