Perestyuk, N. A., and O. S. Chernikova. “On Stability of Integral Sets of Impulsive Differential Systems”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 54, no. 2, Feb. 2002, pp. 249-57, https://umj.imath.kiev.ua/index.php/umj/article/view/4060.