GRETSKII, O. S. On the ?-differentiability of mappings of Banach spaces. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 46, n. 10, p. 1336–1342, 1994. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/5612. Acesso em: 6 dec. 2025.