Quoirin, Humberto Ramos, and Kenichiro Umezu. 2017. “An Indefinite Concave-Convex Equation under a Neumann Boundary Condition II”. Topological Methods in Nonlinear Analysis 49 (2):739-56. https://apcz.umk.pl/TMNA/article/view/TMNA.2017.007.