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تسجيل مستخدم جديدCompact perturbations and consequent hereditarily polaroid operators
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تأليف
B. P. Duggal
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A Banach space operator $Ain B({cal{X}})$ is polaroid, $Ain {cal{P}}$, if the isolated points of the spectrum $sigma(A)$ are poles of the operator; $A$ is hereditarily polaroid, $Ain{cal{HP}}$, if every restriction of $A$ to a closed invariant subspace is polaroid. Operators $Ain{cal{HP}}$ have SVEP on $Phi_{sf}(A)={lambda: A-lambda$ is semi Fredholm $}$: This, in answer to a question posed by Li and Zhou (Studia Math. 221(2014), 175-192), proves the necessity of the condition $Phi_{sf}^+(A)=emptyset$. A sufficient condition for $Ain B({cal{X}})$ to have SVEP on $Phi_{sf}(A)$ is that its component $Omega_a(A)={lambdainPhi_{sf}(A): rm{ind}(A-lambda)leq 0}$ is connected. We prove: If $Ain B({cal{H}})$ is a Hilbert space operator, then a necessary and sufficient condition for there to exist a compact operator $K$ such that $A+Kin{cal{HP}}$ is that $Omega_a(A)$ is connected.
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