1. For reviews and more complete references, see Refs. 10 and 11.
2. E. K. Sklyanin and L. D. Faddeev, Dokl. Akad. Nauk SSSR 243, 1430 (1978) [Sov. Phys.-Dokl. 23, 902].
3. E. K. Sklyanin, Izv. Akad. Nauk SSSR 244, 1337 (1979) [Sov. Phys.Dokl. 24, 107 (1979)].
4. H. B. Thacker and D. Wilkinson, Phys. Rev. D19, 3660 (1979).
5. J. Honerkamp, P. Weber, and A. Wiesler, Nucl. Phys. B152, 266 (1979).