1. A. V. Barnes, D. J. Mellema, A. V. Tollestrup, R. L. Walker, O. L. Dahl, R. A. Johnson, R. W. Kenney andM. Pripstein: California Institute of Technology preprint (1974).
2. W. F. Baker, A. S. Carroll, I-H. Chiang, R. L. Cool, D. P. Eartly, O. Fackler, G. Giacomelli, P. F. M. Koehler, T. F. Kycia, K. K. Li, P. O. Mazur, P. Mockett, K. P. Pretzi, D. C. Rahm, R. Rubinstein andA. A. Wehmann: NAL-Pub-74/76-EXP preprint (July 1974).
3. V. Barger andR. J. N. Phillips:Phys. Rev.,187, 2210 (1969);E. Leader andB. Nicolescu:Phys. Rev. D,7, 836 (1973).
4. G. Girardi, R. Lacaze, R. Peschanski, G. Cohen-Tannoudji, F. Hayot andH. Navelet:Nucl. Phys.,47 B, 445 (1972); see alsoR. J. N. Phillips: talk at theAmsterdam Conference on Elementary Particles, Proceedings (Amsterdam, 1972), p. 111 and references quoted therein.
5. V. Barger: talk at theXVII International Conference on High-Energy Physics, London (July 1974), University of Wisconsin preprint (1974).