Base for a topology

Set

context $\langle X,T\rangle$ … topological space
definiendum $B\in$ it
inclusion $B\subseteq T$
for all $U\in T$
exists $C\subseteq B$
postulate $U=\bigcup C$

Discussion

A base $B$ for a topology is a collection its open sets, which suffice to cover any open set.

Parents

Context

Topological space