Quantifier Alternation in Two-Variable First-Order Logic with Successor Is Decidable

Authors Manfred Kufleitner, Alexander Lauser

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Manfred Kufleitner
Alexander Lauser

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Manfred Kufleitner and Alexander Lauser. Quantifier Alternation in Two-Variable First-Order Logic with Successor Is Decidable. In 30th International Symposium on Theoretical Aspects of Computer Science (STACS 2013). Leibniz International Proceedings in Informatics (LIPIcs), Volume 20, pp. 305-316, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2013)


We consider the quantifier alternation hierarchy within two-variable first-order logic FO^2[<,suc] over finite words with linear order and binary successor predicate. We give a single identity of omega-terms for each level of this hierarchy. This shows that for a given regular language and a non-negative integer~$m$ it is decidable whether the language is definable by a formula in FO^2[<,suc] which has at most m quantifier alternations. We also consider the alternation hierarchy of unary temporal logic TL[X,F,Y,P] defined by the maximal number of nested negations. This hierarchy coincides with the FO^2[<,suc] quantifier alternation hierarchy.
  • automata theory
  • semigroups
  • regular languages
  • first-order logic


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