Ignat’ev, A. O., and KonosevichВ. I. “On the Stability of Invariant Sets of a System of Autonomous Differential Equations under Constantly Acting Perturbations”. Ukrains’kyi Matematychnyi Zhurnal 51, no. 9 (September 25, 1999): 1287–1291. Accessed March 7, 2025. https://umj.imath.kiev.ua/index.php/umj/article/view/4725.