Controlled Use of Clausal Lemmas in Connection Tableau Calculi

Proof procedures based on model elimination or the connection tableau calculus have become more and more successful. But these procedures still suffer from long proof lengths as well as from a rather high degree of redundant search effort in comparison with resolution-style search procedures. In order to overcome these problems we investigate the use of clausal lemmas. We develop a method to augment a given set of clauses by a lemma set in a preprocessing phase and discuss the ability of this technique to reduce proof lengths and depths and to provide an appropriate reordering of the search space. We deal with the basic connection tableau calculus as well as with several calculus refinements and extensions. In order to control the use of lemmas we develop techniques for selecting relevant lemmas based on partial evaluation techniques. Experiments with the proverSetheo performed in several domains demonstrate the high potential of our approach.