Regular ω-Languages with an informative right congruence

Dana Angluin, Dana Fisman

Research output: Contribution to journalConference articlepeer-review

6 Scopus citations


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 ω-languages. The right congruence of a regular ω-language is not informative enough; many regular ω-languages have a trivial right congruence, and in general it is not always possible to define an ω-automaton recognizing a given language that is isomorphic to the rightcon automaton. The class of weak regular ω-languages does have an informative right congruence. That is, any weak regular ω-language can always be recognized by a deterministic Büchi automaton that is isomorphic to the rightcon automaton. Weak regular ω-languages reside in the lower levels of the expressiveness hierarchy of regular ω-languages. Are there more expressive sub-classes of regular ω-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.

Original languageEnglish
Pages (from-to)265-279
Number of pages15
JournalElectronic Proceedings in Theoretical Computer Science, EPTCS
StatePublished - 7 Sep 2018
Event9th International Symposium on Games, Automata, Logics, and Formal Verification, G and ALF 2018 - Saarbrucken, Germany
Duration: 26 Sep 201828 Sep 2018

ASJC Scopus subject areas

  • Software


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