Kolomiyets VG, Samoilenko AM, Samoilenko VG. The Third Bogolyubov Readings. International Scientific Conference “Asymptotic and Qualitative Methods in the Theory of Nonlinear Oscillations”. Ukr. Mat. Zhurn. [Internet]. 1998Apr.25 [cited 2024Jul.27];50(4):599. Available from: https://umj.imath.kiev.ua/index.php/umj/article/view/4931