K. AL- Saidy, S., and Z. Esa Abdul Naby. “Approximation of Functions by Means of the Modulus”. Journal of Al-Qadisiyah for Computer Science and Mathematics, Vol. 3, no. 2, Oct. 2017, pp. 156-65, https://qu.edu.iq/journalcm/index.php/journalcm/article/view/285.