# Definition:Separation (Topology)

## Definition

Let $T = \struct {S, \tau}$ be a topological space.

Let $A$ and $B$ be open sets of $T$.

$A$ and $B$ form a separation of $T$ if and only if:

$(1): \quad A$ and $B$ are non-empty
$(2): \quad A \cup B = S$
$(3): \quad A \cap B = \O$

That is, if and only if $A$ and $B$ form a partition of the set $S$.

Such a separation can be denoted:

$A \mid B$

$A$ and $B$ are said to separate $T$.

## Also known as

A separation in this particular context is also known as a partition.

However, because the latter term has a definition in set theory, separation is preferred so as to reduce ambiguity and the possibility of confusion.

## Also see

• Results about separations can be found here.