LIPCHAN, V. V. On the existence of an invariant manifold for weakly nonlinear matrix differential equations. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 48, n. 3, p. 422–424, 1996. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/5340. Acesso em: 5 dec. 2025.