Tawfiq, Luma. N. M., and Heba. W. Rasheed. “On Solution of Regular Singular Ordinary Boundary Value Problem”. Ibn AL-Haitham Journal For Pure and Applied Sciences, vol. 26, no. 2, Apr. 2017, pp. 249-56, https://jih.uobaghdad.edu.iq/index.php/j/article/view/473.