Regular omega-Languages with an Informative Right Congruence

Dana Angluin
(Yale University)
Dana Fisman
(Ben-Gurion University)

A regular language is almost fully characterized by its right congruence relation. Indeed, a regular language can always be recognized by a DFA isomorphic to the automaton corresponding to its right congruence, henceforth the Rightcon automaton. The same does not hold for regular omega-languages. The right congruence of a regular omega-language is not informative enough; many regular omega-languages have a trivial right congruence, and in general it is not always possible to define an omega-automaton recognizing a given language that is isomorphic to the rightcon automaton.

The class of weak regular omega-languages does have an informative right congruence. That is, any weak regular omega-language can always be recognized by a deterministic Büchi automaton that is isomorphic to the rightcon automaton. Weak regular omega-languages reside in the lower levels of the expressiveness hierarchy of regular omega-languages. Are there more expressive sub-classes of regular omega languages that have an informative right congruence? Can we fully characterize the class of languages with a trivial right congruence? In this paper we try to place some additional pieces of this big puzzle.

In Andrea Orlandini and Martin Zimmermann: Proceedings Ninth International Symposium on Games, Automata, Logics, and Formal Verification (GandALF 2018), Saarbrücken, Germany, 26-28th September 2018, Electronic Proceedings in Theoretical Computer Science 277, pp. 265–279.
Published: 7th September 2018.

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