# Particular Point Space is Scattered

## Theorem

Let $T = \struct {S, \tau_p}$ be a particular point space.

Then $T$ is scattered.

## Proof

Let $H \subseteq S$ such that $p \notin H$.

From Subset of Particular Point Space is either Open or Closed, $H$ is closed in $T$.

We have that Closed Set in Particular Point Space has no Limit Points.

So if $p \notin H$ then $H$ has no limit points.

So by definition, every element of such a set $H$ is an isolated point.

So if $p \notin H$ then $H$ is by definition not dense-in-itself.

Now let $H \subseteq S$ such that $p \in H$.

We have that $\set p \in \tau_p$.

That is, $p$ is an open point of $T$.

From Point in Topological Space is Open iff Isolated, $p$ is an isolated point.

So if $p \in H$ then $H$ is by definition not dense-in-itself.

Hence the result, by definition of a scattered space.

$\blacksquare$

## Sources

- 1978: Lynn Arthur Steen and J. Arthur Seebach, Jr.:
*Counterexamples in Topology*(2nd ed.) ... (previous) ... (next): Part $\text {II}$: Counterexamples: $8 \text { - } 10$. Particular Point Topology: $9$