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1
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Semi-Browder operators and perturbations

100%
Rakočević V.
Studia Mathematica
|
1997
|
tom 122
|
nr 2
131-137
EN
An operator in a Banach space is called upper (resp. lower) semi-Browder if it is upper (lower) semi-Fredholm and has a finite ascent (resp. descent). An operator in a Banach space is called semi-Browder if it is upper semi-Browder or lower semi-Browder. We prove the stability of the semi-Browder operators under commuting Riesz operator perturbations. As a corollary we get some results of Grabiner [6], Kaashoek and Lay [8], Lay [11], Rakočević [15] and Schechter [16].
2
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Invertibility of the commutator of an element in a C*-algebra and its Moore-Penrose inverse

64%
Benítez J., Rakočević V.
Studia Mathematica
|
2010
|
tom 200
|
nr 2
163-174
EN
We study the subset in a unital C*-algebra composed of elements a such that $aa^{†} - aa^{†}$ is invertible, where $a^{†}$ denotes the Moore-Penrose inverse of a. A distinguished subset of this set is also investigated. Furthermore we study sequences of elements belonging to the aforementioned subsets.
3
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Estimates for projections in Banach spaces and existence of direct complements

51%
Dirr G., Rakočević V., Wimmer H.
Studia Mathematica
|
2005
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tom 170
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nr 2
211-216
EN
Let W and L be complementary subspaces of a Banach space X and let P(W,L) denote the projection on W along L. We obtain a sufficient condition for a subspace M of X to be complementary to W and we derive estimates for the norm of P(W,L) - P(W,M).
4
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On the semi-Browder spectrum

51%
Kordula V., Müller V., Rakočević V.
Studia Mathematica
|
1997
|
tom 123
|
nr 1
1-13
EN
An operator in a Banach space is called upper (lower) semi-Browder if it is upper (lower) semi-Fredholm and has a finite ascent (descent). We extend this notion to n-tuples of commuting operators and show that this notion defines a joint spectrum. Further we study relations between semi-Browder and (essentially) semiregular operators.
5
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Lower s-numbers and their asymptotic behaviour

45%
Rakočević V., Zemánek J.
Studia Mathematica
|
1988
|
tom 91
|
nr 3
231-239
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