1. An Invariant Volume-Mean-Value Property
2. E. Artin, The Gamma Function, Holt, Rinehart and Winston, 1964.
3. P. L. Duren, Univalent Functions, Springer-Verlag, 1983.
4. E. C. Titchmarsh, The Theory of Functions, 2nd ed., Oxford Univ. Press, 1939.