Lykova О. B. Reduction principle in the Banach space. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 23, n. 4, p. 464–471, 1971. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/8580. Acesso em: 7 apr. 2025.