Discrete Space is First-Countable

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Theorem

Let $T = \left({S, \tau}\right)$ be a discrete topological space.


Then $T$ is first-countable.


Proof

From Point in Discrete Space is Neighborhood, every point $x \in S$ is contained in an open set $\left\{{x}\right\}$.

From the definition of local basis, it is clear that $\left\{{\left\{{x}\right\}}\right\}$ is (trivially) a local basis at $x$.

That is, that every open set of $S$ containing $x$ also contains at least one of the sets of $\left\{{\left\{{x}\right\}}\right\}$.

Equally trivially, we have that $\left\{{\left\{{x}\right\}}\right\}$ is countable.

Hence the result by definition of first-countable.

$\blacksquare$


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