ZU, L.; LIN, X.; JIANG, D. Existence theory for single and multiple solutions to singular boundary value problems for second order impulsive differential equations. Topological Methods in Nonlinear Analysis, [S. l.], v. 30, n. 1, p. 171–191, 2007. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.2007.024. Acesso em: 22 jul. 2024.