Mіtrоpоlskу Y.A. and Fоdchuk V.I. (1971) “Substantiation of the averaging method for differential-difference equations in the Hilbert space ”, Ukrains’kyi Matematychnyi Zhurnal, 23(6), pp. 745–752. Available at: https://umj.imath.kiev.ua/index.php/umj/article/view/8621 (Accessed: 5 December 2025).