Some remarks on Schottky's theorem
Walter Kurt Hayman · Mathematical Proceedings of the Cambridge Philosophical Society · 1947
1. We denote by the class of all functions regular in |z| < 1, and never taking the values 0 or 1 in |z| < 1. Then Schottky's(1) theorem states: Theorem A. Let f(z) = a0 + a1z + … belong to . Then and hence where and the constantsK(a0), K(a0,ρ) depend only on the quantities indicated.