There are 6 ways of arranging the letters A, B and C: ABC, ACB, BAC, BCA, CAB, and CBA. The string "ABCABACBA" contains each of these as a substring, and would therefore be sorted left.

Sequence contains each possible way its distinct elements can be arranged as a subsequence vs. not so.

https://en.wikipedia.org/wiki/Superpermutation

Leo Crabbe