Semantic Resolution for Horn Sets

A new resolution strategy for Horn sets of clauses, each clause of which contains no more-than one positive literal, is presented which requires that in each resolution either one ancestor be a false positive unit or that one ancestor and the resolvent both be false. This strategy emphasizes "relevant" positive units while controlling the explosive nonunit resolution. Some properties of interpretations for Horn sets are reviewed and used to significantly reduce the computation and storage required to implement semantic resolution for Horn sets.