Non-horn magic sets to incorporate top-down inference into bottom-up theorem proving

Abstract

We present a new method, called non-Horn magic sets (NHM), to enhance forward reasoning provers by combining top-down and bottom-up computations. This method is a natural extension of Horn magic sets and is applicable to range-restricted non-Horn clauses. We show two types of transformations to get non-Horn magic sets from the given clause sets: breadth-first NHM and depth-first NHM. The first transformation evaluates the antecedent atoms of an original clause in parallel. The second one evaluates them sequentially while propagating the bindings in an antecedent atom to the next by using continuation predicates. These transformations are shown to be sound and complete. The NHM method has been implemented on a UNIX workstation. We evaluated effects of NHM by proving some typical problems taken from the TPTP problem library.