T4 Space is Preserved under Homeomorphism

Theorem
Let $T_A = \left({X_A, \vartheta_A}\right), T_B = \left({X_B, \vartheta_B}\right)$ be topological spaces.

Let $\phi: T_A \to T_B$ be a homeomorphism.

If $T_A$ is a $T_4$ space, then so is $T_B$.

Proof
We have that $\left({X, \vartheta}\right)$ is a $T_4$ space iff:


 * $\left({X, \vartheta}\right)$ is a normal space
 * $\left({X, \vartheta}\right)$ is a Fréchet ($T_1$) space.

From Normal Space is Preserved under Homeomorphism:
 * If $T_A$ is a normal space, then so is $T_B$.

From $T_1$ (Fréchet) Space is Preserved under Homeomorphism:
 * If $T_A$ is a $T_1$ (Fréchet) space, then so is $T_B$.

Hence the result.