1. [1] Y. C. Ma and M. J. Ablowitz, The periodic cubic Schrödinger equation, Stud. Appl. Math. 65 (1981), no. 2, 113–158.
2. [2] M. J. Ablowitz and H. Segur, Solitons and the inverse scattering transform, SIAM Studies in Applied Mathematics, vol. 4, Society for Industrial and Applied Mathematics (SIAM), Philadelphia, Pa., 1981.
3. [3] I. V. Čerednik, Differential equations for Baker-Ahiezer functions of algebraic curves, Funktsional. Anal. i Prilozhen. 12 (1978), no. 3, 45–54, 96.
4. [4] P. Deift, F. Lund, and E. Trubowitz, Nonlinear wave equations and constrained harmonic motion, Comm. Math. Phys. 74 (1980), no. 2, 141–188.
5. [5] R. L. Devaney, Transversal homoclinic orbits in an integrable system, Amer. J. Math. 100 (1978), no. 3, 631–642.