N. Butris, Raad, and Ghada Shuker Jameel. “Periodic Solutions for Nonlinear System of Differential Equations of Third Order With Boundary Conditions”. Journal of Education and Science 26, no. 1 (March 1, 2013): 126–139. Accessed October 25, 2025. https://edusj.uomosul.edu.iq/index.php/edusj/article/view/41376.