N. Butris, Raad, رعد, Ghada Shuker Jameel, and غادة. “Periodic Solutions for Nonlinear System of Differential Equations of Third Order With Boundary Conditions”. Journal of Education and Science (JES) 26, no. 1 (March 1, 2013): 126–139. Accessed August 4, 2025. https://rjps.uomosul.edu.iq/index.php/edusj/article/view/17229.