WARD, J. R. Periodic solutions of ordinary differential equations with bounded nonlinearities. Topological Methods in Nonlinear Analysis, [S. l.], v. 19, n. 2, p. 275–282, 2002. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.2002.014. Acesso em: 22 jul. 2024.