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New Techniques for Universality in Unambiguous Register Automata

Authors Wojciech Czerwiński , Antoine Mottet , Karin Quaas



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Author Details

Wojciech Czerwiński
  • University of Warsaw, Poland
Antoine Mottet
  • Department of Algebra, Faculty of Mathematics and Physics, Charles University, Prague, Czech Republic
Karin Quaas
  • University of Leipzig, Germany

Acknowledgements

We thank Lorenzo Clemente, Sławomir Lasota, and Radosław Piórkowski for inspiring discussions on URA.

Cite AsGet BibTex

Wojciech Czerwiński, Antoine Mottet, and Karin Quaas. New Techniques for Universality in Unambiguous Register Automata. In 48th International Colloquium on Automata, Languages, and Programming (ICALP 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 198, pp. 129:1-129:16, Schloss Dagstuhl - Leibniz-Zentrum für Informatik (2021)
https://doi.org/10.4230/LIPIcs.ICALP.2021.129

Abstract

Register automata are finite automata equipped with a finite set of registers ranging over the domain of some relational structure like (ℕ; =) or (ℚ; <). Register automata process words over the domain, and along a run of the automaton, the registers can store data from the input word for later comparisons. It is long known that the universality problem, i.e., the problem to decide whether a given register automaton accepts all words over the domain, is undecidable. Recently, we proved the problem to be decidable in 2-ExpSpace if the register automaton under study is over (ℕ; =) and unambiguous, i.e., every input word has at most one accepting run; this result was shortly after improved to 2-ExpTime by Barloy and Clemente. In this paper, we go one step further and prove that the problem is in ExpSpace, and in PSpace if the number of registers is fixed. Our proof is based on new techniques that additionally allow us to show that the problem is in PSpace for single-register automata over (ℚ; <). As a third technical contribution we prove that the problem is decidable (in ExpSpace) for a more expressive model of unambiguous register automata, where the registers can take values nondeterministically, if defined over (ℕ; =) and only one register is used.

Subject Classification

ACM Subject Classification
  • Theory of computation → Automata over infinite objects
Keywords
  • Register Automata
  • Data Languages
  • Unambiguity
  • Unambiguous
  • Universality
  • Containment
  • Language Inclusion
  • Equivalence

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