User:Dfeuer/Definition:Singleton

Definition
Let $x$ be a set.

Then the unique class $S$ such that


 * $\forall y: y \in S \iff y = x$

is called singleton $x$ and is written $\{ x \}$.

Also see

 * User:Dfeuer/Set has Unique Singleton
 * User:Dfeuer/Singleton Set is Set