KRASNOSEL’SKIĬ, A. Index at infinity and bifurcations of twice degenerate vector fields. Topological Methods in Nonlinear Analysis, [S. l.], v. 35, n. 1, p. 99–126, 2010. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.2010.007. Acesso em: 19 apr. 2024.