KUDAYBERGENOV, K. K. $\nabla$-Fredgolm operators in Banach-Kantorovich spaces. Methods of Functional Analysis and Topology, [S. l.], v. 12, n. 3, p. 234–242, 2006. Disponível em: https://zen.imath.kiev.ua/index.php/mfat/article/view/316. Acesso em: 16 dec. 2025.