Symmetric Difference of Unions

Theorem
Let $R$, $S$ and $T$ be sets.

Then:
 * $\paren {R \cup T} * \paren {S \cup T} = \paren {R * S} \setminus T$

where:
 * $*$ denotes the symmetric difference
 * $\setminus$ denotes set difference
 * $\cup$ denotes set union