Definition:Normal Space

Definition
Let $T = \struct {S, \tau}$ be a topological space.

$\struct {S, \tau}$ is a normal space :
 * $\struct {S, \tau}$ is a $T_4$ space
 * $\struct {S, \tau}$ is a $T_1$ (Fréchet) space.

That is:
 * $\forall A, B \in \map \complement \tau, A \cap B = \O: \exists U, V \in \tau: A \subseteq U, B \subseteq V, U \cap V = \O$


 * $\forall x, y \in S$, both:
 * $\exists U \in \tau: x \in U, y \notin U$
 * $\exists V \in \tau: y \in V, x \notin V$

This space is also referred to as normal Hausdorff.