GIRYK, O. A. Classification of polar Morse-Smale vector fields on two-dimensional manifolds. Methods of Functional Analysis and Topology, [S. l.], v. 2, n. 1, p. 23–37, 1996. Disponível em: https://zen.imath.kiev.ua/index.php/mfat/article/view/8. Acesso em: 4 feb. 2026.