Joseph Y. Halpern

Introduced reasoning about knowledge to the study of computing. He thinks about computing processes as actors that know facts. This novel perspective he introduced became a standard framework for establishing the correctness of complex distributed systems. He showed that there are forms of knowledge that all participants in a system may possess at the outset that can never become common knowledge. He developed fundamental tools for reasoning about a range of notions, including awareness, belief, causality, uncertainty, and imperfect recall. His work shaped the area of multi-agent systems, and the interface between computer science and economics.