1. H. Harari:Proceedings of the IV International Symposium on Electron and Photon Interactions at High Energies (Liverpool, 1969).
2. A. Dar:Proceedings of the V Rencontre de Moriond sur les interactions électromagnétiques (Méribel, 1970).
3. M. Ross, F. S. Henyey andG. L. Kane:Nucl. Phys.,23 B, 269 (1970).
4. J. Tran Thanh Van:Decisive tests for dip mechanisms (to be published inPhys. Rev. D).
5. Ling Lie Wang:Phys. Rev. Lett.,16, 756 (1966).