ThmDex – An index of mathematical definitions, results, and conjectures.
Result R4149 on D76: Set intersection
Countable intersection is a lower bound to each set in the intersection
Formulation 0
Let $E_n$ be a D11: Set for each $n \in \mathbb{N}$ such that
(i) $\bigcap_{n \in \mathbb{N}} E_n$ is a D76: Set intersection for $\{ E_n \}_{n \in \mathbb{N}}$
Then \begin{equation} \forall \, k \in \mathbb{N} : \bigcap_{n \in \mathbb{N}} E_n \subseteq E_k \end{equation}
Formulation 1
Let $E_n$ be a D11: Set for each $n \in \mathbb{N}$ such that
(i) $\bigcap_{n \in \mathbb{N}} E_n$ is a D76: Set intersection for $\{ E_n \}_{n \in \mathbb{N}}$
Then \begin{equation} \bigcap_{n \in \mathbb{N}} E_n \subseteq E_1, \quad \bigcap_{n \in \mathbb{N}} E_n \subseteq E_2, \quad \bigcap_{n \in \mathbb{N}} E_n \subseteq E_3, \quad \ldots \end{equation}
Proofs
Proof 0
Let $E_n$ be a D11: Set for each $n \in \mathbb{N}$ such that
(i) $\bigcap_{n \in \mathbb{N}} E_n$ is a D76: Set intersection for $\{ E_n \}_{n \in \mathbb{N}}$
This result is a particular case of R4148: Intersection is a lower bound to each set in the intersection. $\square$