1. For a review see, for instance,R. H. Dalitz: inProceedings of the XIII International Conference on High-Energy Physics (Berkeley, Cal., 1967).
2. L. C. Biedenharn, M. Y. Han andH. Van Dam: to be published.
3. L. P. Staunton: to be published.
4. P. A. M. Dirac:Proc. Roy. Soc., A322, 435 (1971); A328, 1 (1972).
5. P. A. M. Dirac:Journ. Math. Phys.,4, 901 (1963).