English

Representations of ideals in Polish groups and in Banach spaces

Logic 2014-02-04 v1

Abstract

We investigate ideals of the form {Aω ⁣:nAxn\{A \subseteq \omega\colon \sum_{n\in A} x_n is unconditionally convergent }\}, where (xn)nω(x_n)_{n\in\omega} is a sequence in a Polish group or in a Banach space. If an ideal on ω\omega can be seen in this form for some sequence in XX, then we say that it is representable in XX. After numerous examples we show the following theorems: (1) An ideal is representable in a Polish Abelian group iff it is an analytic P-ideal. (2) An ideal is representable in a Banach space iff it is a non-pathological analytic P-ideal. We focus on the family of ideals representable in c0c_0. We prove that the trace of the null ideal, Farah's ideal, and Tsirelson ideals are not representable in c0c_0, and that a tall FσF_\sigma P-ideal is representable in c0c_0 iff it is a summable ideal. Also, we provide an example of a peculiar ideal which is representable in 1\ell_1 but not in R\mathbb{R}. Finally, we summarize some open problems of this topic.

Keywords

Cite

@article{arxiv.1402.0441,
  title  = {Representations of ideals in Polish groups and in Banach spaces},
  author = {Piotr Borodulin-Nadzieja and Barnabas Farkas and Grzegorz Plebanek},
  journal= {arXiv preprint arXiv:1402.0441},
  year   = {2014}
}