Bujukliev, Nikolay. “Linear Cross-Sections and Fredholm Operators in a Class Groupoid $C^*$-Algebras”. Ann. Sofia Univ. Fac. Math. and Inf. 108 (December 12, 2021): 17–21. Accessed November 24, 2024. https://ftl5.uni-sofia.bg./index.php/fmi/article/view/550.