Im not understanding why we have 2 different options for `__m1/2` here.

[SergeyKopienko]

Im not understanding why we have 2 different options for __m1/2 here.
should it just be __m = __last1 - __left_bound_seq_1 + __last2 - __left_bound_seq_2? then we run intersection from the left bound to the last of each set?

Can any element between __first1/2 and __left_bound_seq_1/2 impact the intersection?

Originally posted by @danhoeflinger in #2320 (comment)