Wyniki wyszukiwania - Biblioteka Nauki

1

On embeddings of C₀(K) spaces into C₀(L,X) spaces

100%

Candido L.

Studia Mathematica

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2016

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tom 232

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nr 1

1-6

EN

For a locally compact Hausdorff space K and a Banach space X let C₀(K, X) denote the space of all continuous functions f:K → X which vanish at infinity, equipped with the supremum norm. If X is the scalar field, we denote C₀(K, X) simply by C₀(K). We prove that for locally compact Hausdorff spaces K and L and for a Banach space X containing no copy of c₀, if there is an isomorphic embedding of C₀(K) into C₀(L,X), then either K is finite or |K| ≤ |L|. As a consequence, if there is an isomorphic embedding of C₀(K) into C₀(L,X) where X contains no copy of c₀ and L is scattered, then K must be scattered.

2

On complemented copies of c₀(ω₁) in C(Kⁿ) spaces

63%

Candido L. , Koszmider P.

Studia Mathematica

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2016

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tom 233

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nr 3

209-226

EN

Given a compact Hausdorff space K we consider the Banach space of real continuous functions C(Kⁿ) or equivalently the n-fold injective tensor product $⊗̂^{n}_{ε}C(K)$ or the Banach space of vector valued continuous functions C(K,C(K,C(K...,C(K)...). We address the question of the existence of complemented copies of c₀(ω₁) in $⊗̂^{n}_{ε} C(K)$ under the hypothesis that C(K) contains such a copy. This is related to the results of E. Saab and P. Saab that $X ⊗̂_{ε} Y$ contains a complemented copy of c₀ if one of the infinite-dimensional Banach spaces X or Y contains a copy of c₀, and of E. M. Galego and J. Hagler that it follows from Martin's Maximum that if C(K) has density ω₁ and contains a copy of c₀(ω₁), then C(K×K) contains a complemented copy of c₀(ω₁). Our main result is that under the assumption of ♣ for every n ∈ ℕ there is a compact Hausdorff space Kₙ of weight ω₁ such that C(K) is Lindelöf in the weak topology, C(Kₙ) contains a copy of c₀(ω₁), C(Kₙⁿ) does not contain a complemented copy of c₀(ω₁), while $C(Kₙ^{n+1})$ does contain a complemented copy of c₀(ω₁). This shows that additional set-theoretic assumptions in Galego and Hagler's nonseparable version of Cembrano and Freniche's theorem are necessary, as well as clarifies in the negative direction the matter unsettled in a paper of Dow, Junnila and Pelant whether half-pcc Banach spaces must be weakly pcc.

3

How far is C(ω) from the other C(K) spaces?

63%

Candido L. , Galego E.

Studia Mathematica

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2013

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tom 217

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nr 2

123-138

EN

Let us denote by C(α) the classical Banach space C(K) when K is the interval of ordinals [1,α] endowed with the order topology. In the present paper, we give an answer to a 1960 Bessaga and Pełczyński question by providing tight bounds for the Banach-Mazur distance between C(ω) and any other C(K) space which is isomorphic to it. More precisely, we obtain lower bounds L(n,k) and upper bounds U(n,k) on d(C(ω),C(ωⁿk)) such that U(n,k) - L(n,k) < 2 for all 1 ≤ n, k < ω.

4

Embeddings of C(K) spaces into C(S,X) spaces with distortion strictly less than 3

63%

Candido L. , Galego E.

Fundamenta Mathematicae

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2013

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tom 220

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nr 1

83-92

EN

In the spirit of the classical Banach-Stone theorem, we prove that if K and S are intervals of ordinals and X is a Banach space having non-trivial cotype, then the existence of an isomorphism T from C(K, X) onto C(S,X) with distortion $||T|| ||T^{-1}||$ strictly less than 3 implies that some finite topological sum of K is homeomorphic to some finite topological sum of S. Moreover, if Xⁿ contains no subspace isomorphic to $X^{n+1}$ for every n ∈ ℕ, then K is homeomorphic to S. In other words, we obtain a vector-valued Banach-Stone theorem which is an extension of a Gordon theorem and at the same time an improvement of a Behrends and Cambern theorem. In order to prove this, we show that if there exists an embedding T of a C(K) space into a C(S,X) space, with distortion strictly less than 3, then the cardinality of the αth derivative of S is finite or greater than or equal to the cardinality of the αth derivative of K, for every ordinal α.

5

How far is C₀(Γ,X) with Γ discrete from C₀(K,X) spaces?

63%

Candido L. , Galego E.

Fundamenta Mathematicae

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2012

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tom 218

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nr 2

151-163

EN

For a locally compact Hausdorff space K and a Banach space X we denote by C₀(K,X) the space of X-valued continuous functions on K which vanish at infinity, provided with the supremum norm. Let n be a positive integer, Γ an infinite set with the discrete topology, and X a Banach space having non-trivial cotype. We first prove that if the nth derived set of K is not empty, then the Banach-Mazur distance between C₀(Γ,X) and C₀(K,X) is greater than or equal to 2n + 1. We also show that the Banach-Mazur distance between C₀(ℕ,X) and C([1,ωⁿk],X) is exactly 2n + 1, for any positive integers n and k. These results extend and provide a vector-valued version of some 1970 Cambern theorems, concerning the cases where n = 1 and X is the scalar field.