LOPATIN, A. K.; MITROPOLSKIY, Yu. A. Bogolyubov averaging and normalization procedures in nonlinear mechanics. II. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 46, n. 11, p. 1509–1526, 1994. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/5590. Acesso em: 14 apr. 2025.