Circumscribing Defaults

Abstract

One of the questions in understanding the relation between circumscription and consistencybased nonmonotonic logic is- can default logic be expressed in circumscription? While it seems impossible to express default logic in existing forms of circumscription, is it nevertheless possible to express default logic in a certain extension of circumscription? This paper presents a construction of "default logic " in the spirit of circumscription. It has been shown that the new formalism, circumscriptive extension, is indeed an extension of circumscription. The equivalence of the new formalism and default logic is shown to hold under certain conditions, which demonstrates that default logic can be expressed by merely classical logic with a fixed point operator. 1