 In the AGM framework, there are three types of belief change. In contraction, a specified sentence \(p\) is removed, i.e., a belief set \(K\) is superseded by another belief set \(K\div p\) that is a subset of \(K\) not containing \(p\). In expansion a sentence \(p\) is added to \(K\), and nothing is removed, i.e. \(K\) is replaced by a set \(K+p\) that is the smallest logically closed set that contains both \(K\) and \(p\). In revision a sentence \(p\) is added to \(K\), and at the same time other sentences are removed if this is needed to ensure that the resulting belief set \(K* p\) is consistent.