Recent contributions have questioned the meaningfulness of the Common Prior Assumption (CPA) in situations of incomplete information. We characterize the CPA in terms of the primitives (individuals' belief hierarchies) without reference to an ex ante stage. The key is to rule out "agreeing to...

We provide a general notion of perfect Bayesian equilibrium which can be applied to arbitrary extensive-form games and is intermediate between subgame-perfect equilibrium and sequential equilibrium. The essential ingredient of the proposed definition is the qualitative notion of AGM-consistency,...

Given an extensive form "G", we associate with every choice an atomic sentence and with every information set a set of well-formed formulas (wffs) of propositional calculus. The set of such wffs is denoted by [Gamma](G). Using the so-called topological semantics for propositional calculus (which...