NICULESCU, C. P.; RADULESCU, V. A saddle point theorem for non-smooth functionals and problems at resonance. Annales Fennici Mathematici, [S. l.], v. 21, n. 1, p. 117–131, 1996. Disponível em: https://afm.journal.fi/article/view/134857. Acesso em: 25 nov. 2024.