Papers

Rewrite-based equational theorem proving with selection and simplification

Journal of Logic and Computation, 4(3), pp. 1-31, 1994

This paper develops the theoretical basis of the superposition calculi.

Abstract. We present various refutationally complete calculi for first-order clauses with equality that allow for arbitrary selection of negative atoms in clauses. Refutation completeness is established via the use of well-founded orderings on clauses for defining a Herbrand model for a consistent set of clauses. We also formulate an abstract notion of redundancy and show that the deletion of redundant clauses during the theorem proving process preserves refutation completeness. It is often possible to compute the closure of nontrivial sets of clauses under application of non-redundant inferences. The refutation of goals for such complete sets of clauses is simpler than for arbitrary sets of clauses, in particular one can restrict attention to proofs that have support from the goals without compromising refutation completeness. Additional syntactic properties allow to restrict the search space even further, as we demonstrate for so-called quasi-Horn clauses. The results in this paper contain as special cases or generalize many known results about Knuth-Bendix-like completion procedures (for equations, Horn clauses, and Horn clauses over built-in Booleans), completion of first-order clauses by clausal rewriting, and inductive theorem proving for Horn clauses.

Proc. 9th IEEE Symposium on Logic in Computer Science, 1994

This paper develops the theoretical basis of the generalization of the superposition calculi into chaining calculi.

Abstract. We propose inference systems for dealing with transitive relations in the context of resolution-type theorem proving. These inference mechanisms are based on standard techniques from term rewriting and represent a refinement of chaining methods. We establish their refutational completeness and also prove their compatibility with the usual simplification techniques used in rewrite-based theorem provers. A key to the practicality of chaining techniques is the extent to which so-called variable chainings can be restricted. We demonstrate that rewrite techniques considerably restrict variable chaining, though we also show that they cannot be completely avoided for transitive relations in general. If the given relation satisfies additional properties, such as symmetry, further restrictions are possible. In particular, we discuss (partial) equivalence relations and congruence relations.

12th International Conference on Automated Deduction Nancy, France, 1994

This paper develops the theoretical basis of the specialized chaining calculi for total orderings.

Abstract. We propose inference systems based on ordered chaining and a concept of (global) redundancy for clauses and inferences for dealing with total orderings. A key to the practicality of chaining techniques is the extent to which so-called variable chainings can be restricted. We demonstrate that ordering restrictions and the rewrite techniques which account for their completeness considerably restrict variable chaining. For dense total orderings we show that the techniques for eliminating unshielded variables are admissible simplifications so that no variable chaining is needed at all. We also include equality by combining ordered chaining with superposition.

This paper explains version 1.0 of the Saturate system with an emphasis on the various proof techniques for redundancy that have been implemented