The two-variable guarded fragment with transitive guards is 2EXPTIME-hard

  • Authors:
  • Emanuel Kieronski

  • Affiliations:
  • Institute of Computer Science, University of Wrocłow, Wrocłow, Poland

  • Venue:
  • FOSSACS'03/ETAPS'03 Proceedings of the 6th International conference on Foundations of Software Science and Computation Structures and joint European conference on Theory and practice of software
  • Year:
  • 2003

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Abstract

We prove that the satisfiability problem for the two-variable guarded fragment with transitive guards GF2 +TG is 2EXPTIME-hard. This result closes the open questions left in [4], [17]. In fact, we show 2EXPTIME-hardness of minGF2 + TG, a fragment of GF2 + TG without equality and with just one transitive relation ???, which is the only non-unary symbol allowed. Our lower bound for minGF2 + TG matches the upper bound for the whole guarded fragment with transitive guards and the unrestricted number of variables GF + TG given by Szwast and Tendera [17], so in fact GF2 +TG is 2EXPTIME-complete. It is surprising that the complexity of minGF2 + TG is higher then the complexity of the variant with one-way transitive guards GF2 + ???TG [9]. The latter logic appears naturally as a counterpart of temporal logics without past operators.