Anakira, N. R., A. Jameel, A.-K. Alomari, A. Saaban, M. Almahameed, and I. Hashim. “Approximate Solutions of Multi-Pantograph Type Delay Differential Equations Using Multistage Optimal Homotopy Asymptotic Method”. Journal of Mathematical and Fundamental Sciences, vol. 50, no. 3, Dec. 2018, pp. 221-32, doi:10.5614/j.math.fund.sci.2018.50.3.1.