Guo, Limin, and Lishan Liu. “Maximal and Minimal Iterative Positive Solutions for Singular Infinite-Point P-Laplacian Fractional Differential Equations”. Nonlinear Analysis: Modelling and Control, vol. 23, no. 6, June 2019, pp. 851-65, https://doi.org/10.15388/NA.2018.6.3.