1. A. Martin:Lecture given at IX Internationale Universitätswochen für Kernphysik, Schladming, 1970 (Lecture notes).
2. L. Łukaszuk andA. Martin.Nuovo Cimento,52 A, 122 (1967).
3. B. Bonnier andR. Vinh Mau:Phys. Rev.,165, 1323 (1967); cf.Phys. Lett.,24 B, 477 (1967).
4. R. Wit: CERN preprint TH. 1182 (to be published inNucl. Phys.).
5. A. Martin:Nuovo Cimento,47 A, 265 (1967);A. K. Common:Nuovo Cimento,63 A, 863 (1969);F. J. Yndurain:Nuovo Cimento,64 A, 225 (1969).