Associative Law of Multiplication

Theorem
Let $\mathbb F$ be one of the standard number sets: $\N, \Z, \Q, \R$ and $\C$.

Then:
 * $\forall x, y, z \in \mathbb F: x \times \paren {y \times z} = \paren {x \times y} \times z$

That is, the operation of multiplication on the standard number sets is associative.