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2. A. P. Kotel'nikov, in: In Memorial N. I. Lobachevskii, Vol. 3, Kazan' (1927), pp. 37?64.
3. V. A. Fock, The Theory of Space, Time and Gravitation, Oxford (1964).
4. N. A. Chernikov, Preprint R-723 [in Russian], JINR, Dubna (1961).
5. N. A. Chernikov, Preprint R2-10251 [in Russian], JINR, Dubna (1976).