MitropolskyY. A., & FоdchukV. I. (1966). Asymptotic methods of nonlinear mechanics as applied to nonlinear differential equations with delayed argument. Ukrains’kyi Matematychnyi Zhurnal, 18(3), 65-84. Retrieved from https://umj.imath.kiev.ua/index.php/umj/article/view/8738