1. K. Fujiwara andT. Kitazoe: Kobe University, Physics Department, preprint, November 1969.
2. A. Giovannini andE. Predazzi:Nuovo Cimento,52 A, 255 (1967).
3. E. Fermi:Progr. Theor. Phys.,5, 570 (1950);Phys. Rev.,81, 683 (1951).
4. A. Giovannini andE. Predazzi: inProceedings of the Topical Conference on High-Energy Collisions of Hadrons, Vol.2 (CERN, 1968), p. 102.
5. I should thank Prof. K.Sitte for a useful discussion on this point.