A Dynamic Informational-Epistemic Logic

Epistemic logic is usually employed to model two aspects of a situation: the ontic and the epistemic aspects. Truth, however, is not always attainable, and in many cases we are forced to reason only with whatever information is available to us. In this paper, we will explore a four-valued epistemic logic designed to deal with situations of this sort. The technical results include a set of reduction axioms for public announcements, correspondence proofs, and a complete tableau system