On the study of the positive solutions of a BVP under ψ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\psi $$\end{document}-Riemann–Liouville fractional derivative via upper and lower solution method

In this paper, we study the existence and uniqueness of a positive solution for a boundary value problem of nonlinear fractional integro-differential equations involving a generalized version of the Riemann–Liouville fractional derivative with respect to another function ψ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\psi $$\end{document} and integral boundary conditions. Using the Banach’s contraction principle and Schaefer’s fixed point theorem together with the upper and lower solution method we prove our main results. Finally, an example is presented to illuminate our theoretical results.