Golets, V.L. (1970) “On the Problem of Disturbance of Stable Invariant Tore of the Dynamic System ”, Ukrains’kyi Matematychnyi Zhurnal, 23(1), pp. 130–137. Available at: https://umj.imath.kiev.ua/index.php/umj/article/view/8495 (Accessed: 10 April 2025).