M. Kardel
Department of Mathematics, University Campus 2, University of Guilan, P.O. Box 1914, Rasht, Iran | (As a faculty member of (and supported by) Islamic Azad University, Zabol branch, Zabol, Iran. )
[ 1 ] - A characterization of orthogonality preserving operators
In this paper, we characterize the class of orthogonality preserving operators on an infinite-dimensional Hilbert space $H$ as scalar multiples of unitary operators between $H$ and some closed subspaces of $H$. We show that any circle (centered at the origin) is the spectrum of an orthogonality preserving operator. Also, we prove that every compact normal operator is a strongly orthogo...
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