MAKARENKOV, O. Influence of a small perturbation on Poincaré-Andronov operators with not well defined topological degree. Topological Methods in Nonlinear Analysis, [S. l.], v. 32, n. 1, p. 165–175, 2008. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.2008.043. Acesso em: 29 mar. 2024.