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## Studia Mathematica

2009 | 195 | 3 | 243-255
Tytuł artykułu

### Johnson's projection, Kalton's property (M*), and M-ideals of compact operators

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Let X and Y be Banach spaces. We give a "non-separable" proof of the Kalton-Werner-Lima-Oja theorem that the subspace 𝒦(X,X) of compact operators forms an M-ideal in the space 𝓛(X,X) of all continuous linear operators from X to X if and only if X has Kalton's property (M*) and the metric compact approximation property. Our proof is a quick consequence of two main results. First, we describe how Johnson's projection P on 𝓛(X,Y)* applies to f ∈ 𝓛(X,Y)* when f is represented via a Borel (with respect to the relative weak* topology) measure on $\overline{B_{X**} ⊗ B_{Y*}}^{w*} ⊂ 𝓛(X,Y)*$: If Y* has the Radon-Nikodým property, then P "passes under the integral sign". Our basic theorem en route to this description-a structure theorem for Borel probability measures on $\overline{B_{X**} ⊗ B_{Y*}}^{w*}$-also yields a description of 𝒦(X,Y)* due to Feder and Saphar. Second, we show that property (M*) for X is equivalent to every functional in $\overline{B_{X**} ⊗ B_{X*}}^{w*}$ behaving as if 𝒦(X,X) were an M-ideal in 𝓛(X,X).
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Tom
Numer
Strony
243-255
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Daty
wydano
2009
Twórcy
autor
• Department of Mathematics, Agder University, Servicebox 422, 4604 Kristiansand, Norway
autor
• Institute of Mathematics, University of Tartu, J. Liivi 2, 50409 Tartu, Estonia
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