Marano, S. A., and N. S. Papageorgiou. “Constant-Sign and Nodal Solutions for a Neumann Problem With $p$-Laplacian and Equi-Diffusive Reaction Term”. Topological Methods in Nonlinear Analysis, vol. 38, no. 2, Apr. 2011, pp. 233-48, https://apcz.umk.pl/TMNA/article/view/TMNA.2011.030.