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09:00  Ludics and interactive completeness SPEAKER: Kazushige Terui 
09:45  Forward and backward induction in dynamic games: Distilling the axiomatic differences on common ground SPEAKER: Sujata Ghosh ABSTRACT. Backward Induction (BI) is the basic solution concept for finite games with perfect information. It is the procedure to find out all the subgameperfect equilibria in such games, i.e. the Nash equilibria in which incredible threats are precluded. An alternative approach to solving games with perfect information is to employ Forward Induction (FI), with which players do assess their opponents’ future behavior on the basis of these opponents’ past moves. A prominent solution concept embodying FI is ExtensiveForm Rationalizability (EFR), in which the active player at each node reacts optimally to a best rationalization of her opponents’ past behavior. Both BI and EFR are, strictly speaking, distinct iterative heuristics of strategy sieving, whose technical definitions do not directly disclose their epistemic motivation. This calls for exposing the different axiomatic assumptions underlying the two solution concepts, in a way that will enable an explicit comparison between them. This (ongoing) work aims at setting up an appropriate epistemic logic syntax, and at formulating directly comparable axiom systems characterizing BI and EFR. 
10:45  Signaling in independencefriendly logic SPEAKER: Gabriel Sandu 
11:30  Game Reductions SPEAKER: Dietmar Berwanger ABSTRACT. One recurring pattern in strategic reasoning consists in constructing a strategy for one game while playing another, auxiliary game on the side. EhrenfeuchtFraisse games can be seen as an instance of this technique. Although close to the concept of reduction in computation, transferring strategies between games is typically used as a proof artifice, without explicit formalisation. In this talk, we set out with a construction that underlies recent results about infinite games with imperfect monitoring. On basis of this, we illustrate more general features of a strategy transfer mechanism and outline a formal approach via metagames.

12:00  Game Semantics from a Cognitive Modeling Standpoint SPEAKER: unknown ABSTRACT. Wittgenstein has suggested an analogy between having a proof and winning a game. Two research programs that have undertaken to make this analogy formally precise: gametheoretic semantics (GTS) and dialogical logic (DL) but have so come up only with a partial reduction of logic to language games. Specifically, they have failed to specify preferences for the players, and inference mechanisms by which dominated strategies are eliminated, and by which strategic profiles that realize proofs are selected. Instead, they introduce ad hoc restrictions on strategies by means of game rules that guarantee the games to realize modelchecking (GTS) and proofs (DL) procedures. We show how these restrictions can be derived from preference profiles of boundedrational players, and specify inference mechanisms for strategy selection, based on some assumptions that select the player types. Our model does not answer a foundational agenda but should be viewed as an exercise in cognitive modeling, which bridges the watershed between formal and cognitive semantics, and may yield some insights into how logical reasoning could have emerged from natural language argumentation. 
12:30  Emulating Diffusion and Best Response Dynamics in Social Networks using Action Models SPEAKER: Rasmus K. Rendsvig ABSTRACT. Threshold models and their dynamics may be used to model the spread of behaviors, fashions or language use in social networks. Regarding such as Kripke models, it is shown how standard update mechanisms may be emulated using action models. The suitable class of action models is specified and shown to include models charaterizing best response dynamics of both coordination and anticoordination games played on graphs. Hereby, new links between social network theory, game theory and dynamic ‘epistemic’ logic are drawn. 
14:30  Semantic games for Łukasiewicz logic SPEAKER: Ondrej Majer 
15:15  Game Semantics for Conditional Logic SPEAKER: Johannes Marti ABSTRACT. In this talk we introduce a game semantics for conditional logic. We 
15:45  MultiAgent Dialogical Games for Modal Logic SPEAKER: Martin Sticht ABSTRACT. Dialogical Logic as a gametheoretic approach was introduced by Lorenzen and Lorenz and can be used to check validity of formulae for different kinds of logics. The system has been extended by Rahman and Rückert to cope with modal logic. Dialogues are very flexible as one can simply exchange their underlying rules to obtain decision procedures for other kinds of logic. A problem that occurs with the dialogues is that the amount of possible moves the players can perform in the game often cause a very high branching which makes the implementation inefficient when one wants to show or refute validity of formulae. We modify the system by introducing further players who all try to show validity of a formula together. This new approach works in a more deterministic way and thereby provides a plan to parallelize the reasoning process. 
16:30  Noncharacterizability in belief revision: an application of finite model theory SPEAKER: Jon Yaggie ABSTRACT. A formal framework is given for the characterizability of a class of belief revision operators, defined using minimization over a class of partial preorders, by postulates. It is shown that for partial orders characterizability implies a definability property of the class of partial orders in monadic secondorder logic. Based on a nondefinability result for a class of partial orders, an example is given of a noncharacterizable class of revision operators. This appears to be the first noncharacterizability result in belief revision. 
17:00  Game Semantics for Some NonClassical Logics SPEAKER: Can Baskent ABSTRACT. Our main goal in this paper is to give game semantics for various nonclassical logics, and observe how nonclassical logical elements change the verification game. 
19:00  VSL Public Lecture: Gödel in Vienna SPEAKER: Karl Sigmund 