Eliminating the Fixed Predicates from a Circumscription

Abstract Parallel predicate circumscription is the primary circumscriptive technique used in formalizing commonsense reasoning. In this paper we present a direct syntactic construction for transforming any parallel predicate circumscription using fixed predicates into an equivalent one which does not. Thus, we show that predicate circumscription is no more expressive with fixed predicates than without. We extend this result to prioritized circumscription. These results are expected to be useful for comparing circumscription to other nonmonotonic formalisms (such as autoepistemic logic and assumption-based truth maintenance) and for implementing fixed predicates.