# Discrete Topology is Topology

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## Theorem

Let $S$ be a set.

Let $\tau$ be the discrete topology on $S$.

- $\tau$ is a topology on $S$.

## Proof

Let $T = \struct {S, \tau}$ be the discrete space on $S$.

Then by definition $\tau = \powerset S$, that is, is the power set of $S$.

We confirm the criteria for $T$ to be a topology:

- $(1): \quad$ By definition of power set, $\O \in \powerset S$ and $S \in \powerset S$.
- $(2): \quad$ From Power Set with Union is Monoid, $\powerset S$ is closed under set union.
- $(3): \quad$ From Power Set with Intersection is Monoid, $\powerset S$ is closed under set intersection.

$\blacksquare$

## Sources

- 1978: Lynn Arthur Steen and J. Arthur Seebach, Jr.:
*Counterexamples in Topology*(2nd ed.) ... (previous) ... (next): Part $\text {II}$: Counterexamples: $1 \text { - } 3$. Discrete Topology