SOUNDNESS OF ABDUCTIVE PROOF PROCEDURE WITH RESPECT TO CONSTRAINT FORNON-GROUND ABDUCIBLES

Eshghi and Kowalski's abductive procedure is not, in general, sound wi th respect to the 2-valued stable model semantics, but sound with resp ect to preferred extension (Dung, 1991). We establish an abduction fra mework in which the integrity constraint is defined so that non-ground abducibles may be extracted. By dealing with alternating fixpoint the ory as in Van Gelder (1993) on the domain containing variables, we sho w, with respect to the proposed constraint, the soundness of a modifie d version of Eshghi and Kowalski's procedure where the negation as fai lure with non-safe rule is adopted. (C) 1998-Elsevier Science B.V. All rights reserved.