EfendievV. V., and ZheltikovV. P. “Averaging of Boundary-Value Problems of Control over a Standard System With Delay”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 48, no. 4, Apr. 1996, pp. 548-53, https://umj.imath.kiev.ua/index.php/umj/article/view/5319.