1. Wedati, M., Sanuki, H., and Konno, K., ?Relationships Among Inverse Method, Bäcklund Transformations and Infinite Number of Conservation Laws?, Prog. Theoret. Phys. 53, 418?436 (1975).
2. Rogers, C. and Shadwick, W. R., Bäcklund Transformations and their Applications, Academic Press, New York, 1982.
3. Li, Y. S., ?Gauge Transformations, Bäcklund Transformation and Nonlinear Superposition Laws?, to appear in Adv. Math.
4. Tien, C., ?Bäcklund Transformation of Nonlinear Evolution Equations?, Acta Math. Appl. Sinica (1986).
5. Gu, C. H. and Hu, H. S., ?A Unified Explicit Form of Bäcklund Transformations for Generalized Hierarchies of KdV Equations?, Lett. Math. Phys. 11, 325?335 (1986).