Jabarkan 2 ∈ A dari Elemen (matematika)

{3,4} adalah anggota dari B

- "Naive" means that it is not fully axiomatized, not that it is silly or easy (Halmos's treatment is neither).

- Both the notion of set (a collection of members), membership or element-hood, the axiom of extension, the axiom of separation, and the union axiom (Suppes calls it the sum axiom) are needed for a more thorough understanding of "set element".