Example image of eyePlorer eyePlorer map for 'Axiom of union': Axiom of extensionality Existential quantification Formal language If and only if Logical conjunction Set (mathematics) Union (set theory) Universal quantification Axiomatic system Intersection (set theory) Axiom schema of specification Empty set Universal set Paul Halmos Axiom of infinity Constructive set theory Kripke–Platek set theory Kripke–Platek set theory with urelements Zermelo set theory Quasi-set theory Axiom of pairing General set theory Morse–Kelley set theory Von Neumann–Bernays–Gödel set theory Constructible universe Zermelo–Fraenkel set theory Implementation of mathematics in set theory Naive set theory Ordinal number