1. M.E. Mayer, in Proc. of the Workshop on Gauge Theories, Mexico City, 1980, Hadronic J. 4 (1981) 108–152.
2. L. O’Raifeartaigh, Hidden Gauge Symmetry, Rep. Prog. Phys. 42 (1979) 159–223.
3. L. Michel and L. Radicati, Ann. Phys. NY 66 (1971) 758
4. L. Michel and L. Radicati, Ann. Inst. H. Poincare 18 (1973) 185, and further references there.
5. E Witten, Search for a Realistic Kaluza-Klein Theory, Princeton Preprint, 1981.