1. A. A. Logunov, Lectures in the Theory of Relativity and Gravitation [in Russian], Nauka, Moscow (1987).
2. N. I. Lobachevsky, Complete Collection of Works: Geometry [in Russian], Vol. 2, New Foundations of Geometry with a Complete Theory of Parallels, Gostechizdat, Moscow (1949).
3. M. Born and L. Infeld, Proc. Roy. Soc. London A, 144, 425–451 (1934).
4. W. Heisenberg and H. Euler, Z. Phys., 89, 714–732 (1936).
5. N. B. Narozhny, Sov. Phys. JETP, 28, 371–374 (1969).