Can we compare models in terms of the number of substantive assumptions that are made? Are there models that make no, or at least as few as possible, substantive assumptions? These questions have been extensively discussed in the epistemic foundations of game theory—see the discussion in Samuelson (1992) and the references in Moscati (2009). Intuitively, a structure without any substantive assumptions must represent all possible states of (higher-order) information. Whether such a structure exists will depend, in part, on how the players’ informational attitudes are represented—e.g., as (conditional/lexicographic) probability measures or set-valued knowledge/belief functions. These questions have triggered interest in the existence of “rich” models containing most, if not all, possible configurations of (higher-order) knowledge and beliefs.