1. E. Eberle:Lett. Nuovo Cimento,1, 68 (1971).
2. J. Wess:Nuovo Cimento,14, 527 (1959).
3. See for instance:R. E. Marshak, Riazuddin andC. P. Ryan:Theory of Weak Interactions in Particle Physics (New York, 1969).
4. C. Mistretta, D. Imrie, J. A. Appel, R. Budnitz, L. Carroll, M. Goitein, K. Hanson andR. Wilson:Phys. Rev. Lett.,20, 1523 (1968).
5. See for instance:K. Winter: in theAmsterdam International Conference on Elementary Particles, edited byA. G. Tanner andM. J. G. Veltman (Amsterdam, 1971), p. 333.