1. A. S. Wightman; see also the conclusion, at p. 162, to the talk byD. Zwanziger; inInvariant Wave Equations, Proceedings of the Ettore Majorana International School of Mathematical Physics of Erice, July 1977 (New York, N. Y., 1978).
2. G. Labonté:Nuovo Cimento A,75, 69 (1983).
3. G. Labonté:Nuovo Cimento A,75, 416 (1983).
4. G. Labonté:Nuovo Cimento A,72, 173 (1982).
5. G. Velo andD. Zwanziger:Phys. Rev.,188, 2218 (1969).