Benharrat, Mohammed, and Bekkai Messirdi. “Relationship Between the Goldberg Spectrum and the B-Fredholm Spectra”. Sarajevo Journal of Mathematics 13, no. 1 (May 19, 2017): 81–91. Accessed October 16, 2024. https://sjm.anubih.ba/index.php/sjm/article/view/105.