Korenevsky, D. G. “On the Averaging Principle for Hyperbolic Second Order Equations With a Functionally Disturbed Argument”. Ukrains’kyi Matematychnyi Zhurnal 23, no. 2 (February 23, 1971): 147–156. Accessed December 6, 2025. https://umj.imath.kiev.ua/index.php/umj/article/view/8497.