 The theories and operators we have seen so far all concern static belief change. We now wish to turn to dynamic belief change. For this the approach follows the typical pattern in Dynamic Epistemic Logic: we take a given static theory (in this case \(\KBox\)) and we add action model-style modalities to create the dynamic theory. When we did this before in the case of basic multi-modal epistemic and doxastic logic, the relational structure of the added action models matched the relational structure of the models of the theory—Kripke models. The structural match between action models and finite Kripke models is not accidental: the semantics of action model modalities (as explained by the  BMS product update)  uses the same Kripke model-based notion of agent uncertainty over objects (i.e., the “worlds”) to describe agent uncertainty over action model objects (i.e., the “events”). Both uncertainties are represented using the same kind of structure: the binary possibility relation \(R_a\). 