1. H. Lehmann, K. Symanzik andW. Zimmermann:Nuovo Cimento,1, 205 (1954);6, 319 (1957);V. Glaser, H. Lehmann andW. Zimmermann:Nuovo Cimento,6, 1122 (1957).
2. N. N. Boboliubov andD. V. Shirkov:Introduction to the Theory of Quantized Fields (New York, 1959);N. N. Bogoliubov, B. V. Medvedev andM. K. Polivanov:Voprossy teorii dispersionnykh sootnoshenii (Moscow, 1958).
3. See, for instance,A. S. Wightman:Recent Achievements in Axiomatic Field Theory, inTheoretical Physics (Vienna, 1963), where other references are given.
4. N. N. Bogoliubov andD. V. Shirkov loc. cit. in ref. (2);H. Bremermann, R. Oehme andJ. G. Taylor:Phys. Rev.,109, 2178 (1958);
5. F. J. Dyson:Phys. Rev.,110, 579 (1958).