Relativized common knowledge for dynamic epistemic logic

Relativized common knowledge is a generalization of common knowledge proposed for public announcement logic by treating knowledge update as relativization. Among other things relativized common knowledge, unlike standard common knowledge, allows reduction axioms for the public announcement operators. Public announcement logic can be seen as one of the simplest special cases of action model logic (AML). However, so far no notion of relativized common knowledge has been proposed for AML in general. That is what we do in this paper. We propose a notion of action model relativized common knowledge for action model logic, and study expressive power and complete axiomatizations of resulting logics. Along the way we fill some gaps in existing expressivity results for standard relativized common knowledge.