EL-Sayed A.M.A, Eman Hamdallah, and Ebead H.R. “Positive Solutions of an Initial Value Problem of a Delay-Self-Reference Nonlinear Differential Equation”. Malaya Journal of Matematik, vol. 8, no. 03, July 2020, pp. 1001-6, doi:10.26637/MJM0803/0046.