===== Base for a topology =====
==== Set ====
| @#55CCEE: context     | @#55CCEE: $\langle X,T\rangle$ ... topological space |
| @#FFBB00: definiendum | @#FFBB00: $B\in$ it |
| @#AAFFAA: inclusion   | @#AAFFAA: $B\subseteq T$ |
| @#FFFDDD: for all     | @#FFFDDD: $U\in T$ |
| @#FFFDDD: exists      | @#FFFDDD: $C\subseteq B$ |
| @#55EE55: postulate   | @#55EE55: $U=\bigcup C$ |

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

==== Parents ====
=== Context ===
[[Topological space]]