Aizicovici, Sergiu, Nikolaos S. Papageorgiou, and Vasile Staicu. 2009. “On a $p$-Superlinear Neumann $p$-Laplacian Equation”. Topological Methods in Nonlinear Analysis 36 (1):111-30. https://apcz.umk.pl/TMNA/article/view/TMNA.2009.032.