English

Banach spaces of $\mathcal I$-convergent sequences

Functional Analysis 2023-09-18 v1

Abstract

We study the space c0,Ic_{0,\mathcal{I}} of all bounded sequences (xn)(x_n) that I\mathcal{I}-converge to 00, endowed with the sup norm, where I\mathcal{I} is an ideal of subsets of N\mathbb{N}. We show that two such spaces, c0,Ic_{0,\mathcal{I}} and c0,Jc_{0,\mathcal{J}}, are isometric exactly when the ideals I\mathcal{I} and J\mathcal{J} are isomorphic. Additionally, we analyze the connection of the well-known Kat\v{e}tov pre-order K\leq_K on ideals with some properties of the space c0,Ic_{0,\mathcal{I}}. For instance, we show that IKJ\mathcal{I}\leq_K\mathcal{J} exactly when there is a (not necessarily onto) Banach lattice isometry from c0,Ic_{0,\mathcal{I}} to c0,Jc_{0,\mathcal{J}}, satisfying some additional conditions. We present some lattice-theoretic properties of c0,Ic_{0,\mathcal{I}}, particularly demonstrating that every closed ideal of \ell_\infty is equal to c0,Ic_{0,\mathcal{I}} for some ideal I\mathcal{I} on N\mathbb{N}. We also show that certain classical Banach spaces are isometric to c0,Ic_{0,\mathcal{I}} for some ideal I\mathcal{I}, such as the spaces (c0)\ell_\infty(c_0) and c0()c_0(\ell_\infty). Finally, we provide several examples of ideals for which c0,Ic_{0,\mathcal{I}} is not a Grothendieck space.

Keywords

Cite

@article{arxiv.2309.08076,
  title  = {Banach spaces of $\mathcal I$-convergent sequences},
  author = {Michael A. Rincón-Villamizar and Carlos Uzcátegui Aylwin},
  journal= {arXiv preprint arXiv:2309.08076},
  year   = {2023}
}
R2 v1 2026-06-28T12:22:10.208Z