Basis for Topology

Statements

Definition. A basis for the topology $\tau$ of a topological space $(X,\tau )$ is a family $\mathcal{B}\subseteq \tau$ of open sets such that every open set of the topology can be represented as the union of some subfamily of $\mathcal{B}$.

References

https://en.wikipedia.org/wiki/Base_(topology)

@Tu11 Definition A.6