1. S. Weinberg:Proceedings of the 1970 Brandeis Summer Institute in Theoretical Physics, edited byS. Deser (Cambridge, 1970), p. 287.
2. D. V. Volkov:Particles and Nuclei,4, 3 (1973).
3. C. J. Isham, A. Salam andJ. Strathdee:Ann. of Phys.,62, 98 (1971).
4. V. I. Ogievetsky:Proceedings of the X Winter School on Theoretical Physics (Karpach, 1973).