Joseph Y. Halpern Professor Co-director: Cognitive Studies Program halpern@cs.cornell.edu http://www.cs.cornell.edu/home/halpern PhD Harvard, 1981 My research is concerned with representing and reasoning about knowledge and uncertainty in multi-agent systems. The work uses tools from logic (particularly modal logic and the idea of possible-worlds semantics), probability theory, distributed systems, game theory, and AI, and I like to think that the work contributes to our understanding of each of these areas as well.

Some themes of my current research include: (1) defining useful notions of explanation in probabilistic systems, (2) providing foundations for useful qualitative notions of decision theory, and (3) applying ideas of decision theory to constructing algorithms in asynchronous distributed systems.

University Activities

• Co-director: Cognitive Studies Program

• Recruiting Committee: Electrical Engineering

Professional Activities

• Editor-in-chief: J. ACM

• Consulting Editor: Chicago J. Computer Science

• Editorial board: Artificial Intelligence J., Information and Computation; J. Logic and Computation

• ACM Publications Board Chair:

• Preprint Repository Project

• LICS (IEEE Conf. Logic in Computer Science) Advisory Board

• Conference Chair: 7th Conf. Theoretical Aspects of Rationality and Knowledge

• President of Board of Directors: Corp. for Theoretical Aspects of Reasoning About Knowledge

Lectures

• Set-theoretic completeness for epistemic and conditional logic. Fifth Int. Symp. Artificial Intelligence and Mathematics, Fort Lauderdale, Jan. 1998.

• Using multi-agent systems to represent uncertainty. Fifth Int. Symp. Artificial Intelligence and Mathematics, Fort Lauderdale, Jan. 1998.

• ___. Univ. Rochester, Rochester, Dec. 1997.

• ___. Sixth Scandinavian Conf. Artificial Intelligence (SCAI), Helsinki, Finland, Aug. 1997.

• Knowledge and common knowledge in a distributed environment. Invited lecture. Workshop on Bounded Rationality and Default Reasoning in Epistemic Logic and Artificial Intelligence with Applications to Economics and Game Theory, Florence, Italy, July 1997.

• Approaches to the logical omniscience problem. Invited lecture. Ibid.

• Plausibility measures: A uniform approach to counterfactuals, default reasoning, and belief change. Invited lecture. Ibid.

Publications

• On the knowledge requirements for tasks. Artificial Intelligence 98, 1-2 (1998), 317-349 (with R. Brafman and Y. Shoham).

• Set-theoretic completeness for epistemic and conditional logic. Proc. Fifth Int. Symp. Artificial Intelligence and Mathematics (1998).

• On ambiguities in the interpretation of game trees. Games and Economic Behavior 20 (1997), 66-96.

• On the expected value of games with absentmindedness. Games and Economic Behavior 20 (1997), 51-65 (with A. J. Grove).

• Knowledge-based programs. Distributed Computing 10, 4 (1997), 199-225 (with R. Fagin, Y. Moses, and M.Y. Vardi).

• Modeling belief in dynamic systems. Part I: Foundations. Artificial Intelligence 95, 2 (1997), 257-316 (with N. Friedman).

• Defining relative likelihood in partially-ordered preferential structures. J. AI Research 7 (1997), 1-24.

• Probability update: conditioning vs. cross-entropy. Proc. Thirteenth Conf. Uncertainty in AI, (1997), 208-214 (with A. J. Grove).

• Defining explanation in probabilistic systems. Proc. Thirteenth Conf. Uncertainty in AI, (1997), 62-71 (with U. Chajewska).

• Using multi-agent systems to represent uncertainty (summary of invited talk). SCAI '97 Proc. Sixth Scandinavian Conf. Artificial Intelligence (1997), 1-4.