GhanmiA. “Existence of Positive Solutions for a Coupled System of nonlinear fractional Differential Equations”. Ukrains’kyi Matematychnyi Zhurnal 71, no. 1 (January 25, 2019): 37-46. Accessed November 29, 2020. http://umj.imath.kiev.ua/index.php/umj/article/view/1417.