BilenkoV. I., BozhonokK. V., and DzyadykS. Y. “Piecewise-Polynomial approximations for the Solutions of Impulsive Differential Equations”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 71, no. 2, Feb. 2019, pp. 168-79, https://umj.imath.kiev.ua/index.php/umj/article/view/1429.