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長谷部浩二＠筑波大学
--------------------------------------------- Date：14:00-15:00, Jan 23, 2012 Place: Room SB-911-1 (Laboratory of Advanced Research-B, 9th floor), Tsukuba-campus, University of Tsukuba http://www.tsukuba.ac.jp/english/access/tsukuba_access.html http://www.tsukuba.ac.jp/english/access/map_central.html
（筑波大学 筑波キャンパス，総合研究棟B，9階，911-1号室） http://www.tsukuba.ac.jp/access/tsukuba_access.html http://www.tsukuba.ac.jp/access/map_central.html
Speaker: Thomas Ågotnes, Department of Information Science and Media Studies, University of Bergen
Title: Group Announcement Logic
Abstract: Public announcement logic is used to reason about the epistemic pre- and post-conditions of actions in the form of public announcements. In the talk I will present Group Announcement Logic (GAL), an extension of public announcement logic with constructs (well known from coalition logic) of the form <G>phi, where G is a group of agents. In GAL, the meaning of <G>phi is that there exists an announcement that the members of G can jointly and truthfully make, and after that announcement is made public phi will be true. After introducing GAL I will discuss how it can be used to express properties such as "there is a sequence of truthful public announcements by agents in G, after which phi is true"; the distinction between "agent i knows *that* phi can be achieved by a public announcement" and "agent i knows *how* phi can be achieved by a public announcement"; and meta-logical properties such as axiomatization, expressivity and the complexity of the model checking problem. The talk is based on joint work with Philippe Balbiani, Hans van Ditmarsch and Pablo Seban. ---------------------------------------------