D New algorithms for deciding whether a (propositional) Horn formula is satisfiable are presented. If the Horn formula A contains K distinct propositional letters and if it is assumed that they areâ€¦ (More)

In this paper, it is shown that the method of matings due toAndrews and Bibel can be extended to (first-order) languages withequality. A decidable version of<?Pub Fmt italic>E<?Pub Fmtâ€¦ (More)

This paper is concerned with E-unification in arbitrary equational theories. We extend the method of transformations on systems of terms, developed by Martelli-Montanari for standard unification, toâ€¦ (More)

In this paper, we reexamine the problem of general higher-order unification and develop an approach based on the method of transformations on systems of terms which has its roots in Herbrandâ€™sâ€¦ (More)

This paper consists primarily of a survey of results of Harvey Friedman about some proof theoretic aspects of various forms of Kruskalâ€™s tree theorem, and in particular the connection with theâ€¦ (More)

Rigid E-unification is a restricted kind of unification modulo equational theories, or E-unification, that arises naturally in extending P. Andrews' (1981) theorem-proving method of mating toâ€¦ (More)