HABETS, P.; GAUDENZI, M. Existence and multiplicity of positive solutions for boundary value problems of 2d order ODE. Topological Methods in Nonlinear Analysis, [S. l.], v. 14, n. 1, p. 131–150, 1999. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.1999.024. Acesso em: 19 apr. 2024.