References
Abramowitz, M. and Stegun, C. A. (Eds.). ``Riemann's Differential Equation.'' §15.6 in
Handbook of Mathematical Functions with Formulas, Graphs, and Mathematical Tables, 9th printing.
New York: Dover, pp. 564-565, 1972.
Morse, P. M. and Feshbach, H. Methods of Theoretical Physics, Part I. New York: McGraw-Hill, pp. 541-543, 1953.