Square of Cube Number is Cube/Proof 2

Theorem
Let $a \in \N$ be a natural number.

Let $a$ be a cube number.

Then $a^2$ is also a cube number.

Proof
From Cube Number multiplied by Cube Number is Cube, if $a$ and $b$ are cube numbers then $a b$ is a cube number.

The result follows by setting $b = a$.