Rasulov T, Dilmurodov EB. Estimates for the Bounds of the Essential Spectrum of a 2 × 2 Operator Matrix. Contemp. Math. [Internet]. 2020 Jul. 17 [cited 2024 Apr. 18];1(4):170-86. Available from: https://ojs.wiserpub.com/index.php/CM/article/view/409