English

Connectedness modulo an ideal

General Topology 2016-11-04 v2

Abstract

For a topological space XX and an ideal H\mathscr{H} of subsets of XX we introduce the notion of connectedness modulo H\mathscr{H}. This notion of connectedness naturally generalizes the notion of connectedness in its usual sense. In the case when XX is completely regular, we introduce a subspace γHX\gamma_{\mathscr H} X of the Stone--\v{C}ech compactification βX\beta X of XX, such that connectedness modulo H{\mathscr H} is equivalent to connectedness of βXγHX\beta X\setminus\gamma_{\mathscr H} X. In particular, we prove that when H{\mathscr H} is the ideal generated by the collection of all open subspaces of XX with pseudocompact closure, then XX is connected modulo H{\mathscr H} if and only if clβX(βXυX)\mathrm{cl}_{\beta X}(\beta X\setminus\upsilon X) is connected, and when XX is normal and H{\mathscr H} is the ideal generated by the collection of all closed realcompact subspaces of XX, then XX is connected modulo H{\mathscr H} if and only if clβX(υXX)\mathrm{cl}_{\beta X}(\upsilon X\setminus X) is connected. Here υX\upsilon X is the Hewitt realcompactification of XX.

Keywords

Cite

@article{arxiv.1411.0908,
  title  = {Connectedness modulo an ideal},
  author = {M. R. Koushesh},
  journal= {arXiv preprint arXiv:1411.0908},
  year   = {2016}
}

Comments

28 pages

R2 v1 2026-06-22T06:47:35.039Z