Two currently active strands of research on logics for multi-agent systems are dynamic epistemic logic, focusing on the epistemic consequences of actions, and logics of coalitional ability, focusing on what coalitions of agents can achieve by cooperating strategically. In this paper we make a first attempt to bridge these topics by considering the question: "what can a coalition achieve by public announcements?". We propose, first, an extension of public announcement logic with constructs of the form  φ, where G is a set of agents, with the intuitive meaning that G can jointly make an announcement such that φ will be true afterwards. Second, we consider a setting where all agents can make (truthful) announcements at the same time, and propose a logic with a construct  φ, meaning that G can jointly make an announcement such that no matter what the other agents announce, φ will be true. The latter logic is closely related to Marc Pauly's Coalition Logic.
['Thomas Ågotnes', 'Hans van Ditmarsch']
Coalitions and announcements