1. See, for example, the review byV. Silvestrini: inProceedings of the XVI International Conference on High-Energy Physics, Vol.4 (Chicago, Ill., 1972), p. 1.
2. P. Shepard:Bull. Amer. Phys. Soc.,17, 435 (1972).
3. I. B. Khriplovich: inProceedings of the XVI International, Conference on High-Energy Physics (Chicago, Ill., 1972);D. A. Dicus:Phys. Rev. D,8, 890 (1973).
4. R. W. Brown, V. K. Cung, K. O. Mikaelian andE. A. Paschos:Phys. Lett.,43 B, 403 (1973).
5. A. I. Nikishiv:Žurn. Ėksp. Teor. Fiz.,39, 757 (1960) (English translation:Sov. Phys. JETP,12, 529 (1961));G. Furlan, R. Gatto andC. Longhi:Phys. Lett.,12, 262 (1964).