Belief revision and belief update are two different forms of belief change, and they serve different purposes. In this paper we focus on belief update, the formalization of change in beliefs due to changes in the world. The complexity of the basic update (introudced by Winslett (1990)) has been determined in (Eiter and Gottlob, 1992). Since then, many other formalizations have been proposed to overcome the limitations and drawbacks of Winslett's update. In this paper we analyze the complexity of the proposals presented in the literautre, and relate some of them to previous work on closed world reasoning.
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