Kogut, P. I. “High-Order Asymptotics of a Solution of One Problem of Optimal Control over a Distributed System With Rapidly Oscillating Coefficients”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 48, no. 7, July 1996, pp. 940-8, https://umj.imath.kiev.ua/index.php/umj/article/view/5266.