Continuity of the Essential Spectrum in the Class of Quasihyponormal Operators
Slaviša V. Đorđević (1998)
Matematički Vesnik
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Slaviša V. Đorđević (1998)
Matematički Vesnik
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Benharrat, Mohammed, Messirdi, Bekkai (2011)
Serdica Mathematical Journal
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2010 Mathematics Subject Classification: 47A10. We show that the symmetric difference between the generalized Kato spectrum and the essential spectrum defined in [7] by sec(T) = {l О C ; R(lI-T) is not closed } is at most countable and we also give some relationship between this spectrum and the SVEP theory.
Gh. Constantin (1975)
Matematički Vesnik
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V. Rakočević (1984)
Matematički Vesnik
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V. Rakočević (1981)
Matematički Vesnik
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Bucur, Amelia (1996)
General Mathematics
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V. Kordula, V. Müller (1996)
Studia Mathematica
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There are a number of spectra studied in the literature which do not fit into the axiomatic theory of Żelazko. This paper is an attempt to give an axiomatic theory for these spectra, which, apart from the usual types of spectra, like one-sided, approximate point or essential spectra, include also the local spectra, the Browder spectrum and various versions of the Apostol spectrum (studied under various names, e.g. regular, semiregular or essentially semiregular).
V. Rakočević (1985)
Matematički Vesnik
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GH. Mocanu (1974)
Studia Mathematica
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Vladimír Müller (1993)
Studia Mathematica
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We investigate relations between the spectra defined by Słodkowski [14] and higher Shilov boundaries of the Taylor spectrum. The results generalize the well-known relation between the approximate point spectrum and the usual Shilov boundary.
Catană, Petronela (2005)
Analele Ştiinţifice ale Universităţii “Ovidius" Constanţa. Seria: Matematică
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Andrzej Sołtysiak (1989)
Colloquium Mathematicae
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