Kleene Theorems for Lasso Languages and $\omega$-Languages

Abstract

Automata operating on pairs of words were introduced as an alternative way of capturing acceptance of regular $\omega$-languages. Families of DFAs and lasso automata operating on such pairs followed, giving rise to minimisation algorithms, a Myhill-Nerode theorem and language learning algorithms. Yet Kleene theorems for such a well-established class are still missing. We introduce rational lasso languages and expressions, show a Kleene theorem for lasso languages and explore the connection between rational lasso and $\omega$-expressions, which yields a Kleene theorem for $\omega$-languages with respect to saturated lasso automata. For one direction of the Kleene theorems, we also provide a Brzozowski construction for lasso automata from rational lasso expressions.