The Bounded Weak Monadic Quantifier Alternation Hierarchy of Equational Graphs Is Infinite

  • Authors:
  • Olivier Ly

  • Affiliations:
  • -

  • Venue:
  • FST TCS 2000 Proceedings of the 20th Conference on Foundations of Software Technology and Theoretical Computer Science
  • Year:
  • 2000

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Abstract

Here we deal with the question of definability of infinite graphs up to isomorphism by weak monadic second-order formulæ. In this respect, we prove that the quantifier alternation bounded hierarchy of equational graphs is infinite. Two proofs are given: the first one is based on the Ehrenfeucht-FraissÉ games; the second one uses the arithmetical hierarchy. Next, we give a new proof of the Thomas's result according to which the bounded hierarchy of the weak monadic second-order logic of the complete binary tree is infinite.