Topological Perspective on the Hybrid Proof Rules

  • Authors:
  • Balder ten Cate;Tadeusz Litak

  • Affiliations:
  • ISLA -- Informatics Institute, Universiteit van Amsterdam, Amsterdam, The Netherlands;School of Information Science, JAIST, Asahidai 1-1, Nomi-shi, Ishikawa, 923-1292 Japan

  • Venue:
  • Electronic Notes in Theoretical Computer Science (ENTCS)
  • Year:
  • 2007

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Abstract

We consider the non-orthodox proof rules of hybrid logic from the viewpoint of topological semantics. Topological semantics is more general than Kripke semantics. We show that the hybrid proof rule BG is topologically not sound. Indeed, among all topological spaces the BG rule characterizes those that can be represented as a Kripke frame (i.e., the Alexandroff spaces). We also demonstrate that, when the BG rule is dropped and only the Name rule is kept, one can prove a general topological completeness result for hybrid logics axiomatized by pure formulas. Finally, we indicate some limitations of the topological expressive power of pure formulas. All results generalize to neighborhood frames.