An alternative approach to modeling beliefs was initiated by Harsanyi in his seminal paper (Harsanyi 1967–68). Rather than “possible worlds”, Harsanyi takes the notion of the players’ type as primitive. Formally, the players are assigned a nonempty set of types. Typically, players are assumed to know their own type but not the types of the other players. As we will see, each type can be associated with a specific hierarchy of belief