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://trrest.vot.pl/ojsus/index.php/AMSIL/article/view/13991. Acesso em: 4 jul. 2025.