Aizicovici, S., Papageorgiou, N. S., & Staicu, V. (2010). Existence and multiplicity of solutions for resonant nonlinear Neumann problems. Topological Methods in Nonlinear Analysis, 35(2), 235–252. Retrieved from https://apcz.umk.pl/TMNA/article/view/TMNA.2010.014