We propose a variant of ordered resolution with semantic restrictions based on interpretations which are identi ed by the given atom ordering and selection function. Techniques for effectively approximating validity (satisfiability) in these interpretations are presented. They are related to methods of soft typing for programming languages. The framework is shown to be strictly more general than certain previously introduced approaches. Implementation of some of our techniques in the Spass prover has lead to encouraging experimental results.

We show that unification in certain extensions of shallow equational theories is decidable. Our extensions generalize the known classes of shallow or standard equational theories. In order to prove decidability of unification in the extensions, a class of Horn clause sets called sorted shallow equational theories is introduced. This class is a natural extension of tree automata with equality constraints between brother subterms as well as shallow sort theories. We show that saturation under sorted superposition is effective on sorted shallow equational theories. So called semi-linear equational theories can be e ectively transformed into equivalent sorted shallow equational theories and generalize the classes of shallow and standard equational theories.

We give a set of inference rules for E-unification, similar to the inference rules for Syntactic Mutation. If the E is finitely saturated by paramodulation, then we can block certain terms from further inferences. Therefore,