Revision and updating in dynamic doxastic logic

The topic of the paper is the introduction of an update-operator in the sense of Katsuno and Mendelzon (1992) into dynamic doxastic logic developed by Segerberg (1995). Dynamic doxastic logic (DDL) was introduced as a tool for analyzing rational theory change, taking its starting point in the AGM-approach to belief revision. AGM deals with change of information about a static world. But there is another kind of theory change, namely, change of information triggered by changes in the (dynamic) world. This kind of theory change was analyzed by several authors, who called it “updating”. The author proposes a first step in an analysis of updating in the framework of DDL by introducing a primitive update operator in the language of DDL and interpreting it in a semantics which is a simple extension of hypertheory-semantics. It is shown that this operator is an update-operator in the sense of Katsuno and Mendelzon