WIithout $\phi$ , How can a subset form a open base for any topology?
The empty union, $\bigcup \emptyset$, i.e., the union of no elements of the basis at all, is $\emptyset$.
WIithout $\phi$ , How can a subset form a open base for any topology?
The empty union, $\bigcup \emptyset$, i.e., the union of no elements of the basis at all, is $\emptyset$.