Two Methods of Constructing Contractions and Revisions of Knowledge Systems

摘要: The theory of nonmonotonic reasoning and the belief revision share a very important subject. Both theories help to understand how it is possible rationally pass from one knowledge system into another that in contradiction with former one. In this transition accomplished by distinguishing between axioms ("explicit beliefs") theorems ("implicit giving up doctrine more must always yield theorems. Thus my old (implicit) Tweety can fly may well turn disbelief after getting information (acquiring explicit belief) penguin. A considerable limitation approach new axiom be (monotonica!ly) consistent previous axioms, or else we get an inconsistent base. on which I shall focus attention not subject restriction. fact, does at all distinguish theorems, beliefs their reasons. systems takes consideration are whole theories, where theory, set, understood as set sentences closed under some appropriate logic Cn. We assume includes classical propositional logic, compact (i.e., if