Relative Complement of Cartesian Product

Theorem
Let $A$ and $B$ be sets.

Let $X \subseteq A$ and $Y \subseteq B$.

Then:
 * $\relcomp {A \mathop \times B} {X \times Y} = \paren {A \times \relcomp B Y} \cup \paren {\relcomp A X \times B}$