CHENG, Sui Sun; SHAO, Yuan Huang. Comparison theorems and necessary/sufficient conditions for existence of nonoscillatory solutions of forced impulsive delay differential equations. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 64, n. 9, p. 1233–1248, 2012. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/2654. Acesso em: 6 dec. 2025.