Cardinality of Cartesian Product of Finite Sets/General Result

Theorem
Let $\displaystyle \prod_{k \mathop = 1}^n S_k$ be the cartesian product of a sequence of sets $\left \langle {S_n} \right \rangle$.

Then:
 * $\left|{\displaystyle \prod_{k \mathop = 1}^n S_k}\right| = \displaystyle \prod_{k \mathop = 1}^n \left|{S_k}\right|$

This can also be written:
 * $\left|{S_1 \times S_2 \times \ldots \times S_n}\right| = \left|{S_1}\right| \times \left|{S_2}\right| \times \ldots \times \left|{S_n}\right|$