MALTA, I.; SALDANHA, N. C.; TOMEI, C. Morin singularities and global geometry in a class of ordinary differential operators. Topological Methods in Nonlinear Analysis, [S. l.], v. 10, n. 1, p. 137–169, 1997. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.1997.026. Acesso em: 22 jul. 2024.