On information functions. Part Two : Applications to the logic of theory change

Abstract

The purpose of this work is to show how the notion of information function introduced in [1] can be used in the logic of theory change developed by P. Gardenfors, C. E. Alchourron and D. Makinson in [2], [3] and [4]. The simplest and best known form of theory change is expansion, where a new position, if consistent with a given theory K, is set-theoretically added to K and this expanded set is then closed under logical consequence. Second form is theory contraction, where a proposition a, which was earlier in a theory K , is rejected. The basic problem is to determine which propositions should be rejected along with a so that the contracted theory will be closed under logical consequence. Third kind of change is revision, where a proposition, in general inconsistent with a given theory K, is added to K under the requirement that the revised theory be consistent and closed under logical consequence (Fragment tekstu).