Private announcement and belief expansion: an internal perspective (Q2893319)

This paper is a study in the transposition of notions from agentless logics to multi-agent ones. Specifically, it considers possible articulations of the notion of expansion (simple closure under classical consequence of a belief set plus input proposition, without any consistency constraints) in the multi-agent context formalized by the dynamic epistemic logic of Baltag, Moss and Solecki (aka the BMS framework). The author sees the most natural generalization to be private announcement, contrary to the perspective of some authors, who have seen it rather as public announcement. A companion paper [the author, Log. J. IGPL 18, No. 4, 530--558 (2010; Zbl 1203.03022)] takes up the question of transposing the AGM notion of belief revision to a multi-agent context.