WAHASH, H. A.; PANCHAL, S. K. Positive solutions for generalized Caputo fractional differential equations using lower and upper solutions method. Journal of Fractional Calculus and Nonlinear Systems, [S. l.], v. 1, n. 1, p. 1–12, 2020. DOI: 10.48185/jfcns.v1i1.78. Disponível em: https://www.sabapub.com/index.php/jfcns/article/view/78. Acesso em: 29 oct. 2025.