TSAMATOS, P. C. Double positive solutions for second order nonlocal functional and ordinary boundary value problems. Topological Methods in Nonlinear Analysis, [S. l.], v. 28, n. 1, p. 117–131, 2006. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.2006.023. Acesso em: 25 jan. 2022.