RICCERI, Biagio. “Multiplicity Theorems Involving Functions With Non-Convex Range”. Studia Universitatis Babeș-Bolyai Mathematica 68, no. 1 (March 20, 2023): 125–137. Accessed January 19, 2026. https://studia.reviste.ubbcluj.ro/index.php/subbmathematica/article/view/4932.