GRUSHKOVSKAYA, V. V. An estimation of decay for solutions of nonlinear systems with equal frequencies. Transactions of Institute of Mathematics, the NAS of Ukraine, [S. l.], v. 13, n. 3, p. 69–84, 2016. Disponível em: https://trim.imath.kiev.ua/index.php/trim/article/view/33. Acesso em: 20 jul. 2024.