Proof That Any Two Points of a T1 Space Are in Open Sets Not Containing the Other Point
If a topological spaceis a T1 space then for any pair of distinct pointsopen setsexist with
Supposeis a T1 space. For anyis closed. Letbe distinct points ofandare closed soandare open.
Conversely supposeis open. Letthenand an open setexists such thatHenceand
Since allare openis open andis closed so