Invited Speakers

ABSTRACT: This talk is based on joint work with Sonja Smets. I investigate the relation between probabilistic and qualitative (relational) models for belief revision, and between the corresponding updates. I use the Popper-Renyi theory of conditional probability, introducing discrete conditional probabilistic models for (conditional) belief, and comparing them with the more standard plausibility models. I also consider a related notion, that of "safe belief", which is a weak (non-negatively introspective) type of "knowledge". I present a probabilistic version of this concept ("degree of safety") and analyze its role in games. I develop a theory of probabilistic dynamic belief revision, introducing probabilistic action models for doxastic events (such as various forms of learning and communication) and a notion of probabilistic update product, which incorporates a belief revision mechanism. I finish with the reduction laws that completely axiomatize the qualitative logic of doxastic events, and with some open problems concerning the corresponding probabilistic logic.

BIOGRAPHY:
-1989: Masters of Science. University of Bucharest (Department of Mathematics), Bucharest, Romania.
-1993-1998: Fulbright scholar, at Indiana University (Bloomington, Indiana, USA).
-1998: Ph.D. in Mathematics from Indiana University, under the supervision of Jon Barwise. Title of thesis: "STS: A Structural Theory of Sets".
-1998-2001: Post-doctoral researcher at CWI (Amsterdam), in the group of Jan Rutten, and at ILLC (University of Amsterdam), in the group of J. van Benthem and Y. Venema.
-2001-present: University Lecturer at the Oxford University Computing Laboratory, in the group of S. Abramsky.

ABSTRACT: Recent developments in the interface of Economics and Logic yield the promise of capturing phenomena in strategic interaction that was previously beyond theoretical economic modelling. We consider one such application in the case of strategic situations that players may perceive differently. We show that the content of messages sent in this setting carries strategic implications without resorting to prior conventions and beyond the observations made in the literature dealing with cheap talk communications. The content of the message becomes strategically meaningful since it reveals perceptions. Various forms of interaction between meaningful statements and strategic behavior are discussed.

BIOGRAPHY: Yossi Feinberg is an associate professor of economics at the Graduate School of Business at Stanford University. He received his PhD in Mathematics from the Hebrew University in Jerusalem in 1997 under the supervision of Nobel Laureate Robert Aumann. Yossi works mainly in the field of foundations of economic theory. His recent work includes the introduction of games with unawareness and analysis of strategic decision making in the face of unawareness, other recent work concerns with the testing of stochastic predictions in a non-Bayesian, non-parametric, setting. Yossi is an associate editor of the Journal of Economic Theory.

BIOGRAPHY: Vincent F. Hendricks is Professor of Formal Philosophy at Roskilde University in Denmark and member of IIP, the Institut Internationale de Philosophie. His work concentrates primarily on bringing mainstream and formal approaches to epistemology together through modal operator theory. Modal operator theory is the cocktail obtained by mixing alethic, tense and epistemic logic with elements from formal learning theory in order to study the limiting validity of convergent knowledge. This paradigm has been articulated in a number papers and books notably The Convergence of Scientific Knowledge (Springer 2001) and Mainstream and Formal Epistemology (Cambrdige University Press 2006). Vincent F. Hendricks is editor-in-chief of Synthese, Synthese Library and founder of OLOG - The Network for Philosophical Logic and Its Applications [1] and chief editor of ONEWS - The Newsletter for Philosophical Logic and Its Applications.

ABSTRACT: As two case studies in utilising modal logic for social software, we present two modal logics, the first being Modal Coalition Game Logic, in which we can reason about coalitional games, in the sense of cooperative game theory. Other than for instance Pauly's Coalition Logic, we can directly refer to agents' preferences. Moreover, we interpret our language directly on coalitional games as defined in Osborne and Rubinstein. In this logic, we can express notions like the core and imputations. Our second logic is designed to reason about Judgment and Preference aggregation. In particular, we present an axiomatisation in which Arrows' theorem is derivable. We will demonstrate that from a modal logic point of view, completeness of both logics can be obtained by adding some 'extended modal power' to the language: in the case of Coalition Games, we add nominals for agenda-items to the language, and in the case of the Social Welfare Logic, the modal D-operator comes to the rescue.

BIOGRAPHY: Wiebe van der Hoek is currently head of the Agent ART Group (University of Liverpool) whose research in agents concentrates on Logics for Agent Systems, Cooperation, Argumentation, and Games. He is a Fellow of the British Computer Society and a College Member of the EPSRC. He has been organizer of the European Agent Systems Summer School (EASSS), the Conference on Logics for Games and Decision Theory (LOFT), and the Conference on Logics for AI (JELIA), and he is Editor-in-Chief of Knowledge, Rationality and Action and Managing Editor of a new bookseries Texts in Logic and Games.