ZverkovaT. S., and PlotnikovV. A. “Method of Partial Averaging in the Systems of Standard Form With Discontinuous Right-Hand Sides”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 45, no. 1, Jan. 1993, pp. 140–142, https://umj.imath.kiev.ua/index.php/umj/article/view/5794.