Ganji, Z. Z., et al. “Application of the Homotopy Perturbation Method to Coupled System of Partial Differential Equations With Time Fractional Derivatives”. Topological Methods in Nonlinear Analysis, vol. 31, no. 2, June 2008, pp. 341-8, https://apcz.umk.pl/TMNA/article/view/TMNA.2008.025.