Wahash, Hanan A., and Satish K. Panchal. “Positive Solutions for Generalized Caputo Fractional Differential Equations Using Lower and Upper Solutions Method”. Journal of Fractional Calculus and Nonlinear Systems 1, no. 1 (December 30, 2020): 1–12. Accessed April 20, 2024. https://sabapub.com/index.php/jfcns/article/view/78.