 In the dominant theory of belief revision, the so-called AGM model, the set representing the belief state is assumed to be a logically closed set of sentences (a belief set). One of most debated topics in belief revision theory is the recovery postulate, according to which all the original beliefs are regained if one of them is first removed and then reinserted. The recovery postulate holds in the AGM model but not in closely related models employing belief bases. Another much discussed topic is how repeated changes can be adequately represented. Several alternative models have been proposed that are intended to provide a more realistic account of belief change than that offered by the AGM model. 