1. N. N. Bogolyubov, Ukr. Matem. Zh.,2, 3 (1950); see also: Selected Works [in Russian], Vol. 2, Kiev (1970).
2. E. P. Solodovnikova, A. N. Tavkhelidze, and O. A. Khrustalev, Teor. Mat. Fiz.,10, 162 (1972).
3. P. N. Bogolyubov, Communication JINR R2-5684 [in Russian], Dubna (1971).
4. V. A. Matveev and A. N. Tavkhelidze, Preprint JINR R2-5141 [in Russian], Dubna (1970);
5. Report at the 15th International Conference on High-Energy Physics, Kiev (1970).