Mitropolsky, Y. A., and Fоdchuk V. I. “Asymptotic Methods of Nonlinear Mechanics As Applied to Nonlinear Differential Equations With Delayed Argument”. Ukrains’kyi Matematychnyi Zhurnal 18, no. 3 (April 27, 1966): 65–84. Accessed December 5, 2025. https://umj.imath.kiev.ua/index.php/umj/article/view/8738.