LIGĘZA, Jan. Existence of generalized, positive and periodic solutions for some differential equations of order II. Annales Mathematicae Silesianae, [S. l.], v. 28, p. 59–86, 2014. Disponível em: https://journals.us.edu.pl/index.php/AMSIL/article/view/13991. Acesso em: 5 dec. 2025.