The lexicographic closure of any given finite set D of normal defaults is defined. A conditional assertion a b is in this lexicographic closure if, given the defaults D and the fact a, one would conclude b. The lexicographic closure is essentially a rational extension of D, and of its rational

Abstract. Disjunctive Deductive Databases (DDDBs)-- function-free disjunctive logic programs with negation in rule bodies allowed-- have been recently recognized as a powerful tool for knowledge representation and commonsense reasoning. Much research as been spent on issues like semantics

soundness and completeness. The wide range of novel and adapted optimisation techniques employed by FaCT is also described and their effectiveness is evaluated by extensive empirical testing using both a large realistic knowledge base (from the GALEN project) and randomly generated satisfiability problems

skeptical mode of default reasoning. Our logic is based on the concept of a skeptical rational extension. We give characterization results for skeptical rational extensions and an algorithm to compute them. We present some complexity results. Our main goal is to characterize cases when the class

reasoning; the review of logics of dialogue and proposed extensions; and the pre-formal and initial formal discussion of aspects and variations of dialectical systems with non-demonstrative reasons. 1. ARGUMENTS AND DEMONSTRATION

Modal logic is the foundation for a versatile and well-established class of knowledge representation for-malisms in artificial intelligence. Enriching modal logics with non-monotonic reasoning capabilities such as preferential reasoning as developed by Lehmann and colleagues would therefore

Abstract. In this paper we describe a language for reasoning about actions that can be used for modelling and for programming rational agents. We propose a modal approach for reasoning about dynamic domains in a logic programming setting. Agent behavior is specified by means of complex actions

To what extent is the logic of rational belief an extension of classical logic? Bayesians explicate the notion of rational belief via the theory of subjective probability, and the axioms of probability imply that logical truths (respectively falsehoods) are given probability 1 (respectively 0

The default nonmonotonic reasoning was formalised by a class of logical systems: default logics (classical, justified, constrained, rational), based on the same syntax which utilises nonmonotonic inference rules: defaults, but with diffent semantics for the defaults. In this paper we introduce a

Abstract. We propose a new version of ATLP (“ATL with plausibility”), a logic for reasoning about the outcome of rational play in game-like scenarios. Unlike in [8], where two different extensions of ATL were used for specifying rationality and reasoning about agents ’ behavior, we now propose