Wang, Hui, Lingling Zhang, and Xiaoqiang Wang. “New Unique Existence Criteria for Higher-Order Nonlinear Singular Fractional Differential Equations”. Nonlinear Analysis: Modelling and Control 24, no. 1 (December 14, 2018): 95–120. Accessed July 6, 2025. https://www.zurnalai.vu.lt/nonlinear-analysis/article/view/12920.