PETROVSKII, Ya. B.; KHOMA, G. P. The solvability of a boundary-value periodic problem. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 49, n. 2, p. 302–308, 1997. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/5006. Acesso em: 11 apr. 2025.