Diamond on ladder systems and countably metacompact topological spaces

Joint work with Rodrigo Rey Carvalho and Tanmay Inamdar.

Abstract. Leiderman and Szeptycki proved that a single Cohen real introduces a ladder system L over 1 for which the space XL is not a Δ-space. They asked whether there is a ZFC example of a ladder system L over some cardinal κ for which XL is not countably metacompact, in particular, not a Δ-space.  We prove that an affirmative answer holds for κ=cf(ω+1). This is an application of a theorem of Shelah concerning diamond on ladder systems, and we include a streamlined presentation of this result. Assuming ω=ω, we get an example at a much lower cardinal, namely κ=2220, and our ladder system L is moreover ω-bounded.

Downloads:

[No entry on mathscinet]

 

This entry was posted in Preprints, Topology and tagged , , , , , , , , . Bookmark the permalink.

3 Responses to Diamond on ladder systems and countably metacompact topological spaces

  1. saf says:

    Update January 2024: Added a section “Club guessing with diamonds”, where we address the case of omega-bounded ladder systems.

  2. saf says:

    Submitted to Journal of Symbolic Logic, December 2023.
    Accepted, May 2024.

  3. saf says:

    Update July 2024: Corrected Footnote #1. It used to say “for every lambda” and now says “for class many lambda’s”.

Comments are closed.