LOPATIN, A. K.; MITROPOLSKIY, Yu. A. Bogolyubov averaging and normalization procedures in nonlinear mechanics. III. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 46, n. 12, p. 1627–1646, 1994. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/5574. Acesso em: 27 apr. 2025.