Let $X$ be a D11: Set such that
(i) | $E_j \subseteq X$ is a D78: Subset of $X$ for each $j \in J$ |
Then
\begin{equation}
\bigcup_{j \in J} E_j
\subseteq X
\end{equation}
(i) | $E_j \subseteq X$ is a D78: Subset of $X$ for each $j \in J$ |