CHERN, H.-Y. Nonlinear Sturm-Liouville problems for systems of ordinary differential equations. Topological Methods in Nonlinear Analysis, [S. l.], v. 5, n. 1, p. 193–209, 1995. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.1995.011. Acesso em: 22 jul. 2024.