Marano, S. A. and Motreanu, D. (2003) “A deformation theorem and some critical point results for non-differentiable functions”, Topological Methods in Nonlinear Analysis, 22(1), pp. 139–158. Available at: https://apcz.umk.pl/TMNA/article/view/TMNA.2003.032 (Accessed: 3 July 2024).