A theorem prover for default logic based on prioritized conflict resolution and an extended resolution principle

Abstract

This paper presents a theorem prover for Reiter's default logic, one of the most studied nonmonotonic logics. Our theorem prover is based on a decomposition of default logic into two main elements: we describe an extension of the resolution principle, that handles the “monotonic” aspect of the defaults, and we provide a generalization of Reiter's and Levy's algorithms for the computation of hitting sets, that takes care of the nonmonotonic part of default logic. Lastly, we describe how these two components can be separately modified in order to obtain theorem provers for other variants of default logic, notably prioritized default logic.