Mohamed Houas. “Sequential Fractional Pantograph Differential Equations With Nonlocal Boundary Conditions: Uniqueness and Ulam-Hyers-Rassias Stability”. Results in Nonlinear Analysis, vol. 5, no. 1, Nov. 2022, pp. 29-41, https://nonlinear-analysis.com/index.php/pub/article/view/83.