English

Sets of Ramsey-limit points and IP-limit points

General Topology 2026-01-21 v1 Dynamical Systems Logic

Abstract

Let XX be an uncountable Polish space and let H\mathcal{H} be the Hindman ideal, that is, the family of all SωS\subseteq \omega which are not IPIP-sets. For each sequence x=(xn)nωx=(x_n)_{n \in \omega} taking values in XX, let Λx(FS)\Lambda_{x}(FS) be the set of IPIP-limit points of xx. Also, let Λx(H)\Lambda_{x}(\mathcal{H}) be the set of H\mathcal{H}-limit points of xx, that is, the set of ordinary limits of subsequences (xn)nS(x_n)_{n \in S} with SHS\notin \mathcal{H}. After proving that these two notions do not coincide in general, we show that both families of nonempty sets of the type Λx(FS)\Lambda_{x}(FS) and of the type Λx(H)\Lambda_{x}(\mathcal{H}) are precisely the class of nonempty analytic subsets of XX. An analogous result holds also for Ramsey convergence. In the proofs, we use the concept of partition regular functions introduced in J. Symb. Log. (2024) [doi:10.1017/jsl.2024.8], which provide a unified approach to these types of convergence.

Keywords

Cite

@article{arxiv.2601.12187,
  title  = {Sets of Ramsey-limit points and IP-limit points},
  author = {Rafał Filipów and Adam Kwela and Paolo Leonetti},
  journal= {arXiv preprint arXiv:2601.12187},
  year   = {2026}
}