English

Non-vanishing higher derived limits

Logic 2021-07-09 v1 Category Theory

Abstract

In the study of strong homology Marde\v{s}i\'c and Prasolov isolated a certain inverse system of abelian groups A\mathbf A indexed by elements of ωω\omega^\omega. They showed that if strong homology is additive on a class of spaces containing closed subsets of Euclidean spaces then the higher derived limits limnA\lim^n \mathbf A must vanish, for n>0n>0. They also proved that under the Continuum Hypothesis lim1A0\lim^1 \mathbf A \neq 0. The question whether limnA\lim^n \mathbf A vanishes, for n>0n>0, has attracted considerable interest from set theorists. Dow, Simon and Vaughan showed that under PFA lim1A=0\lim^1 \mathbf A =0. Bergfalk show that it is consistent that lim2A\lim^2\mathbf A does not vanish. Later Bergfalk and Lambie-Hanson showed that, modulo a weakly compact cardinal, it is relatively consistent with ZFC that limnA=0\lim^n \mathbf A =0, for all nn. The large cardinal assumption was recently removed by Bergfalk, Hru\v{s}ak and Lambie-Henson. We complete the picture by showing that, for any n>0n>0, it is relatively consistent with ZFC that limnA0\lim^n \mathbf A \neq 0.

Keywords

Cite

@article{arxiv.2107.03787,
  title  = {Non-vanishing higher derived limits},
  author = {Boban Velickovic and Alessandro Vignati},
  journal= {arXiv preprint arXiv:2107.03787},
  year   = {2021}
}
R2 v1 2026-06-24T03:59:51.886Z