PRISHLYAK, A. O. Morse functions with finite number of singularities on a plane. Methods of Functional Analysis and Topology, [S. l.], v. 8, n. 1, p. 75–78, 2002. Disponível em: https://zen.imath.kiev.ua/index.php/mfat/article/view/178. Acesso em: 18 dec. 2025.