FAIERMAN, M. Fredholm theory connected with a Douglis-Nirenberg system of differential equations over $\mathbb{R}^n$. Methods of Functional Analysis and Topology, [S. l.], v. 22, n. 4, p. 330–345, 2016. Disponível em: https://zen.imath.kiev.ua/index.php/mfat/article/view/645. Acesso em: 4 feb. 2026.