Kulik, V. L. “Construction of Lyapunov Functions in the Theory of Regular Linear Extensions of Dynamical Systems on a Torus”. Ukrains’kyi Matematychnyi Zhurnal 67, no. 10 (October 25, 2015): 1358–1365. Accessed April 14, 2025. https://umj.imath.kiev.ua/index.php/umj/article/view/2072.