Abstract

Sven-Ove Hansson and Erik Olsson studied in [7] the logical properties of an operation of contraction first proposed by Isaac Levi in [10]. They provided a completeness result for the simplest version of contraction that they call Levicontraction but left open the problem of characterizing axiomatically the more complex operation of value-based contraction or saturatable contraction. In this paper we propose an axiomatization for this operation and prove a completeness result for it. We argue that the resulting operation is better behaved than various rival operations of contraction defined in recent years.