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Unconditional families in Banach spaces

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Abstract

It is shown that for every separable Banach space X with non-separable dual, the space \(X^{**}\) contains an unconditional family of size \(|X^{**}|\) . The proof is based on Ramsey Theory for trees and finite products of perfect sets of reals. Among its consequences, it is proved that every dual Banach space has a separable quotient.

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Argyros, S.A., Dodos, P. & Kanellopoulos, V. Unconditional families in Banach spaces. Math. Ann. 341, 15–38 (2008). https://doi.org/10.1007/s00208-007-0179-y

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