Mіtrоpоlskу Yu. A., and Fоdchuk V. I. “Substantiation of the Averaging Method for Differential-Difference Equations in the Hilbert Space ”. Ukrains’kyi Matematychnyi Zhurnal 23, no. 6 (October 26, 1971): 745–752. Accessed December 5, 2025. https://umj.imath.kiev.ua/index.php/umj/article/view/8621.