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71(1951), 70–101.
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3. Leonard E. Dickson, Studies in the Theory of Numbers,Chapter 13, University of Chicago Press, Chicago, 1930.
4. Marvin I. Knopp, Modular Functions in Analytic Number Theory, 2nd ed., Chelsea Publishing Co., New York, 1993.
5. Joseph Lehner, A Short Course in Automorphic Functions,Holt, Rinehart and Winston, New York, 1966.