HAVRAN, V. S. Simple derivations of higher degree in two variables. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 61, n. 4, p. 568–571, 2009. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/3041. Acesso em: 14 apr. 2025.