Particular Point Space is Scattered

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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.

$\blacksquare$


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