B. P. Bazhura and A. M. Samoilenko, “Investigation of a dynamical system in a neighborhood of an invariant toroidal manifold in the general case”, Ukr. Mat. Zhurn., vol. 46, no. 10, pp. 1399–1408, Oct. 1994, Accessed: Apr. 16, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/5620