Vladimir Lifschitz

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An important limitation of traditional logic programming as a knowledge representation tool, in comparison with classical logic, is that logic programming does not allow us to deal directly with incomplete information. In order to overcome this limitation, we extend the class of general logic programs by including classical negation, in addition to(More)
Knowledge Interchange Format (KIF) is a computer-oriented language for the interchange of knowledge among disparate programs. It has declarative semantics (i.e. the meaning of expressions in the representation can be understood without appeal to an interpreter for manipulating those expressions); it is logically comprehensive (i.e. it provides for the(More)
The nonmonotonic causal logic defined in this paper can be used to represent properties of actions, including actions with conditional and indirect effects, nondeterministic actions, and concurrently executed actions. It has been applied to several challenge problems in the theory of commonsense knowledge. We study the relationship between this formalism(More)
In many cases a logic program can be divided into two parts so that one of them the bottom part does not refer to the predicates de ned in the top part The bottom rules can be used then for the evaluation of the predicates that they de ne and the computed values can be used to sim plify the top de nitions We discuss this idea of splitting a program in the(More)
Circumscription is a transformation of predicate formulas proposed by John McCarthy for the purpose of formalizing non-monotonic aspects of commonsense reasoning. Circumscription is difficult to implement because its definition involves a second-order quantifier. This paper presents metamathematical results that allow us in some cases to replace(More)
Answer set programming (ASP) is a form of declarative programming oriented towards difficult search problems. As an outgrowth of research on the use of nonmonotonic reasoning in knowledge representation, it is particularly useful in knowledge-intensive applications. ASP programs consist of rules that look like Prolog rules, but the computational mechanisms(More)