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3. W. I. Skrypnyk, “On holomorphic solutions of Darwin equations of motion of point charges,” Ukr. Mat. Zh., 65, No. 4, 546–554 (2013); English translation: Ukr. Math. J., 65, No. 4, 602–611 (2013).
4. W. Skrypnik, “On exact solutions of Coulomb equation of motion of planar charges,” J. Geom. Phys., 98, 285–291 (2015).
5. A. M. Lyapunov, General Problem of Stability of Motion [in Russian], Gostekhizdat, Moscow (1950); English translation: Int. J. Contr., 55, No. 3, 521–790 (1992).