1. Sasaki, R., Nucl. Phys. B154, 343 (1979).
2. Zakharov, V.E., and Shabat, A.B., JETP (Sov. Phys.) 34, 62 (1972).
3. Ablowitz, M.J., Kaup, D.K., Newell, A.C., and Segur, H., Phys. Rev. Lett. 31, 125 (1973).
4. Sasaki, R., ?Geometric Approach to Soliton Equations?, (preprint) Niels Bohr Institute, Sept. 79. This paper also contains references to the prior work of Hermann, Corones, and Crampin on the SL(2, IR) structure in this context.
5. Temple, G., Lectures on Topics in Nonlinear Differential Equations, pp. 1?15, Rept. 1415, David Taylor Model Basin, Carderock, Md., 1960.