English

The Shore Point Existence Problem is Equivalent to the Non-Block Point Existence Problem

General Topology 2020-07-21 v1

Abstract

We prove the three propositions are equivalent: (a)(a) Every Hausdorff continuum has two or more shore points. (b)(b) Every Hausdorff continuum has two or more non-block points. (c)(c) Every Hausdorff continuum is coastal at each point. Thus it is consistent that all three properties fail. We also give the following characterisation of shore points: The point pp of the continuum XX is a shore point if and only if there is a net of subcontinua in {KC(X):Kκ(p)p}\{K \in C(X): K \subset \kappa(p) - p\} tending to XX in the Vietoris topology. This contrasts with the standard characterisation which only demands the net elements be contained in XpX-p. In addition we prove every point of an indecomposable continuum is a shore point.

Cite

@article{arxiv.2007.09234,
  title  = {The Shore Point Existence Problem is Equivalent to the Non-Block Point Existence Problem},
  author = {Daron Anderson},
  journal= {arXiv preprint arXiv:2007.09234},
  year   = {2020}
}
R2 v1 2026-06-23T17:12:29.559Z