Agreeing to disagree: The non-probabilistic case

A non-probabilistic generalization of Aumann’s (1976) agreement theorem is proved. Early attempts at such a theorem were based on a version of the sure-thing principle which assumes an intrapersonal-interstate comparison of knowledge. But such comparisons are impossible in partition structures. The theorem proved here is based on a new version of the sure-thing principle that makes an interpersonal-intrastate comparison of knowledge.