Doherty, Patrick Lukaszewicz, Witold Szalas, Andrzej 1996 (English)In: Fundamenta Informaticae, ISSN 0169-2968, Vol. 28, no 3,4, 261-272Artikel i tidskrift (Refereed) Published
Circumscription has been perceived as an elegant mathematical technique for modeling nonmonotonic and commonsense reasoning, but difficult to apply in practice due to the use of second-order formulas. One proposal for dealing with the computational problems is to identify classes of first-order formulas whose circumscription can be shown to be equivalent to a first-order formula. In previous work, we presented an algorithm which reduces certain classes of second-order circumscription axioms to logically equivalent first-order formulas. The basis for the algorithm is an elimination lemma due to Ackermann. In this paper, we capitalize on the use of a generalization of Ackermann's Lemma in order to deal with a subclass of universal formulas called semi-Horn formulas. Our results subsume previous results by Kolaitis and Papadimitriou regarding a characterization of circumscribed definite logic programs which are first-order expressible. The method for distinguishing which formulas are reducible is based on a boundedness criterion. The approach we use is to first reduce a circumscribed semi-Horn formula to a fixpoint formula which is reducible if the formula is bounded, otherwise not. In addition to a number of other extensions, we also present a fixpoint calculus which is shown to be sound and complete for bounded fixpoint formulas.
National CategoryComputer Science
Identifiersurn:nbn:se:liu:diva-41621 (URN)10.3233/FI-1996-283404 (DOI)2-s2.0-0030383468 (ScopusID)58414 (Local ID)oai:DiVA.org:liu-41621 (OAI)