$\textbf{$T_4$ space / normal Hausdorff space}$
A $T_2$ space $X$ is called a $T_4$ space or normal Hausdorff space if for any two disjoint closed sets $F$ and $G$ there are disjoint open sets $U$ and $V$ with $F\subset U$ and $G\subset V$.
Note: The condition $T_2$ can be equivalently changed to $T_1$.
$\textbf{$T_4$ space / normal Hausdorff space}$
A $T_2$ space $X$ is called a $T_4$ space or normal Hausdorff space if for any two disjoint closed sets $F$ and $G$ there are disjoint open sets $U$ and $V$ with $F\subset U$ and $G\subset V$.
Note: The condition $T_2$ can be equivalently changed to $T_1$.
copied
๐โย ๐ฌ๐ฉ๐๐๐ย /ย ๐ง๐จ๐ซ๐ฆ๐๐ฅย ๐๐๐ฎ๐ฌ๐๐จ๐ซ๐๐ย ๐ฌ๐ฉ๐๐๐
A ๐โ space ๐ is called a ๐โ space or normal Hausdorff space if for any two disjoint closed sets ๐น and ๐บ there are disjoint open sets ๐ and ๐ with ๐นโ๐ and ๐บโ๐.
Note: The condition ๐โ can be equivalently changed to ๐โ.