Suppose that $f$ is entire and that for each $z$, either $|f(z)| \le 1$ or $|f'(z)| \le 1$. How can I prove that $f$ is a linear polynomial?
Suppose that $ f $ is entire and that for each $ z $, either $ |f(z)| \leq 1 $ or $ |f^\prime (z) |\leq 1 $. Prove that $ f $ is a linear polynomial.