Allergretto, Walter, and Paolo Nistri. “Elliptic Equations With Discontinuous Nonlinearities”. Topological Methods in Nonlinear Analysis 2, no. 2 (December 1, 1993): 233–251. Accessed July 22, 2024. https://apcz.umk.pl/TMNA/article/view/TMNA.1993.041.