Cheng SS, Shao YH. Comparison theorems and necessary/sufficient conditions for existence of nonoscillatory solutions of forced impulsive delay differential equations. Ukr. Mat. Zhurn. [Internet]. 2012Sep.25 [cited 2024Nov.24];64(9):1233-48. Available from: https://umj.imath.kiev.ua/index.php/umj/article/view/2654