Bainov, D. D., & Dimitrova, M. B. (1999). Sufficient Conditions for Oscillation of Solutions of Nonlinear Impulsive Differential Equations With a Retarded Argument. The Journal of the Indian Mathematical Society, 66(1-4), 49–59. Retrieved from https://informaticsjournals.co.in/index.php/jims/article/view/21931