LLIBRE, J. On the centers of cubic polynomial differential systems with four invariant straight lines. Topological Methods in Nonlinear Analysis, [S. l.], v. 55, n. 2, p. 387–402, 2020. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.2020.004. Acesso em: 24 apr. 2024.