On shuffle products, acyclic automata and piecewise-testable languages
Résumé
We show that the shuffle $L\unicode{x29E2} F$ of a piecewise-testable language $L$ and a finite language $F$ is piecewise-testable. The proof relies on a classic but little-used automata-theoretic characterization of piecewise-testable languages. We also discuss some mild generalizations of the main result, and provide bounds on the piecewise complexity of $L\unicode{x29E2} F$."