On a Sturm - Liouville like four point boundary value problem. Global Journal of Science Frontier Research, [S. l.], v. 12, n. F2, p. 19–22, 2012. Disponível em: https://www.journalofscience.org/index.php/GJSFR/article/view/100193. Acesso em: 6 feb. 2026.