WILCZYŃSKI, Paweł. Planar nonautonomous polynomial equations III. Zeros of the vector field. Topological Methods in Nonlinear Analysis, [S. l.], v. 40, n. 1, p. 71–110, 2012. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.2012.023. Acesso em: 4 jul. 2025.