English

Talagrand compacta, 2DCP, and pointwise quotients

General Topology 2026-07-07 v1

Abstract

We revisit Talagrand's CH compactum as a test object for the two-disjoint-copies property and for pointwise quotient questions. The two-disjoint-copies property, or 2DCP, is a topological sufficient condition for the existence of infinite-dimensional metrisable quotients of spaces Cp(X)C_{\operatorname{p}}(X); recent work asks whether Talagrand's compactum has this property. Assuming (S)\diamondsuit(S) for a stationary co-stationary Sω1S\subseteq\omega_1, we carry out Talagrand's inverse-limit construction with additional diagonalisation. The resulting compactum TT keeps Talagrand's conclusions: C(T)C(T) is Grothendieck, the weak-star compact ball M1(T)M_1(T) contains no copy of βω\beta\omega, and TT has no non-trivial convergent sequences. At the same time, no two disjoint non-metrisable closed subspaces of TT are homeomorphic; hence TT has no 2DCP and is not locally homogeneous. We also give a ZFC example of a perfect compact space with 2DCP which is not locally homogeneous and contains neither βω\beta\omega nor 2ω2^\omega. Finally, we isolate a general locally convex observation, in the spirit of the Banakh--Gabriyelyan theory of the Josefson--Nissenzweig property, showing that pointwise quotients onto (p)p(\ell_p)_{\operatorname{p}}, 1p<1\leqslant p<\infty, force the Josefson--Nissenzweig property. Consequently Talagrand compacta have no classical pointwise sequence quotients (c0)p(c_0)_{\operatorname{p}}, (p)p(\ell_p)_{\operatorname{p}}, or ()p(\ell_\infty)_{\operatorname{p}}. The full metrisable quotient problem for these CpC_{\operatorname{p}}-spaces remains open. Several open problems are included.

Cite

@article{arxiv.2607.06808,
  title  = {Talagrand compacta, 2DCP, and pointwise quotients},
  author = {Tomasz Kania and Jerzy Kąkol},
  journal= {arXiv preprint arXiv:2607.06808},
  year   = {2026}
}

Comments

19 pp