1. N. N. Bogolyubov, A. A. Logunov, and I. T. Todorov, Foundations of the Axiomatic Approach in Quantum Field Theory [in Russian], Nauka, Moscow (1969).
2. N. N. Bogolyubov and D. V. Shirkov, Introduction to Quantum Field Theory [in Russian], Nauka, Moscow (1973).
3. E. B. Bogomol'nyi, ?Stability of classical solutions,? Yad. Fiz.,24, No. 4, 861?870 (1976).
4. V. Volterra, The Mathematical Theory of the Struggle for Existence [in Russian], Nauka, Moscow (1976).
5. W. Galois, Works [Russian translation], IL, Moscow (1936).