Counterexamples undeniably play an outstanding role in mathematics. As is known,
counterexamples are patently examples but with a different purpose. The commonly agreed …

This book is for third and fourth year university mathematics students (and Master students)
as well as lecturers and tutors in mathematics and anyone who needs the basic facts on …

Let B be a bounded self-adjoint operator and let A be a nonnegative self-adjoint unbounded
operator. It is shown that if BA is normal, it must be self-adjoint and so must be AB …

Maximality of linear operators | SpringerLink Skip to main content Advertisement SpringerLink
Account Menu Find a journal Publish with us Search Cart 1.Home 2.Rendiconti del Circolo …

In this paper, we show new versions of the Fuglede theorem in an unbounded setting. A
related counterexample is also presented. In the second part of the paper, we give a pair of …

Let A and B be two densely defined unbounded closeable operators in a Hilbert space such
that their unbounded operator products AB and BA are also densely defined. Then all four …

In this paper, we further investigate the problem of commutativity up to a factor (or λ-
commutativity) in the setting of bounded and unbounded linear operators in a complex …

ON THE COMMUTATIVITY OF CLOSED SYMMETRIC OPERATORS Page 1 Analysis Math.,
49 (3) (2023), 721–731 DOI: 10.1007/s10476-023-0226-2 ON THE COMMUTATIVITY OF …

arXiv:2203.06715v1 [math.FA] 13 Mar 2022 Page 1 arXiv:2203.06715v1 [math.FA] 13 Mar
2022 UNBOUNDED GENERALIZATIONS OF THE FUGLEDE-PUTNAM THEOREM SOUHEYB …

The present paper discusses Weiss' version of the Fuglede–Putnam theorem. We establish
three generalizations of this version, each of which involves unbounded normal operators …