He, Ji-Huan. “Application of Topological Technology to Construction of a Perturbation System for a Strongly Nonlinear Equation”. Topological Methods in Nonlinear Analysis 20, no. 1 (September 1, 2002): 77–84. Accessed April 19, 2024. https://apcz.umk.pl/TMNA/article/view/TMNA.2002.026.