1. P. G. O. Freund:Phys. Rev. Lett.,14, 1088;15, E 176 (1965). This paper will be referred to hereafter as I.
2. N. N. Bogoliubov, V. Matveev, N. van Hieu, D. Stoianov, B. Struminsky, A. Tavkhelidze andV. Shelest: Dubna preprints D-2075 and P-2141.
3. R. S. Feynman:Proceedings of the Aix-en-Provence Conf. on Elementary Particles vol.2 (Saclay, 1961), p. 207. I wish to thankJ. J. Sakurai for calling my attention to this reference.
4. Infinite-dimensional unitary representations for the groupM 12 have been constructed inP. G. O. Freund:Phys. Rev. Lett.,14, 803 (1965). See also the more recent work ofY. Dothan, M. Gell-Mann andY. Ne’eman: Caltech preprint.