I don't see anywhere in the hypotheses that says fisinvertible so you should not be writing " ". Write, rather, "if then there exist x in such that f(x)= y. Since , either or .

Case 1: if then .

Case 2: if then .

So your friend was essentially telling you the same thing I just did!.

and so .

A friend of mine pointed out that I could show this in the following manner:

If then there exist x in such that f(x)= E. Since , then so and so . Therefore ..

Then

I do not know how to continue. If , what then? Should I be doing all of this differently?

Thank you.