1. G. Chew andF. Low: to be published.
2. N. N. Bogoljubov, B. V. Medvedev andM. K. Polivanov: lecture notes. Translated at the Institute for Advanced Study (Princeton 1957).
3. K. Symanzik:Phys. Rev.,743, 743 (1957).
4. R. Haag:Phys. Rev.,112, 669 (1958);W. Zimmermann:Nuovo Cimento,10, 567 (1958).
5. A related formulation which does not use asymptotic fields was given byK. Nishijima:Progr. Theor. Phys.,111, 995 (1958).