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Coordinate systems in Banach spaces and lattices

by A. Aviles and C. Rosendal and M. Taylor and P. Tradacete

(Report number 2024-20)

Abstract
Using methods of descriptive set theory, in particular, the determinacy of infinite games of perfect information, we answer several questions from the literature regarding different notions of bases in Banach spaces and lattices. For the case of Banach lattices, our results follow from a general theorem stating that (under the assumption of projective determinacy), every order basis $(e_n)$ for a Banach lattice $X=[e_n]$ is also a $\sigma$-order basis for $X$, every $\sigma$-order basis for $X$ is a uniform basis for $X$, and every uniform basis is Schauder. Regarding Banach spaces, we address two problems concerning filter Schauder bases for Banach spaces, i.e., in which the norm convergence of partial sums is replaced by norm convergence along some appropriate filter on $\mathbb{N}$. We first provide an example of a Banach space admitting such a filter Schauder basis, but no ordinary Schauder basis. Secondly, we show that every filter Schauder basis with respect to an analytic filter is also a filter Schauder basis with respect to a Borel filter.

Keywords: Order bases; Schauder bases; Filter bases; Projective determinacy.

@Techreport{ARTT24_1102,
  author = {A. Aviles and C. Rosendal and M. Taylor and P. Tradacete},
  title = {Coordinate systems in Banach spaces and lattices},
  institution = {Seminar for Applied Mathematics, ETH Z{\"u}rich},
  number = {2024-20},
  address = {Switzerland},
  url = {https://www.sam.math.ethz.ch/sam_reports/reports_final/reports2024/2024-20.pdf },
  year = {2024}
}

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