$\tau=\mathcal{C}(X,\tau);F\in\mathcal{C}(X,\tau)$ ve $x\notin F \text{olsun.}$
$(F\in\mathcal{C}(X,\tau))(x\notin F)\Rightarrow\left.\begin{array}{rr} (F\in\mathcal{C}(X,\tau))(x\in\setminus F) \\ F\in\mathcal{C}(X,\tau)\Rightarrow\setminus F\in\tau\end{array}\right\}\Rightarrow$
$\Rightarrow\left.\begin{array}{rr} (F\in\mathcal{C}(X,\tau))(x\in\setminus F\in\tau) \\ \tau=\mathcal{C}(X,\tau)\end{array}\right\}\Rightarrow (U:=F\in\tau) (V:=\setminus F\in\tau)$
$\Rightarrow (U\in\mathcal{U}(F)) (V\in\mathcal{U}(x)) (U\cap V=\emptyset)$