| dc.description.abstract | "Non-monotonic" logical systems are logics in  which the introduction of new axioms can  invalidate old theorems. Such logics are very  important in modeling the beliefs of active  processes which, acting in the presence of  incomplete information, must make and  subsequently revise predictions in light of new  observations. We present the motivation and  history of such logics. We develop model and  proof theories, a proof procedure, and  applications for one important non-monotonic  logic. In particular, we prove the  completeness of the non-monotonic predicate  calculus and the decidability of the non-monotonic sentential calculus. We also  discuss characteristic properties of this logic  and its relationship to stronger logics, logics  of incomplete information, and truth  maintenance systems. | en_US |