1. H. Harari:Proceedings of the International Conference on Duality and Symmetry in Hadron Physics, edited byE. Gotsman (Tel Aviv, 1971), p. 148;Shu-Yuan Chu andA. W. Hendry:Phys. Rev. Lett.,25, 313 (1970).
2. M. Imachi, T. Oroguchi, S. Otsuki andF. Toyoda:Progr. Theor. Phys.,45, 1849 (1971).
3. B. Schrempp andF. Schrempp: DESY 72/45, 72/46 (1972).
4. N. W. Dean:Nuovo Cimento,52 A, 1129 (1967).
5. R. Blankenbecler andM. L. Goldberger:Phys. Rev.,126, 766 (1962).