Ignat'ev, A.O. and Konosevich В.I. (1999) “On the stability of invariant sets of a system of autonomous differential equations under constantly acting perturbations”, Ukrains’kyi Matematychnyi Zhurnal, 51(9), pp. 1287–1291. Available at: https://umj.imath.kiev.ua/index.php/umj/article/view/4725 (Accessed: 5 December 2025).