1. See, for example,B. Zumino:Proceedings of the XVII International Conference on High-Energy Physics, edited byJ. R. Smith (Chilton, Didcot, 1974), p. 254.
2. A. Salam andJ. Strathdee:Phys. Rev. D,11, 521 (1975).
3. L. Corwin, Y. Ne’eman andS. Sternberg:Rev. Mod. Phys.,47, 573 (1975).
4. S. Ferrara:Riv. Nuovo Cimento,6, 105, (1976);P. Fayet andS. Ferrara:Phys. Rep.,32 C, 249 (1977).
5. For a previous exposition of the theory for physicists, seeB. S. DeWitt:Relativity groups and topology, inProceedings of the Les Houches 1963 Seminar, edited byC. DeWitt andB. DeWitt (New York, N. Y., 1964).