English

A note on a new ideal

Combinatorics 2017-09-26 v3

Abstract

In this paper we study a new ideal WR\mathcal{WR}. The main result is the following: an ideal is not weakly Ramsey if and only if it is above WR\mathcal{WR} in the Kat\v{e}tov order. Weak Ramseyness was introduced by Laflamme in order to characterize winning strategies in a certain game. We apply result of Natkaniec and Szuca to conclude that WR\mathcal{WR} is critical for ideal convergence of sequences of quasi-continuous functions. We study further combinatorial properties of WR\mathcal{WR} and weak Ramseyness. Answering a question of Filip\'ow et al. we show that WR\mathcal{WR} is not 22-Ramsey, but every ideal on ω\omega isomorphic to WR\mathcal{WR} is Mon (every sequence of reals contains a monotone subsequence indexed by a I\mathcal{I}-positive set).

Keywords

Cite

@article{arxiv.1409.8335,
  title  = {A note on a new ideal},
  author = {Adam Kwela},
  journal= {arXiv preprint arXiv:1409.8335},
  year   = {2017}
}
R2 v1 2026-06-22T06:08:53.851Z