Koval’chukT. V., KravetsV. I., Mohyl’ovaV. V., and StanzhitskiiA. N. “Application of the method of Averaging to the Problems of Optimal Control over Functional-Differential Equations”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 70, no. 2, Feb. 2018, pp. 206-15, https://umj.imath.kiev.ua/index.php/umj/article/view/1551.