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