1. A. Newell:Near integrable systems, nonlinear tunnelling and solutions in slowly changing media, inNonlinear Evaluation Equations Solvable by the Spectral Transform, edited byF. Calogero (London, 1978);F. Calogero andA. Degasperis: preprint, No. 66 (1978), Istituto di Fisica del-l'Università, Roma, submitted toLett. Nuovo Cimento.
2. F. Calogero andA. Degasperis: preprint, No. 73 (1978), Istituto di Fisica dell'Università, Roma, submitted toLett. Nuovo Cimento.
3. M. J. Ablowitz:SIAM Rev.,19, 663 (1977);M. J. Ablowitz andJ. F. Ladik:Studies in Appl. Math.,55, 213 (1976).
4. K. M. Case:Journ. Math. Phys.,14, 916 (1973);K. M. Case andM. Kac:Journ. Math. Phys.,14, 594 (1973).
5. H. S. Carslaw:Theory of Fourier Series and Integrals (New York, N. Y., 1930).