[0KK]↺↻
For example, if \(X\) is a metric space, then the family of all open balls is a base.
[0KM]↺↻
[0KQ]↺↻
[0KS]↺↻
[0M7]↺↻
[0KV]↺↻
[0KX]↺↻
[0KZ]↺↻
[0M1]↺↻
[0M3]↺↻
[0M5]↺↻
[2F7]↺↻
[0M9]↺↻
[2F5]↺↻
[2FD]↺↻
[2F9]↺↻