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) | \begin{equation} \mathbb{P}(E) = 1 \end{equation} |

Then
\begin{equation}
\mathbb{P}(E \cup F)
= 1
\end{equation}