Metric Space is Perfectly Normal

Theorem
Let $M = \struct {A, d}$ be a metric space.

Then $M$ is a perfectly normal space.

Proof
By definition, a topological space is perfectly normal space it is:
 * a perfectly $T_4$ space
 * a $T_1$ (Fréchet) space.

We have that:
 * a Metric Space is Perfectly $T_4$
 * a Metric Space is $T_2$ (Hausdorff)
 * a $T_2$ (Hausdorff) Space is a $T_1$ (Fréchet) Space.