Let $X$ be a D11: Set.
Let $E_j$ be a D11: Set for each $j \in J$ such that
Let $E_j$ be a D11: Set for each $j \in J$ such that
(i) | $\bigcup_{j \in J} E_j$ is the D77: Set union of $E = \{ E_j \}_{j \in J}$ |
Then
\begin{equation}
\bigcup_{j \in J} E_j
\subseteq X
\quad \iff \quad \forall \, j \in J : E_j \subseteq X
\end{equation}