Dudzyanyi, S. I., and N. A. Perestyuk. 1998. “On the Stability of a Trivial Invariant Torus of One Class of Impulsive Systems”. Ukrains’kyi Matematychnyi Zhurnal 50 (3), 338–349. https://umj.imath.kiev.ua/index.php/umj/article/view/4935.