Papageorgiou, Nikolaos S., and George Smyrlis. “Positive Solutions for Nonlinear Nonhomogeneous Parametric Equations”. Topological Methods in Nonlinear Analysis 46, no. 1 (September 1, 2015): 1–15. Accessed July 22, 2024. https://apcz.umk.pl/TMNA/article/view/TMNA.2015.033.