Yakar, A., and H. Kutlay. “Extensions of Some Differential Inequalities for Fractional Integro-Differential Equations via Upper and Lower Solutions”. Bulletin of the Karaganda University. Mathematics Series 109, no. 1 (March 30, 2023): 156–167. Accessed July 10, 2025. https://mts.buketov.edu.kz/index.php/mathematics-vestnik/article/view/560.