Thomas Ågotnes, "Playing Games with Dynamic Epistemic Logic"

Dynamic epistemic logic describes the possible information-changing actions available to individual agents, and their knowledge pre- and post conditions. For example, public announcement logic describes actions in the form of public, truthful announcements. However, little research so far has considered describing and analysing rational choice between such actions, i.e., predicting what rational self-interested agents actually will or should do. Since the outcome of information exchange ultimately depends on the actions chosen by all the agents in the system, and assuming that agents have preferences over such outcomes, i.e., over multi-agent epistemic states, this is a game theoretic scenario. This is an interesting general research direction, combining logic and game theory in the study of rational information exchange. In the talk I will focus on one particular setting: the case where available actions are public announcements, and where each agent has a (typically epistemic) goal formula that she would like to become true. What will each agent announce? The truth of the goal formula also depends on the announcements made by other agents, thus we have a game-theoretic scenario. I discuss how such *public announcement games* can be analysed. I will also briefly discuss two other settings. First, consider coalition formation: if agents are allowed to form coalitions, which coalitions will form, i.e., which are coalitions are stable? We can answer such questions by studying the *coalitional* public announcement games inherent in Kripke models. Second, consider the setting where instead of choosing an announcement each player chooses a question the other player is obliged to truthfully answer. What are the best questions to ask? Again, this question can be discussed by analysing the resulting *question-answer games*. The talk is based on joint work with Hans van Ditmarsch, and parts also with Johan van Benthem and Stefan Minica.