PRISHLYAK, A. O.; LYCHAK, D. P. Morse functions and flows on nonorientable surfaces. Methods of Functional Analysis and Topology, [S. l.], v. 15, n. 3, p. 251–258, 2009. Disponível em: https://zen.imath.kiev.ua/index.php/mfat/article/view/422. Acesso em: 17 dec. 2025.