“…For instance, in automata theory, the theory of formal languages, and logics, it is used in connection with piecewise testable languages [66,67,45,46,47], or subword order and downward closures [39,52,51,71,7]. Naturally, subsequences appear in the area of combinatorics and algorithms on words [62,28,54,53,64,58,63,5,26], but they are also used for modelling concurrency [61,65,14], as well as in database theory (especially in connection with event stream processing [3,38,72]). Nevertheless, a series of classical, well-studied, and well-motivated combinatorial and algorithmic problems deal with subsequences.…”