ZU, Li; LIN, Xiaoning; JIANG, Daqing. 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: 4 jul. 2025.