BTL2 and the expressive power of ECTL+

  • Authors:
  • Alexander Rabinovich;Philippe Schnoebelen

  • Affiliations:
  • Department of Computer Science, Tel Aviv University, Ramat Aviv, Tel Aviv, Israel;Lab. Spécification et Vérification (LSV), ENS de Cachan and CNRS, France

  • Venue:
  • Information and Computation
  • Year:
  • 2006

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Abstract

We show that ECTL+, the classical extension of CTL with fairness properties, is expressively equivalent to BTL2, a natural fragment of the monadic logic of order. BTL2 is the branching-time logic with arbitrary quantification over paths, and where path formulac are restricted to quantifier depth 2 first-order formulae in the monadic logic of order. This result, linking ECTL+ to a natural fragment of the monadic logic of order, provides a characterization that other branching-time logics, e.g., CTL, lack. We then go on to show that ECTL+ and BTL2 are not finitely based (i.e., they cannot be defined by a finite set of temporal modalities) and that their model-checking problems are of the same complexity.