1. N. N. Bogolyubov, ?A new form of adiabatic perturbation theory in the problem of the interaction of a particle with a quantum field,? Ukr. Mat. Zh.,2, No. 2, 3 (1950).
2. S. V. Tyablikov, ?Adiabatic form of perturbation theory in the problem of the interaction of a particle with a quantum field,? Zh. Eksp. Teor. Fiz.,21, 337 (1951).
3. E. M. Henley and W. Thirring, Elementary Quantum Field Theory, McGraw-Hill, New York (1962).
4. S. S. Schweber, H. A. Bethe, and F. de Hoffman, Mesons and Fields, Vol. 2, Peterson Row, Evanston, Ill. (1955).
5. E. P. Solodovnikova, A. N. Tavkhelidze, and O. A. Khrustalev, ?Bogolyubov transformations in the theory of strong coupling,? Teor. Mat. Fiz.,11, 317 (1972).