Definition:Doubleton
From ProofWiki
Definition
A doubleton is a set that contains exactly two elements.
The doubleton containing the elements $a$ and $b$ can be written $\left\{{a, b}\right\}$.
The set $\left\{{a, b}\right\}$ is known as the doubleton of $a$ and $b$.
It is also known as an unordered pair.
Also see
Sources
- Steven A. Gaal: Point Set Topology (1964)... (previous)... (next): Introduction to Set Theory: $1$. Elementary Operations on Sets
- Keith Devlin: The Joy of Sets: Fundamentals of Contemporary Set Theory (1993): $\S 1.3$
