Mutual Belief Revision (Preliminary Report)

A semantical theory of belief revision in synchronous multi-agent systems is presented. The theory assumes that the world is static, and that the belief revision methods used by the agents are common knowledge. It is shown that the theory has as a special case the revision of knowledge in a broadcast variant of Fagin and Vardi's communicating scientists model, in which knowledge is deened in terms of an equivalence relation on runs in a distributed system. Next, the theory is applied to give a semantic reconstruction of a default logic theory of speech acts proposed by Perrault. This reconstruction characterizes the way the speech act transforms an only knowing representation of the agent's belief states. The results are shown to diier from those obtained by Perrault. In particular , it is argued that a sincere assertion does not necessarily lead to mutual belief of the proposition asserted, even when the hearer does not initially have any beliefs about this proposition.