SOROKA, Yu. Yu. Homeotopy groups for nonsingular foliations of the plane. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 69, n. 7, p. 1000–1008, 2017. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/1753. Acesso em: 5 dec. 2025.