1. M. Giffon, J. Joseph andJ. Meyer:Nuovo Cimento,5 A, 478 (1971).
2. B. Amblard: Thesis of Paris University, No. CNRS A.0.5421 (March 1971).
3. A. Martin:Nuovo Cimento,59 A, 131 (1968);Scattering theory: Unitarity, Analyticity and Crossing (Berlin, 1969);Conférence aux Rencontres de la R.C.P. No. 25, Strasbourg, Juin 1971.
4. R. G. Newton:Journ. Math. Phys.,9, 2050 (1968).
5. K. J. Foley, R. S. Gilmore, S. J. Lindenbaum, W. A. Love, S. Ozaki, E. H. Willen, R. Yamada andL. C. L. Yuan:Phys. Rev. Lett.,14, 862 (1965).