Decomposable graphs and definitions with no quantifier alternation

  • Authors:
  • Oleg Pikhurko;Joel Spencer;Oleg Verbitsky

  • Affiliations:
  • Department of Mathematical Sciences, Carnegie Mellon University, Pittsburgh, PA 15213, USA;Courant Institute, New York University, New York, NY 10012, USA;Institut für Informatik, Humboldt Universität Berlin, D-10099 Berlin, Germany

  • Venue:
  • European Journal of Combinatorics
  • Year:
  • 2007

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Abstract

Let D(G) be the minimum quantifier depth of a first order sentence @F that defines a graph G up to isomorphism. Let D"0(G) be the version of D(G) where we do not allow quantifier alternations in @F. Define q"0(n) to be the minimum of D"0(G) over all graphs G of order n. We prove that for all n we have log^*n-log^*log^*n-2@?q"0(n)@?log^*n+22, where log^*n is equal to the minimum number of iterations of the binary logarithm needed to bring n to 1 or below. The upper bound is obtained by constructing special graphs with modular decomposition of very small depth.