User blog comment:Syst3ms/A formal interpretation of Y sequence : F sequence/@comment-35470197-20190810061448/@comment-35392788-20190810131337

The difference sequence would be (1,2,1,2). We always try to find a smaller number to subtract when constructing the difference sequence. However, in such a case, elements have to be skipped. O_{a,b}, the "offset sequence", accounts for this.

In the case of (1,2,4,2,4), the offset sequence would be (1,1,3,1). The offset sequence makes sure that two sequences with the same difference sequence get expanded differently.

The sequence (1,2,4,5,4) also has difference sequence (1,2,1,2), but its offset sequence is (1,1,1,3)