When giving an nalysis of knowledge in multiagent systems, one needs a framework in which higher-order information and its dynamics can both be represented. A recent tradition stoxting in origina work by Plaza treats all of knowledge, higher-order knowledge, and its dynamics on the sae foot. Our work is in that tradition. It also fits in approaches that not only dynaize the epistemics, but also epistemize the dynamics: the ac- tions that (groups of) agents perform oxe epistemic actions. Different agents may have different information about which action is taking place, including higher-order information. We demonstrate that such information changes require subtle descriptions. Our contribution is to provide a complete axiomatization for n action language of vn Ditmoxsch, where an action is interpreted as a relation between epistemic states (pointed models) and sets of epistemic states. The applicability of the framework is found in every context where multiagent strategic decision making is at stake, and aready demonstrated in gae-like scenoxios such as Cluedo and coxd games.

To describe simultaneous knowledge updates for different subgroups we propose an epistemic language with dynamic operators for actions. The language is interpreted on equivalence states (S5 states). The actions are interpreted as state transformers. Two crucial action constructors are learning and local choice. Learning is the dynamic equivalent of common knowledge. Local choice aids in constraining the interpretation of an action to a functional interpretation (state transformer). Bisimilarity is preserved under execution of actions. The language is applied to describe various actions in card games.

We present a model-theoretic approach for reasoning about security protocols, applying recent insights from dynamic epistemic logics. This enables us to describe exactly the subsequent epistemic states of the agents participating in the protocol, using Kripke models and transitions between these based on updates of the agents' beliefs associated with steps in the protocol. As a case study we will consider the SRA Three Pass protocol and discuss the Wide-Mouthed Frog protocol. 1.