▾ Set of symbols
▾ Alphabet
▾ Deduction system
▾ Theory
▾ Zermelo-Fraenkel set theory
▾ Set
▾ Transitive set
Ordinal number
Formulation 0
An D548: Ordered pair $P = (X, {\in}_X)$ is an ordinal number if and only if
(1) $X$ is a D666: Transitive set
(2) ${\in}_X$ is the D1943: Membership relation on $X$
(3) $P$ is a D1124: Well-ordered set
Also known as
Ordinal
Child definitions
» D686: Class of ordinal numbers