Joseph Y. Halpern
Professor
Codirector: 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 multiagent systems. The work uses tools from logic
(particularly modal logic and the idea of possibleworlds 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
Professional Activities
Editorinchief: 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
Settheoretic completeness for epistemic and
conditional logic. Fifth Int. Symp. Artificial Intelligence and Mathematics, Fort
Lauderdale, Jan. 1998.
Using multiagent 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, 12 (1998), 317349 (with R. Brafman and Y. Shoham).
Settheoretic 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), 6696.
On the expected value of games with
absentmindedness. Games and Economic Behavior 20 (1997), 5165 (with A. J. Grove).
Knowledgebased programs. Distributed Computing
10, 4 (1997), 199225 (with R. Fagin, Y. Moses, and M.Y. Vardi).
Modeling belief in dynamic systems. Part I:
Foundations. Artificial Intelligence 95, 2 (1997), 257316 (with N. Friedman).
Defining relative likelihood in partiallyordered
preferential structures. J. AI Research 7 (1997), 124.
Probability update: conditioning vs.
crossentropy. Proc. Thirteenth Conf. Uncertainty in AI, (1997), 208214 (with A.
J. Grove).
Defining explanation in probabilistic systems. Proc.
Thirteenth Conf. Uncertainty in AI, (1997), 6271 (with U. Chajewska).
Using multiagent systems to represent uncertainty
(summary of invited talk). SCAI '97 Proc. Sixth Scandinavian Conf. Artificial
Intelligence (1997), 14.
