WEBB, J. R. L.; LAN, K. Q. Eigenvalue criteria for existence of multiple positive solutions of nonlinear boundary value problems of local and nonlocal type. Topological Methods in Nonlinear Analysis, [S. l.], v. 27, n. 1, p. 91–115, 2006. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.2006.003. Acesso em: 25 jan. 2022.