A Note on Bisimulation and Modal Equivalence in Provability Logic and Interpretability Logic

  • Authors:
  • Vedran Čačić;Domagoj Vrgoč

  • Affiliations:
  • Department of Mathematics, University of Zagreb, Zagreb, Croatia;School of Informatics, University of Edinburgh, Edinburgh, Scotland, UK and Faculty of Agriculture, University of Zagreb, Zagreb, Croatia

  • Venue:
  • Studia Logica
  • Year:
  • 2013

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Abstract

Provability logic is a modal logic for studying properties of provability predicates, and Interpretability logic for studying interpretability between logical theories. Their natural models are GL-models and Veltman models, for which the accessibility relation is well-founded. That's why the usual counterexample showing the necessity of finite image property in Hennessy-Milner theorem (see [1]) doesn't exist for them. However, we show that the analogous condition must still hold, by constructing two GL-models with worlds in them that are modally equivalent but not bisimilar, and showing how these GL-models can be converted to Veltman models with the same properties. In the process we develop some useful constructions: games on Veltman models, chains, and general method of transformation from GL-models/frames to Veltman ones.