1. Aggarval:Notes on Nonlinear Systems (New York, N. Y., 1972).
2. G. Nicolis andI. Prigogine:Self-Organization in Nonequilibrium Systems (New York, N. Y., 1977), and the numerous references contained there.
3. W. Steeb:Lett. J. Phys. A, in press, and the references therein (1977).
4. L. Meirovitch:Methods of Analytical Dynamics (New York, N. Y., 1970), p. 205.
5. C. Olech:Ann. Inst. Fourier,14, 87 (1964).