Definition: The statement (e ELMT g) indicates that the entity e is a member of the collection g, i.e. ELMT corresponds to the element relation of naive set theory. Consequently, g ∈ pe(n+1) must be a set (preextensional entity) of order n+1 compared to the element e ∈ pe(n), which is of order n. In particular, if e is an individual (or a set) then g has to be a set (or a family of sets).