Real meromorphic functions and a result of Hinkkanen and Rossi
Real meromorphic functions and a result of Hinkkanen and Rossi
Let $f$ be a transcendental meromorphic function such that all but finitely many of the poles of $f$ and zeroes of $f'$ are real. Generalising a result of Hinkkanen and Rossi (Proc. Amer. Math. Soc. 92 (1984) 72–74), we characterize those $f$ such that $f'$ takes some nonzero value only …