SHEN, C.; YANG, L.; LIANG, Y. Positive solutions for second order four-point boundary value problems at resonance. Topological Methods in Nonlinear Analysis, [S. l.], v. 38, n. 1, p. 1–15, 2011. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.2011.021. Acesso em: 20 jan. 2022.