Revision by comparison as a unifying framework: Severe withdrawal, irrevocable revision and irrefutable revision

Fermé and Rott [Revision by comparison, Art. Intell. 157 (2004) 5–47] introduced a binary operation of ‘revision by comparison’ and pointed out that this method of changing epistemic states has both characteristics of belief contraction (with respect to the ‘reference sentence’) and characteristics of belief revision (with respect to the ‘input sentence’). Using revision by comparison as a unifying framework, the present paper studies the unary limiting cases of severe withdrawal, irrevocable revision and irrefutable revision. While variants of the first two operations are well-known from the literature, the last one is new.