Kostin, A. V., & Shchegolev, S. A. (1998). On solutions of a second-order quasilinear differential system representable by Fourier series with slowly varying parameters. Ukrains’kyi Matematychnyi Zhurnal, 50(5), 654–664. Retrieved from https://umj.imath.kiev.ua/index.php/umj/article/view/4903