Abdo, M. S., S. K. Panchal, and H. Shafei Hussien. “Fractional Integro-Differential Equations With Nonlocal Conditions and ψ–Hilfer Fractional Derivative”. Mathematical Modelling and Analysis, vol. 24, no. 4, Oct. 2019, pp. 564-8, doi:10.3846/mma.2019.034.