N. Butrus, Raed, and Mirna A. Azeez. “Some Theorems in Existence and Oneness of a System of Integral - Nonlinear Differential Equations”. Journal of Education and Science (JES) 18, no. 2 (June 1, 2006): 76–89. Accessed August 6, 2025. https://ojs.uomosul.edu.iq/index.php/edusj/article/view/23573.