Coalgebraic Epistemic Update Without Change of Model

  • Corina Cîrstea
  • Mehrnoosh Sadrzadeh
Part of the Lecture Notes in Computer Science book series (LNCS, volume 4624)


We present a coalgebraic semantics for reasoning about information update in multi-agent systems. The novelty is that we have one structure for both states and actions and thus our models do not involve the ”change-of-model” phenomena that arise when using Kripke models. However, we prove that the usual models can be constructed from ours by categorical adjunction. The generality and abstraction of our coalgebraic model turns out to be extremely useful in proving preservation properties of update. In particular, we prove that positive knowledge is preserved and acquired as a result of epistemic update. We also prove common and nested knowledge properties of epistemic updates induced by specific epistemic actions such as public and private announcements, lying, and in particular unsafe actions of security protocols. Our model directly gives rise to a coalgebraic logic with both dynamic and epistemic modalities. We prove a soundness and completeness result for this logic, and illustrate the applicability of the logic by deriving knowledge properties of a simple security protocol.


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Copyright information

© Springer-Verlag Berlin Heidelberg 2007

Authors and Affiliations

  • Corina Cîrstea
    • 1
  • Mehrnoosh Sadrzadeh
    • 1
  1. 1.School of Electronics and Computer Science, University of Southampton 

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