13 April 2021, The Utrecht Logic in Progress Series (TULIPS), Helle Hvid Hansen

Abstract: Game logic was introduced by Rohit Parikh in the 1980s as a generalisation of propositional dynamic logic (PDL) for reasoning about outcomes that players can force in determined 2-player games. Semantically, the generalisation from programs to games is mirrored by moving from Kripke models to monotone neighbourhood models. Parikh proposed a natural PDL-style Hilbert system which was easily proved to be sound, but its completeness remained an open problem.
In our LISC 2019 paper, we introduce a cut-free sequent calculus for game logic, and two cut-free sequent calculi that manipulate annotated formulas, one for game logic and one for the monotone μ-calculus, the variant of the polymodal μ-calculus where the semantics is given by monotone neighbourhood models instead of Kripke structures. We show these systems are sound and complete, and that completeness of Parikh’s axiomatization follows. Our approach builds on ideas and results by Afshari & Leigh (LICS 2017) in that we obtain completeness via a sequence of proof transformations between the systems. A crucial ingredient is a validity-preserving translation from game logic to the monotone μ-calculus.
This is joint work with Sebastian Enqvist, Johannes Marti, Clemens Kupke and Yde Venema.

Please contact the organizer Colin R. Caret at c.r.caret at uu.nl if you would like to join the online meeting.