Definition:Closed Element

Definition

Let $\struct {S, \preceq}$ be an ordered set.

Let $\cl$ be a closure operator on $S$.

Let $x \in S$.

Definition 1

The element $x$ is a closed element of $S$ (with respect to $\cl$) if and only if $x$ is a fixed point of $\cl$:

$\map \cl x = x$

Definition 2

The element $x$ is a closed element of $S$ (with respect to $\cl$) if and only if $x$ is in the image of $\cl$:

$x \in \Img \cl$

Also see

• Equivalence of Definitions of Closed Element
• Definition:Closure of Element under Closure Operator

• Results about closed elements can be found here.

Special case

• Definition:Closed Set under Closure Operator