Papageorgiou, Nikolaos S., and Vicentiu D. Radulescu. “Solutions With Sign Information for Nonlinear Nonhomogeneous Elliptic Equations”. Topological Methods in Nonlinear Analysis 45, no. 2 (June 1, 2015): 575–600. Accessed March 29, 2024. https://apcz.umk.pl/TMNA/article/view/TMNA.2015.027.