Let $X$ be a D11: Set.
Let $E_n$ be a D11: Set for each $n \in \mathbb{N}$ such that
Let $E_n$ be a D11: Set for each $n \in \mathbb{N}$ such that
(i) | $\bigcap_{n \in \mathbb{N}} E_n$ is the D76: Set intersection of $E = \{ E_n \}_{n \in \mathbb{N}}$ |
Then
\begin{equation}
X \subseteq \bigcap_{n \in \mathbb{N}} E_n
\quad \iff \quad \forall \, n \in \mathbb{N} : X \subseteq E_n
\end{equation}