Lopatin, A.K. and Mitropolskiy, Y.A. (1994) “Bogolyubov averaging and normalization procedures in nonlinear mechanics. II”, Ukrains’kyi Matematychnyi Zhurnal, 46(11), pp. 1509–1526. Available at: https://umj.imath.kiev.ua/index.php/umj/article/view/5590 (Accessed: 14 April 2025).