SI-8695  SeqLike has unintuitive implementation of combinations

Clarified what `combinations` means in the docs.
typo on `qu`.  You don't have a keyboard macro for `sequence` and `iterator` by now?

I think a paragraph break would give us a nice break after this sentence, too.

I guess two subsequences are identical if their elements compare equal using equals?

It would be pretty cool if you pronounced "subsequence" with the same stress as "consequence."  Cool in an arcane way.