N. R. Anakira, 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”, J. Math. Fund. Sci., vol. 50, no. 3, pp. 221-232, Dec. 2018.