English

Counterexamples in isometric theory of symmetric and greedy bases

Functional Analysis 2023-04-13 v1

Abstract

We continue the study initiated in [F. Albiac and P. Wojtaszczyk, Characterization of 11-greedy bases, J. Approx. Theory 138 (2006), no. 1, 65-86] of properties related to greedy bases in the case when the constants involved are sharp, i.e., in the case when they are equal to 11. Our main goal here is to provide an example of a Banach space with a basis that satisfies Property (A) but fails to be 11-suppression unconditional, thus settling Problem 4.4 from [F. Albiac and J.L. Ansorena, Characterization of 11-almost greedy bases, Rev. Mat. Complut. 30 (2017), no. 1, 13-24]. In particular, our construction demonstrates that bases with Property (A) need not be 11-greedy even with the additional assumption that they are unconditional and symmetric. We also exhibit a finite-dimensional counterpart of this example and show that, at least in the finite-dimensional setting, Property (A) does not pass to the dual. As a by-product of our arguments, we prove that a symmetric basis is unconditional if and only if it is total, thus generalizing the well-known result that symmetric Schauder bases are unconditional.

Keywords

Cite

@article{arxiv.2304.05888,
  title  = {Counterexamples in isometric theory of symmetric and greedy bases},
  author = {Fernando Albiac and Jose L. Ansorena and Oscar Blasco and Hung Viet Chu and Timur Oikhberg},
  journal= {arXiv preprint arXiv:2304.05888},
  year   = {2023}
}