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Quasi-Contractions on Kreĭn Spaces
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A quasi-contraction, acting between Kreĭn spaces, is a linear bounded operator which is contractive when restricted to some subspace of finite codimension. If, in addition, the same property is satisfied by the adjoint of the operator, then it is called a double quasi-contraction. This paper is devoted to the investigation of basic properties of quasi-contractions and double quasi-contractions. Among others, we prove that the compression of a quasi-contraction (double quasi-contraction) to maximal uniformly negative subspaces is a semi-Fredholm operator (respectively, Fredholm operator) and we give a formula to compute its index. A spectral characterization of double quasi-contractions within the class of quasi-contractions is also obtained.
1993
1993-01-01
chapters
123-148
false
2019-04-16T08:59
https://link.springer.com/10.1007%2F978-3-0348-8575-1_7
en
chapter
readcube_id
bff4e048848667879e35428e67b2a6b67eab897bcf2a55b945c4ea3512517c1c
Pure Mathematics
Aurelian
Gheondea
Mathematical Sciences
pub.1040296755
dimensions_id
doi
10.1007/978-3-0348-8575-1_7
Basel
Birkhäuser Basel
A.
Gheondea
Timotin
D.
978-3-0348-9687-0
978-3-0348-8575-1
Operator Extensions, Interpolation of Functions and Related Topics
Institutul de Matematică, al Academiei Române, C.P. 1-764, 70700, Bucureşti, România
Vasilescu
F.-H.