RICCERI B. Multiplicity theorems involving functions with non-convex range. Stud. Univ. Babeş-Bolyai Math. [Internet]. 2023 Mar. 20 [cited 2025 Feb. 5];68(1):125-37. Available from: https://studia.reviste.ubbcluj.ro/index.php/subbmathematica/article/view/4932