Agreeing to disagree

Robert Aumann

pp. 859-862

in: Horacio Arló-Costa, Vincent F. Hendricks, Johan van Benthem (eds), Readings in formal epistemology, Berlin, Springer, 2016

Abstract

Two people, 1 and 2, are said to have common knowledge of an event E if both know it, 1 knows that 2 knows it, 2 knows that 1 knows it, 1 knows that 2 knows that 1 knows it, and so on.Theorem If two people have the same priors, and their posteriors for an event A are common knowledge, then these posteriors are equal.