AGM belief revision cannot clearly express iterated belief (BBp) because membership in a belief set does not straightforwardly encode higher-order belief

Epistemic logic, which in its modern formulation is typically traced to von Wright (1951) and Hintikka (1962), is a formal framework designed to foreground these matters. For an influential introductory text, see Fagin et al. (1995). The formal language of epistemic logic extends that of propositional logic with epistemic operators \({\bf B}_a \phi\) and \({\bf K}_a \phi\), pronounced respectively as ‘agent \(a\) believes that \(\phi\),’ and ‘agent \(a\) knows that \(\phi.\)’ When only one agent