1. L. B. Rédei: Umeå University preprint (1971), unpublished.
2. SeeN. N. Bogoliubov andD. V. Shirkov:Introduction to the Theory of Quantized Fields (New York, 1959), and references therein.
3. These are the well-known Heitler equations. See,e.g., inS. S. Schweber:An Introduction to Relativistic Quantum Field Theory (New York, 1961).
4. See, however, the recent preprint byR. Aviv, R. L. Sugar andR. Blankenbecler:Unitary models of multiparticle amplitudes, University of California, Santa Barbara, preprint (1972), where a model is presented which satisfies many-particle unitarity at infinite energy.
5. Another way to construct an interpolating field would be to use the logarithm of the scattering operator.H. Lehmann, K. Symanzik andW. Zimmermann:Nuovo Cimento,6, 319 (1957).