1. R. Bullow,Solitons (M. Lokshmanan, ed.), New York: Springer-Verlag (1987).
2. Handbook of Mathematical Functions (M. Abramowitz and I. Stegun, eds), New York: Dover Publications, Inc. (1965).
3. For example, S. Novikov, V. Manakov, L. Pitaevskii, and V. Zakharov,Theory of Solitons, New York: Plenum (1984).
4. SeePhysics and Mathematics of Strings (dedicated to the memory of V. Knizhnik) (Brink, Polyakov, and Friedan, eds.), Singapore: World Scientific (1990).Steklov Mathematical Institute