Union with Relative Complement

Theorem
The union of a set $$T$$ and its relative complement in $$S$$ is the set $$S$$:


 * $$\complement_S \left({T}\right) \cup T = S$$

Proof
$$ $$

From the definition of relative complement, we have that $$T \subseteq S$$.

From Union with Superset is Superset‎, we have that $$T \subseteq S \iff S \cup T = S$$, from which the result follows.