Mohammed S. Abdo & Satish K. Panchal. (2020). Fractional Integro-Differential Equations Involving $\psi$-Hilfer Fractional Derivative.
            <i>Advances in Applied Mathematics and Mechanics</i>. <i>11</i> (2).
            338-359.
         doi:10.4208/aamm.OA-2018-0143