Let $P = (\Omega, \mathcal{F}, \mathbb{P})$ be a D1159: Probability space such that

(i) | $E, F \in \mathcal{F}$ are each an D1716: Event in $P$ |

(ii) | $E \subseteq F$ is a D78: Subset of $F$ |

Then
\begin{equation}
\mathbb{P}(F \setminus E) = \mathbb{P}(F) - \mathbb{P}(E)
\end{equation}