Faierman, M. (2016) “Fredholm theory connected with a Douglis-Nirenberg system of differential equations over $\mathbb{R}^n$”, Methods of Functional Analysis and Topology, 22(4), pp. 330–345. Available at: https://zen.imath.kiev.ua/index.php/mfat/article/view/645 (Accessed: 16 December 2025).