SamoilenkoA. M., and SlyusarchukV. V. “Discrete Dynamical Systems With Invariant Asymptotically Stable Toroidal Manifold”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 51, no. 4, Apr. 1999, pp. 466–471, https://umj.imath.kiev.ua/index.php/umj/article/view/4632.