1. See e.g. Close, F.E.: An introduction to quarks and partons, Chap. 6. New York: Academic Press 1979
2. Green, A.M., Niskanen, J.A.: Nucl. Phys. A412, 448 (1984)
3. For a review, see Green, A.M., Niskanen, J.A.: In: Progress in particle and nuclear physics. Faessler, A. (ed.) Vol. 18, p. 93. New York: Pergamon 1987
4. Furui, S., Faessler, A.: Nucl. Phys. A424, 525 (1984)
5. Isgur, N., Paton, J.E.: Phys. Lett.124B, 247 (1983); Phys. Rev. D31, 2910 (1985)