ThmDex – An index of mathematical definitions, results, and conjectures.
Result R4161 on D76: Set intersection
Subset of countable intersection iff subset of every set in the intersection
Formulation 0
Let $X$ be a D11: Set.
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}