Frigon, Marlène. “On a Generalized Critical Point Theory on Gauge Spaces and Applications to Elliptic Problems on ${\mathbb R}^N$”. Topological Methods in Nonlinear Analysis 17, no. 1 (March 1, 2001): 67–89. Accessed April 26, 2024. https://apcz.umk.pl/TMNA/article/view/TMNA.2001.005.