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Displaying 1001 – 1020 of 1284

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Subsequences of frames

R. Vershynin (2001)

Studia Mathematica

Every frame in Hilbert space contains a subsequence equivalent to an orthogonal basis. If a frame is n-dimensional then this subsequence has length (1 - ε)n. On the other hand, there is a frame which does not contain bases with brackets.

Subsets of nonempty joint spectrum in topological algebras

Antoni Wawrzyńczyk (2018)

Mathematica Bohemica

We give a necessary and a sufficient condition for a subset S of a locally convex Waelbroeck algebra 𝒜 to have a non-void left joint spectrum σ l ( S ) . In particular, for a Lie subalgebra L 𝒜 we have σ l ( L ) if and only if [ L , L ] generates in 𝒜 a proper left ideal. We also obtain a version of the spectral mapping formula for a modified left joint spectrum. Analogous theorems for the right joint spectrum and the Harte spectrum are also valid.

Subspaces of L p , p > 2, determined by partitions and weights

Dale E. Alspach, Simei Tong (2003)

Studia Mathematica

Many of the known complemented subspaces of L p have realizations as sequence spaces. In this paper a systematic approach to defining these spaces which uses partitions and weights is introduced. This approach gives a unified description of many well known complemented subspaces of L p . It is proved that the class of spaces with such norms is stable under (p,2) sums. By introducing the notion of an envelope norm, we obtain a necessary condition for a Banach sequence space with norm given by partitions...

Subspaces of ℓ₂(X) and Rad(X) without local unconditional structure

Ryszard A. Komorowski, Nicole Tomczak-Jaegermann (2002)

Studia Mathematica

It is shown that if a Banach space X is not isomorphic to a Hilbert space then the spaces ℓ₂(X) and Rad(X) contain a subspace Z without local unconditional structure, and therefore without an unconditional basis. Moreover, if X is of cotype r < ∞, then a subspace Z of ℓ₂(X) can be constructed without local unconditional structure but with 2-dimensional unconditional decomposition, hence also with basis.

Subspaces of the Bourgain-Delbaen space

Richard Haydon (2000)

Studia Mathematica

It is shown that every infinite-dimensional closed subspace of the Bourgain-Delbaen space X a , b has a subspace isomorphic to some p .

Currently displaying 1001 – 1020 of 1284