AMSTER, P.; DE NÁPOLI, P. On a generalization of Lazer-Leach conditions for a system of second order ODE’s. Topological Methods in Nonlinear Analysis, [S. l.], v. 33, n. 1, p. 31–39, 2009. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.2009.003. Acesso em: 22 jul. 2024.