Mitropolskiy YA. On the role of N.N. Bogolyubov in the development of the theory of nonlinear oscillations. Ukr. Mat. Zhurn. [Internet]. 1999Aug.25 [cited 2024Nov.24];51(8):1014–1035. Available from: https://umj.imath.kiev.ua/index.php/umj/article/view/4693