When I first participated in exploring theories of nonmonotonic reasoning in the late 1970s, I had no idea of the wealth of conceptual and mathematical results that would emerge from those halting first steps. This book by Wiktor Marek and Miroslaw Truszczynski is an elegant treatment of a large body of these results. It provides the first comprehensive treatment of two influen tial nonmonotonic logics - autoepistemic and default logic - and describes a number of surprising and deep unifying relationships between them. It also relates them to various modal logics studied in the philosophical logic litera ture, and provides a thorough treatment of their applications as foundations for logic programming semantics and for truth maintenance systems. It is particularly appropriate that Marek and Truszczynski should have authored this book, since so much of the research that went into these results is due to them. Both authors were trained in the Polish school of logic and they bring to their research and writing the logical insights and sophisticated mathematics that one would expect from such a background. I believe that this book is a splendid example of the intellectual maturity of the field of artificial intelligence, and that it will provide a model of scholarship for us all for many years to come. Ray Reiter Department of Computer Science University of Toronto Toronto, Canada M5S 1A4 and The Canadian Institute for Advanced Research Table of Contents 1 1 Introduction ........."

This volume contains the revised refereed papers accepted for presentation at the Third International Conference on Logic Programming and Nonmonotonic Reasoning, LPNMR '95, held in Lexington, KY, USA in June 1995 under the sponsorship of the Association for Logic Programming.
The LPNMR conferences bring together researchers from logic programming and the logical foundations of artificial intelligence in order to facilitate cooperation and cross-fertilization of ideas. The 28 full papers presented define the state of the art in this interdisciplinary area of research, which has recently attracted much interest.

This monograph provides a thorough analysis of two important formalisms for nonmonotonic reasoning: default logic and modal nonmonotonic logics. It is also shown how they are related to each other and how they provide the formal foundations for logic programming. The discussion is rigorous, and all main results are formally proved. Many of the results are deep and surprising, some of them previously unpublished. The book has three parts, on default logic, modal nonmonotonic logics, and connections and complexity issues, respectively. The study of general default logic is followed by a discussion of normal default logic and its connections to the closed world assumption, and also a presentation of related aspects of logic programming. The general theory of the family of modal nonmonotonic logics introduced by McDermott and Doyle is followed by studies of autoepistemic logic, the logic of reflexive knowledge, and the logic of pure necessitation, and also a short discussion of algorithms for computing knowledge and belief sets. The third part explores connections between default logic and modal nonmonotonic logics and contains results on the complexity of nonmonotonic reasoning. The ideas are presented with an elegance and unity of perspective that set a new standard of scholarship for books in this area, and the work indicates that the field has reached a very high level of maturity and sophistication. The book is intended as a reference on default logic, nonmonotonic logics, and related computational issues, and is addressed to researchers, programmers, and graduate students in the Artificial Intelligence community.