Butris, R.N., and Azzam salahdin younis. “The Investigation of Solutions for Nonlinear System of Differential Equations With Boundary Conditions”. Journal of Education and Science 19, no. 3 (April 1, 2007): 71–86. Accessed September 10, 2025. https://edusj.uomosul.edu.iq/index.php/edusj/article/view/41296.