Kolomiyets, V.G., Samoilenko, A.M. and Samoilenko, V.G. (1998) “The Third Bogolyubov Readings. International Scientific Conference ‘Asymptotic and Qualitative Methods in the Theory of Nonlinear Oscillations’”, Ukrains’kyi Matematychnyi Zhurnal, 50(4), p. 599. Available at: https://umj.imath.kiev.ua/index.php/umj/article/view/4931 (Accessed: 5 December 2025).