DŁOTKO, Tadeusz. On a paper of Mawhin on second order differential equations. Annales Mathematicae Silesianae, [S. l.], v. 11, p. 55–66, 1997. Disponível em: https://journals.us.edu.pl/index.php/AMSIL/article/view/14184. Acesso em: 5 dec. 2025.