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

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

Then
\begin{equation}
\mathbb{P}(\Omega \setminus E) = 1 - \mathbb{P}(E)
\end{equation}