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Generalized Weyl's Theorem for Some Classes of Operators

Salah Mecheri
경북대학교 자연과학대학 수학과|2006.12|Kyungpook Mathematical Journal|제46권 제4호|pp. 553-563

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Abstract

Let A be a bounded linear operator acting on a Hilbert space H. The B-Weyl spectrum of A is the set ¾Bw(A) of all ¸ 2 C such that A¡¸I is not a B-Fredholm operator of index 0. Let E(A) be the set of all isolated eigenvalues of A. Recently in [6] Berkani showed that if A is a hyponormal operator, then A satisfies generalized Weyl’s theorem ¾Bw(A) = ¾(A) n E(A), and the B-Weyl spectrum ¾Bw(A) of A satisfies the spectral mapping theorem. In [51], H. Weyl proved that weyl’s theorem holds for hermitian operators. Weyl’s theorem has been extended from hermitian operators to hyponormal and Toeplitz operators [12], and to several classes of operators including semi-normal operators ([9], [10]). Recently W. Y. Lee [35] showed that Weyl’s theorem holds for algebraically hyponormal operators. R. Curto and Y. M. Han [14] have extended Lee’s results to algebraically paranormal operators. In [19] the authors showed that Weyl’s theorem holds for algebraically p-hyponormal operators. As Berkani has shown in [5], if the generalized Weyl’s theorem holds for A, then so does Weyl’s theorem. In this paper all the above results are generalized by proving that generalizedWeyl’s theorem holds for the case where A is an algebraically (p; k)-quasihyponormal or an algebarically paranormal operator which includes all the above mentioned operators.

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