1. J. Mathews, R.L. Walker, Mathematical Methods of Physics (Benjamin, Menlo Park, 1970), Chap. 12-2
2. Private communication by Klaus Eidmann
3. M. Abramowitz, I.A. Stegun, Handbook of Mathematical Functions (Dover Publ. Inc., New York, 1970), Chap. 20
4. V.I. Arnold, Mathematical Methods of Classical Mechanics (Springer, New York, 1978), p. 297
5. V.I. Arnold, Dynamical systems, vol. 3 (Springer, New York, 1988), pp. 200–211