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Essential approximate point spectra and Weyl’s theorem for operator matrices. (English) Zbl 1083.47006
The authors characterize the essential approximate point spectrum and Weyl spectrum of a $2\times 2$ upper triangular operator matrix $M_C$, where $M_C=\left(\smallmatrix A&C\\ 0&B\endsmallmatrix\right)$ is an operator acting on the Hilbert space $\Cal{H}\oplus \Cal{K}$. In addition, the authors consider Weyl’s theorem, Browder’s theorem, a-Weyl’s theorem and a-Browder’s theorem for $M_C$.

##### MSC:
 47A10 Spectrum and resolvent of linear operators 47A53 (Semi-) Fredholm operators; index theories
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##### References:
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