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On the principle of local reflexivity

Ehrhard Behrends — 1991

Studia Mathematica

We prove a version of the local reflexivity theorem which is, in a sense, the most general one: our main theorem characterizes the conditions which can be imposed additionally on the usual local reflexivity map provided that these conditions are of a certain general type. It is then shown how known and new local reflexivity theorems can be derived. In particular, the compatibility of the local reflexivity map with subspaces and operators is investigated.

On Bárány's theorems of Carathéodory and Helly type

Ehrhard Behrends — 2000

Studia Mathematica

The paper begins with a self-contained and short development of Bárány’s theorems of Carathéodory and Helly type in finite-dimensional spaces together with some new variants. In the second half the possible generalizations of these results to arbitrary Banach spaces are investigated. The Carathéodory-Bárány theorem has a counterpart in arbitrary dimensions under suitable uniform compactness or uniform boundedness conditions. The proper generalization of the Helly-Bárány theorem reads as follows:...

Products of n open subsets in the space of continuous functions on [0,1]

Ehrhard Behrends — 2011

Studia Mathematica

Let O₁,...,Oₙ be open sets in C[0,1], the space of real-valued continuous functions on [0,1]. The product O₁ ⋯ Oₙ will in general not be open, and in order to understand when this can happen we study the following problem: given f₁,..., fₙ ∈ C[0,1], when is it true that f₁ ⋯ fₙ lies in the interior of B ε ( f ) B ε ( f ) for all ε > 0 ? ( B ε denotes the closed ball with radius ε and centre f.) The main result of this paper is a characterization in terms of the walk t ↦ γ(t): = (f₁(t),..., fₙ(t)) in ℝⁿ. It has to...

Strongly mixing sequences of measure preserving transformations

Ehrhard BehrendsJörg Schmeling — 2001

Czechoslovak Mathematical Journal

We call a sequence ( T n ) of measure preserving transformations strongly mixing if P ( T n - 1 A B ) tends to P ( A ) P ( B ) for arbitrary measurable A , B . We investigate whether one can pass to a suitable subsequence ( T n k ) such that 1 K k = 1 K f ( T n k ) f d P almost surely for all (or “many”) integrable f .

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