I'm asking this question on regards to an assignment my teacher handed out and she has a nasty habbit of never replying to e-mails. The question is already answered but it only brings up more questions than it answers.

She wrote down the answer to this was False $f(2) = f(-2)$ but if the condition was that it was an integer implies an integer, how would it not be an onto? The answer it gives is always going to be an integer

It could just be that I don't understand the question but is it because that it wasn't 
positive integers imply positive integers? ($\Bbb Z^+ \to\Bbb Z^+$).

Thanks