Produces the elements of the two sets between greater_or_equal_to and
less_or_equal_to in order, noting whether each element appears in the left set,
the right set, or both. In the both case, both elements are returned, in case the
caller can distinguish between elements that are equal to the sets' comparator. Runs
in O(length t + length t').
type ('a, 'b) t = ('a, 'b) Sequence.Merge_with_duplicates_element.t = | Left of 'a |
| Right of 'b |
| Both of 'a * 'b |