Astaf’eva, M. M., & Stepanenko, N. V. (2007). Sets of linear expansions of dynamical systems on a torus for a fixed Lyapunov function. Ukrains’kyi Matematychnyi Zhurnal, 59(12), 1707–1713. Retrieved from https://umj.imath.kiev.ua/index.php/umj/article/view/3425