Episteme
"Episteme" is a philosophical term derived from the Ancient Greek word ἐπιστήμη "epistēmē", which can refer to knowledge, science or understanding, and which comes from the verb , meaning "to know, to understand, or to be acquainted with".
Dynamic epistemic logic
Epistemic logic is a modal logic. So, what we call an epistemic model formula_73 is just a Kripke model as defined in modal logic. The set formula_74 is a non-empty set whose elements are called "possible worlds" and the "interpretation" formula_75 is a function specifying which propositional facts (such as ‘Ann has the red card’) are true in each of these worlds. The "accessibility relations" formula_76 are binary relations for each agent formula_77; they are intended to capture the uncertainty of each agent (about the actual world and about the other agents' uncertainty). Intuitively, we have formula_78 when the world formula_79 is compatible with agent formula_39’s information in world formula_81 or, in other words, when agent formula_39 considers that world formula_79 might correspond to the world formula_81 (from this standpoint). We abusively write formula_85 for formula_86 and formula_87 denotes the set of worlds formula_88.