Mindeel. M. Al-Abrahemee, Khalid. “Solving Singular Perturbed Boundary Value Problems By Using Semi-Analytic Method”. Journal of Al-Qadisiyah for Computer Science and Mathematics, vol. 8, no. 1, Aug. 2017, pp. 67-77, https://jqcsm.qu.edu.iq/index.php/journalcm/article/view/45.