Robust Belief: \(B_i^r(E)=\{w \mid v\in E, \mbox{ for all } v \mbox{ with } w \preceq_i v\}\)  So, \(E\) is robustly believed if it is true in all worlds more plausible then the current world. This stronger notion of belief has also been called certainty by some authors (cf. Shoham &amp; Leyton-Brown 2008: sec. 13.7).