ValeevK. G. and VazhgovskayaM. Y. (1970) “Investigation of stability in resonance cases ”, Ukrains’kyi Matematychnyi Zhurnal, 23(1), pp. 63-70. Available at: https://umj.imath.kiev.ua/index.php/umj/article/view/8481 (Accessed: 27July2024).