1. H. Umezawa, Y. Tomozawa. M. Konuma andS. Kamefuchi:Nuovo Cimento,3, 772 (1956);Proc. Theor. Phys.,15, 417 (1956). Hereafter the former will be referred to as I.
2. L. D. Landau, A. A. Abrikosov andI. M. Halatxikov:Doll. Akad. Nauk SSSR,95, 497, 733, 1177 (1954);96, 261 (1954);S. Kamefuchi andH. Umezawa:Nuovo Cimento,3, 1060 (1956);J. C. Taylor:Proc. Roy. Soc., A234, 296 (1956).
3. E. C. G. Stueckelberg andA. Petermann:Helr. Phys. Acta,26, 499 (1953);H. Umezawa andA. Visconti:Nuovo Cimento,1, 1079 (1055);N. N. Bogoliubov andD. V. Sirkov:Nuovo Cimento,3, 845 (1956).
4. A. A. Abrikosov, I. M. Halatxikov andA. D. Galamin:Boll. Akad. Nauk SSSR,97, 783 (1954).
5. J. C. Taylor:Pror. Roy. Soc, A234, 296 (1956).