If f is a function from A to B, then F is into function if _____?

If f is a function from A to B, then F is into function if _____?

Explanation

A function f: A → B is into if it doesn't cover the entire codomain B, meaning there are elements in B that aren't mapped to by any element in A. 

This happens when the range of f (the set of elements in B that are actually mapped to) is a proper subset of B.

Therefore, f is into if Range f ≠ B.