PRISHLYAK, A. O.; BONDARENKO, A. M. Maps of 2-manifolds into the plane. Methods of Functional Analysis and Topology, [S. l.], v. 18, n. 3, p. 220–229, 2012. Disponível em: https://zen.imath.kiev.ua/index.php/mfat/article/view/518. Acesso em: 16 dec. 2025.