Chen, Jianqing, Nikolaos S. Papageorgiou, and Eugénio M. Rocha. “Twin Positive Solutions for Singular Nonlinear Elliptic Equations”. Topological Methods in Nonlinear Analysis 35, no. 1 (April 23, 2010): 187–201. Accessed July 3, 2024. https://apcz.umk.pl/TMNA/article/view/TMNA.2010.011.