1. R. Rossmanith, this conference
2. for reviews see V.N. Baier, Proc. Intl. School of Physics “Enrico Fermi”, Varenna, 1969, Course XLVI (Academic Press, 1972), p. 1–49
3. J.D. Jackson, Rev. Mod. Phys. 48 (1976) 417
4. for recent reviews see J. Buon, this conference, A.W. Chao, this conference
5. D. Potaux, Proc. 8th Intl. Conf. High-Energy Accelerators, CERN 1971, ed. M.H. Blewett, p. 127