ThmDex – An index of mathematical definitions, results, and conjectures.
Set of symbols
Alphabet
Deduction system
Theory
Zermelo-Fraenkel set theory
Set
Transitive set
Ordinal number
Cardinal number
Set cardinality
Definition D135
Singleton set
Formulation 0
A D11: Set $X$ is a singleton set if and only if \begin{equation} |X| = 1 \end{equation}
Children
Duoton set
Set of singletons