Modal Logic and the Two-Variable Fragment

  • Authors:
  • Carsten Lutz;Ulrike Sattler;Frank Wolter

  • Affiliations:
  • -;-;-

  • Venue:
  • CSL '01 Proceedings of the 15th International Workshop on Computer Science Logic
  • Year:
  • 2001

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Abstract

We introduce a modal language L which is obtained from standard modal logic by adding the difference operator and modal operators interpreted by boolean combinations and the converse of accessibility relations. It is proved that L has the same expressive power as the two-variable fragment FO2 of first-order logic but speaks less succinctly about relational structures: if the number of relations is bounded, then L- satisfiability is EXPTIME-complete but FO2 satisfiability is NEXPTIME-complete. We indicate that the relation between L and FO2 provides a general framework for comparing modal and temporal languages with first-order languages.