Isac, George, and M. Gabriela Cojocaru. “Functions Without Exceptional Family of Elements and the Solvability of Variational Inequalities on Unbounded Sets”. Topological Methods in Nonlinear Analysis 20, no. 2 (December 1, 2002): 375–391. Accessed July 22, 2024. https://apcz.umk.pl/TMNA/article/view/TMNA.2002.041.