AGARWAL, P.; GRACE, S. R.; O’REGAN, D. Oscillation of certain fourth-order functional differential equations. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 59, n. 3, p. 291–313, 2007. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/3308. Acesso em: 5 dec. 2025.