1. S. D. Drell, H. J. Lipkin andA. de Shalit: unpublished;
2. M. Jean:Atti del L Congressu della S.I.F. (Bari, 1963) (to be published inSuppl. Nuovo Cimento);T. Ericson:Intern. Conf. on High-Energy Physics and Nuclear Structure (CERN, 1963) (p. 68, CERN 63, 28 July 1963).
3. L. Gilly, M. Jean, R. Meunier, M. Spighel, J. P. Steoot, P. Duteil andA. Rode:Phys. Lett.,11, 244 (1964).
4. G. F. Chew, M. L. Goldberger, F. E. Low andY. Nambu:Phvs. Rev.,106, 1337 (1957).
5. G. F. Chew andF. E. Low:Phys. Rev.,101, 1571 (1956).