Slyusarchuk, V. V. “Conditions for Instability of an Invariant Toroidal Manifold of a Discrete Dynamical System in a Banach Space”. Ukrains’kyi Matematychnyi Zhurnal 53, no. 4 (April 25, 2001): 572–576. Accessed April 14, 2025. https://umj.imath.kiev.ua/index.php/umj/article/view/4280.