Thread: Empty Set as a union of Basis Elements

I just had a quick question.

If is a basis for a topology on a set defined in the way

1)
2) If and , then there exists such that

Then it is a fact that this generates a topology on , where the sets in the topology are unions of elements of . But we require to be an element in this topology - is it ok to take a union of none of the basis elements?

Thanks for any help.

By definition .