FONDA, Alessandro; GARRIONE, Maurizio. Generalized Sturm-Liouville boundary conditions for first order differential systems in the plane. Topological Methods in Nonlinear Analysis, [S. l.], v. 42, n. 2, p. 293–325, 2013. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.2013.038. Acesso em: 8 jul. 2025.