1. M. Gell-Mann:Phys. Lett.,8, 214 (1964);G. Zweig: CERN preprint 8419/TH Feb. 1964, unpublished.
2. For a review, seeR. H. Dalitz:Quark Model jor the Elementary Particles, Les Houches lecture notes (1965);H. J. Lipkin:Proc. of the Yalta Internat. School 1966. AlsoL. Van Hove: lectures at1966 Scottish Universities' Summer School in Physics, CERN preprint, June 1966;J. J. J. Kokkedee andL. Van Hove:Nuovo Cimento,42 A, 711 (1966).
3. W. Thirring: inLectures on Theoretical Physics (vienna, 1963), p. 450.
4. R. Delbourgo, M. A. Rushid, A. Salam andJ. Strathdee: inHigh-Energy Physics and Elementary Particles (Vienna, 1965), p. 455.
5. G. Morpurgo:Physics,2, 95 (1965);O. W. Greenberg:Phys. Rev.,147, 1077 (1966).