CIESIELSKI, K. The Poincaré-Bendixson theorems for two-dimensional semiflows. Topological Methods in Nonlinear Analysis, [S. l.], v. 3, n. 1, p. 163–178, 1994. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.1994.007. Acesso em: 22 lip. 2024.