1. G. Springer, Introduction to Riemann Surfaces, Addison-Wesley, Reading, Mass. (1957).
2. V. I. Arnol'd, Supplementary Chapters of the Theory of Ordinary Differential Equations [in Russian], Nauka, Moscow (1978).
3. V. I. Arnol'd, Ordinary Differential Equations [in Russian], Nauka, Moscow (1971).
4. V. I. Arnol'd and A. L. Krylov, "Uniform distribution of points on the sphere, and some ergodic properties of the solutions to ordinary differential equations in the complex domain," Dokl. Akad. Nauk SSSR,148, No. 1, 9?12 (1963).
5. A. Poincaré, Les Méthodes Nouvelles de la Mécanique Celeste, Vols. 1, 2, 3. Gauthier-Villars, Paris (1892); reprint, Dover, New York (1957).