Existence of an invariant torus for a degenerate linear extension of a dynamical system. Neliniini Kolyvannya, [S. l.], v. 19, n. 2, p. 217–226, 2016. Disponível em: https://twinhead.imath.kiev.ua/index.php/nosc/article/view/824. Acesso em: 8 dec. 2025.