Let $X$ be a D11: Set.
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

(1)	\begin{equation} \forall \, i \in J : E_i \subseteq \bigcup_{j \in J} E_j \end{equation}
(2)	\begin{equation} \forall \, j \in J : E_j \subseteq X \quad \implies \quad \bigcup_{j \in J} E_j \subseteq X \end{equation}