Measure of Set Difference with Subset

Theorem
Let $\left({X, \Sigma, \mu}\right)$ be a measure space.

Let $S, T \in \Sigma$ be such that $S \subseteq T$, and suppose that $\mu \left({S}\right) < +\infty$.

Then:


 * $\mu \left({T \setminus S}\right) = \mu \left({T}\right) - \mu \left({S}\right)$

where $T \setminus S$ denotes set difference.