Let $M = (X, \mathcal{F}, \mu)$ be a D1158: Measure space such that

(i)	$E, F_1, \ldots, F_N \in \mathcal{F}$ are each a D1109: Measurable set in $M$
(ii)	$F_1, \ldots, F_N$ is a D5143: Set partition of $X$

Then \begin{equation} \mu(E) = \sum_{n = 1}^N \mu(E \cap F_n) \end{equation}