Extensive Games with Possibly Unaware Players

Abstract: Standard game theory assumes that the structure of the game is common knowledge among players. We relax this assumption by considering extensive games where agents may be unaware of the complete structure of the game. In particular, they may not be aware of moves that they and other agents can make. We show how such
games can be represented; the key idea is to describe the game from the point of view of every agent at every node of the game tree. We provide a generalization of Nash equilibrium and show that every game with awareness has a generalized Nash equilibrium. Finally, we extend these results to games with awareness of unawareness,
where a player $i$ may be aware that a player j can make moves that i is not aware of and to subjective games, where players may have no common knowledge regarding the actual game.

This is joint work with Leandro Rego.

Papers: paper1, paper2.


Biography:  Joseph Y. Halpern received a B.Sc. in mathematics from the University of Toronto in 1975 and a Ph.D. in mathematics from Harvard in 1981. In between, he spent two years as the head of the Mathematics Department at Bawku Secondary School, in Ghana. After a year as a visiting scientist at MIT, he joined the IBM Almaden Research Center in 1982, where he remained until 1996. He served as manager of the Mathematics and Related Computer Science Department at IBM from 1988-1990 and was a consulting professor at Stanford from 1984-1996. In 1996, he moved to Cornell University, where he is a professor in Computer Science.

His major research interests are in reasoning about knowledge and uncertainty, qualitative reasoning, causality, belief revision, (fault-tolerant) distributed computation, game theory, decision theory, and security. Together with his former student, Yoram Moses, he pioneered the approach of applying reasoning about knowledge to analyzing distributed protocols and multi-agent systems. He has coauthored 5 patents, two books ("Reasoning About Knowledge" and "Reasoning about Uncertainty"), and well over 100 journal publications and 100 conference publications. He was designated Highly Cited Researcher by the Institute for Scientific Information.

Halpern was program chair and organizer of the first conference on Theoretical Aspects of Reasoning about Knowledge, and program chair of the 5th ACM Symposium on Principles of Distributed Computing, the 23rd ACM Symposium on Theory of Computing, and the 16th IEEE Symposium on Logic in Computer Science. He received the Publishers' Prize for Best Paper at at the International Joint Conference on Artificial Intelligence in 1985 (joint with Ronald Fagin) and in 1989, the 1997 Godel Prize (joint with Yoram Moses), and two IBM Outstanding Innovation Awards. He is a Fellow of AAAI (American Association of Artificial Intelligence), AAAS (American Association for the Advancement of Science), and ACM (Association for Computing Machinery), and in 2001-02 was the recipient of a Guggenheim and a Fulbright Fellowship. He was editor-in-chief of Journal of the ACM, and currently serves on the editorial board of Journal of Logic and Computation, Games and Economic Behavior, and Artificial Intelligence.


Joseph Halpern