Papageorgiou, Nikolaos S., and Vicenţiu D. Rădulescu. “Positive Solutions for Parametric Semilinear Robin Problems With Indefinite and Unbounded Potential”. Mathematica Scandinavica 121, no. 2 (October 22, 2017): 263–292. Accessed July 24, 2026. https://journals.msp.org/mscand/article/view/296.