RACHŮNKOVÁ, Irena. On the number of solutions of the Neumann problem for the ordinary second order differential equation. Annales Mathematicae Silesianae, [S. l.], v. 7, p. 79–87, 1993. Disponível em: https://journals.us.edu.pl/index.php/AMSIL/article/view/14248. Acesso em: 26 apr. 2025.