Functions & Open Sets in a Topology – Lecture 5 (Topology)

When we write f : X → Y, what exactly is being claimed about the function f?

1. A.Every element of Y is f(x) for some x in X
2. B.f maps every element of X to some element of Y
3. C.f is one-to-one but not necessarily onto Y
4. D.X and Y must have the same cardinality