FONDA, A.; TOADER, R. Lower and upper solutions to semilinear boundary value problems: an abstract approach. Topological Methods in Nonlinear Analysis, [S. l.], v. 38, n. 1, p. 59–93, 2011. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.2011.024. Acesso em: 26 apr. 2024.