Feng, Xinlong, Yinnian He, and Jixiang Meng. “Application of Homotopy Perturbation Method to the Bratu-Type Equations”. Topological Methods in Nonlinear Analysis 31, no. 2 (June 1, 2008): 243–252. Accessed October 16, 2021. https://apcz.umk.pl/TMNA/article/view/TMNA.2008.015.