1. N. N. Bogolyubov, Selected Works [in Russian], Vol. 2, Naukova Dumka (1970), pp. 499. (Ukr. Matem. Zh.,2, No. 2, 3?24 (1950).
2. E. P. Solodovnikova, A. N. Tavkhelidze, and O. A. Khrustalev, Teor. Mat. Fiz.,10, 162 (1972);11, 317 (1972).
3. E. P. Solodovnikova, A. N. Tavkhelidze, and O. A. Khrustalev, Teor. Mat. Fiz.,12, 164 (1972).
4. N. E. Tyurin and A. V. Shurgaya, Preprint IFVE 75-19, 72-32 [in Russian], Serpukhov (1972);
5. O. D. Timofeevskaya, N. E. Tyurin, and A. V. Shurgaya, Preprint 72-62, IFVE [in Russian] (1972).