std::set_intersection weeken precondition

[NiceAndPeter]

The std::set_intersection algorithm forbids overlap of the input ranges with the output range, but if first2 and result would be equal, the algorithm could still work.
This would allow inplace execution without memory allocation, which is a big plus.

26.8.7.4 set_intersection (wording)

replace: The resulting range does not overlap with either of the original ranges.
with: result may be equal first2, otherwise the resulting range does not overlap with either of the original ranges.

[jensmaurer]

Changing preconditions of an algorithm is not an editorial matter. Please submit an LWG issue, as described here: https://isocpp.org/std/submit-issue

[NiceAndPeter]

Thank you. I did not know that.