Abstract
The structure of unitary relations between Kreĭn spaces is investigated in geometrical terms. Two approaches are presented: The first approach relies on the so-called Weyl identity and the second approach is based on a graph decomposition of unitary relations. As a consequence of these investigations a quasi-block and a proper block representation of unitary operators are established. Both approaches yield also several new necessary and sufficient conditions for isometric relations to be unitary.
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Wietsma, H.L.: Block representation for classes of isometric operators between Kreĭn spaces. Submitted
Wietsma, H.L.: On unitary relations between Kreĭn spaces. Preprint. http://www.uwasa.fi/materiaali/pdf/isbn_978-952-476-356-1.pdf
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Wietsma, H.L. Representations of Unitary Relations Between Kreĭn Spaces. Integr. Equ. Oper. Theory 72, 309–344 (2012). https://doi.org/10.1007/s00020-011-1942-8
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DOI: https://doi.org/10.1007/s00020-011-1942-8