1. W. Heisenberg:Zeits. f. Phys.,120, 513, 673 (1943).
2. R. Haag:Dan,. Mat. Fys. Medd.,29, no. 12 (1955).
3. H. Lehmann, K. Stmanzik, W. Zimmermann:Nuovo Cimento,1, 425 (1955);. in the following quoted as LSZ I.
4. Polkinghoene Nuovo Cimento,4, 216 (1956) andProe. Cambr. Phil. Soc,53, 260 (1957)) has introduced a general type of product which depends not only on the space-time coordinates of the field operators, but also on additional parameters. For special choice of these parameters Polkinghorne’s product is identical with our R-product, as defined below in eq. (27).
5. K. Nishijima (to be published) has suggested a formulation of the asymptotic condition which avoids the operators of incoming and outgoing fields and may be obtained by taking matrix elements of (34″) with respect to Φ x1/in x1, Φ Β1/in. Β1 This modified procedure is useful to include the possibility of bound states in the formalism of r-functions, especially in connection with the completeness of the incoming and outgoing states (compare Appendix). We wish to thank Dr, Nishijima for informing us of his results prior to publication.