English

Continuum Without Non-Block Points

General Topology 2020-07-21 v1

Abstract

For any composant EHE \subset \mathbb H^* and corresponding near-coherence class Eω\mathscr E \subset \omega^* we prove the following are equivalent : (1) EE properly contains a dense semicontinuum. (2) Each countable subset of EE is contained in a dense proper semicontinuum of EE. (3) Each countable subset of EE is disjoint from some dense proper semicontinuum of EE. (4) E\mathscr E has a minimal element in the finite-to-one monotone order of ultrafilters. (5) E\mathscr E has a QQ-point. A consequence is that NCF is equivalent to H\mathbb H^* containing no proper dense semicontinuum and no non-block points. This gives an axiom-contingent answer to a question of the author. Thus every known continuum has either a proper dense semicontinuum at every point or at no points. We examine the structure of indecomposable continua for which this fails, and deduce they contain a maximum semicontinuum with dense interior.

Keywords

Cite

@article{arxiv.2007.09168,
  title  = {Continuum Without Non-Block Points},
  author = {Daron Anderson},
  journal= {arXiv preprint arXiv:2007.09168},
  year   = {2020}
}
R2 v1 2026-06-23T17:12:19.573Z