1. Louis de Branges and James Rovnyak, Square Summable Power Series, Holt, Rinehart and Winston, New York, 1966.
2. Nathan Jacobson, Lectures in Abstract Algebra, vol. 1, Van Nostrand, Princeton, N. J., 1951, p. 19.
3. Ivan Niven and H. S. Zuckerman, An Introduction to the Theory of Numbers, 2nd ed., Wiley, New York, 1966.
4. John Riordan, Combinatorial Identities, Wiley, New York, 1968.