On the closedness of the sum of ranges of operators $A_k$ with almost compact products $A_i^{\ast }{A}_j$

Ivan S. Feshchenko

Let ${\mathcal{H}}_1,\dots ,{\mathcal{H}}_n,\mathcal{H}$ be complex Hilbert spaces and $A_k:{\mathcal{H}}_k\to \mathcal{H}$ be a bounded linear operator with the closed range $Ran(A_k)$,…