**singleton set**if and only if \begin{equation} |X| = 1 \end{equation}

▾ Set of symbols

▾ Alphabet

▾ Deduction system

▾ Theory

▾ Zermelo-Fraenkel set theory

▾ Set

▾ Transitive set

▾ Ordinal number

▾ Cardinal number

▾ Set cardinality

▾ Alphabet

▾ Deduction system

▾ Theory

▾ Zermelo-Fraenkel set theory

▾ Set

▾ Transitive set

▾ Ordinal number

▾ Cardinal number

▾ Set cardinality

Formulation 0

A D11: Set $X$ is a **singleton set** if and only if
\begin{equation}
|X| = 1
\end{equation}

Also known as

Enton set

Child definitions

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