        larger than the start offset but smaller than the end offset. This means for a zero length span
        Span(x,x), the number x is contained in the span, but no other number &gt; x.

        Two spans overlap, if there is at least one integer that is included in both number sets. So
        Span(1,1) overlaps with Span(1,1) because the integer 1 is in both number sets. Span(1,1) overlaps
        with Span(1,2) but not with Span(2,2) or Span(2,3).   Span(1,1) also does not overlap with Span(0,1).


 