In a normal (T4) space, disjoint closed sets A, B admit a continuous function f : X → [0,1] with f≡0 on A and f≡1 on B. Root of metrisation and Tietze extension theorems.
In a normal (T4) space, disjoint closed sets A, B admit a continuous function f : X → [0,1] with f≡0 on A and f≡1 on B. Root of metrisation and Tietze extension theorems.