English

$\mathbb{M}^*$, $\mathbb{N}^*$, and $\mathbb{H}^*$

General Topology 2025-08-12 v1 Logic

Abstract

Let M=N×[0,1]\mathbb{M} = \mathbb N \times [0,1]. The natural projection π:MN\pi: \mathbb{M} \rightarrow \mathbb N, which sends (n,x)(n,x) to nn, induces a projection mapping π:MN\pi^*: \mathbb{M}^* \rightarrow \mathbb N^*, where M\mathbb{M}^* and N\mathbb N^* denote the \v{C}ech-Stone remainders of M\mathbb{M} and N\mathbb N, respectively. We show that CH\mathsf{CH} implies every autohomeomorphism of N\mathbb N^* lifts through the natural projection to an autohomeomorphism of M\mathbb{M}^*. That is, for every homeomorphism h:NNh: \mathbb N^* \rightarrow \mathbb N^* there is a homeomorphism H:MMH: \mathbb{M}^* \rightarrow \mathbb{M}^* such that πH=hπ\pi^* \circ H = h \circ \pi^*. This complements a recent result of the second author, who showed that this lifting property is not a consequence of ZFC\mathsf{ZFC}. Combining this lifting theorem with a recent result of the first author, we also prove that CH\mathsf{CH} implies there is an order-reversing autohomeomorphism of~H\mathbb H^*, the \v{C}ech-Stone remainder of the half line H=[0,)\mathbb H = [0,\infty).

Cite

@article{arxiv.2505.04425,
  title  = {$\mathbb{M}^*$, $\mathbb{N}^*$, and $\mathbb{H}^*$},
  author = {Will Brian and Alan Dow and Klaas Pieter Hart},
  journal= {arXiv preprint arXiv:2505.04425},
  year   = {2025}
}
R2 v1 2026-06-28T23:24:30.085Z