1. G. N. Watson, A Treatise on the Theory of Bessel Functions, 2nd ed., Cambridge University Press, London, 1952, Chap. 4.
2. G. Birkhoff and G.C. Rota, Ordinary Differential Equations, 2nd ed., Wiley, New York, 1969.
3. G. M. Murphy, Ordinary Differential Equations and Their Solutions, D. Van Nostrand, New York, 1960.
4. Zur Aufllösung linearer homogener Differentialgleichungen 2. Ordnung