5 citations · 8 across the 12 of their papers we have counts for
7 papers · 1 filter
On the essential spectrum of the sum of self-adjoint operators and the closedness of the sum of operator ranges
Ivan S. Feshchenko
We get a criterion for 0 to be in the essential spectrum of a sum of self-adjoint operators whose pairwise products are compact. Using this result, we obtain necessary and sufficie…
On the divergence of series of the form \sum_{k=1}^\infty\|A_k x\|^p
Ivan Feshchenko
Let {A} be a system of operators. With any element x we associate the set of elements {Ax}. We study conditions under which there exists an element x such that the sum of p-th powe…
On absolutely representing families of subspaces in Banach spaces
Ivan S. Feshchenko
An absolutely representing family of subspaces is a natural generalization of an absolutely representing system of subspaces and absolutely representing system (of elements). We ob…
On systems of subspaces of a Hilbert space such that every pair of subspaces satisfies one of the angle or commutativity condition
Ivan Feshchenko, Alexander Strelets
We study finite systems of subspaces of a complex Hilbert space such that each pair of subspaces satisfies a certain condition as described in the following. For each subspace exce…
On the closedness of the sum of n subspaces of a Hilbert space
Ivan Feshchenko
We give necessary and sufficient conditions for the sum of n subspaces of a Hilbert space to be closed. We also present various properties of n-tuples of subspaces with closed sum.
On representing and absolutely representing systems of subspaces in Banach spaces
Ivan Feshchenko
We study properties of representing and absolutely representing systems of subspaces in Banach spaces. We also present sufficient conditions for the system of subspaces to be a rep…