Definition:Filter Basis

Definition
Let $X$ be a set, and $\mathcal P \left({X}\right)$ be the power set of $X$.

Let $\mathcal B \subset \mathcal P \left({X}\right)$.

Then $\mathcal F := \left\{{V \subseteq X: \exists U \in \mathcal B: U \subseteq V}\right\}$ is a filter on $X$ iff the following conditions hold:
 * $(1) \quad \forall V_1, V_2 \in \mathcal B: \exists U \in \mathcal B: U \subseteq V_1 \cap V_2$
 * $(2) \quad \varnothing \not \in \mathcal B, \mathcal B \ne \varnothing$

Any such $\mathcal B$ is called a filter basis (plural: filter bases).

$\mathcal F$ is said to be generated by $\mathcal B$ or spanned by $\mathcal B$.

This is proved in Filter Basis Generates Filter.

Equivalent Filter Bases
Two filter bases are equivalent iff they both generate the same filter.

Also see

 * Basis (Topology)


 * Filter Sub-Basis