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Contractions of Class Q and Invariant Subspaces

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Abstract

A Hilbert Space operator T is of class Q ifT^{2*}T^2-2kern1ptT^*T+I is nonnegative. Every paranormaloperator is of class Q, but class-Q operators are notnecessarily normaloid. It is shown that if a class-Qcontraction T has no nontrivial invariant subspace, then it is aproper contraction. Moreover, the nonnegative operatorQ=T^{2*}T^2-2kern1ptT^*T+I also is a propercontraction.

참고문헌 (9)

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  5. B. P. Duggal,C. S. Kubrusly, "Paranormalcontractions and invariant subspaces", ,, 2003, pp.j40, 933~942
  6. T. Furuta., "Invitation to Linear Operators", 2001., ~
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  8. "Proper contractions andinvariant subspaces", 2001, pp.28, 223~230
  9. "Paranormal operators with countable spectrum are normal operators", 1987, pp.7, 591~

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