English

Simultaneously vanishing higher derived limits

Logic 2021-07-01 v3 Algebraic Topology

Abstract

In 1988, Sibe Marde\v{s}i\'{c} and Andrei Prasolov isolated an inverse system A\mathbf{A} with the property that the additivity of strong homology on any class of spaces which includes the closed subsets of Euclidean space would entail that limnA\lim^n\mathbf{A} (the nthn^{\text{th}} derived limit of A\mathbf{A}) vanishes for every n>0n >0. Since that time, the question of whether it is consistent with the ZFC\mathsf{ZFC} axioms that limnA=0\lim^n \mathbf{A}=0 for every n>0n >0 has remained open. It remains possible as well that this condition in fact implies that strong homology is additive on the category of metric spaces. We show that, assuming the existence of a weakly compact cardinal, it is indeed consistent with the ZFC\mathsf{ZFC} axioms that limnA=0\lim^n \mathbf{A}=0 for all n>0n >0. We show this via a finite support iteration of Hechler forcings which is of weakly compact length. More precisely, we show that in any forcing extension by this iteration a condition equivalent to limnA=0\lim^n\mathbf{A}=0 will hold for each n>0n>0. This condition is of interest in its own right; namely, it is the triviality of every coherent nn-dimensional family of certain specified sorts of partial functions N2Z\mathbb{N}^2\to\mathbb{Z} which are indexed in turn by nn-tuples of functions f:NNf:\mathbb{N}\to\mathbb{N}. The triviality and coherence in question here generalize the well-studied case of n=1n=1.

Keywords

Cite

@article{arxiv.1907.11744,
  title  = {Simultaneously vanishing higher derived limits},
  author = {Jeffrey Bergfalk and Chris Lambie-Hanson},
  journal= {arXiv preprint arXiv:1907.11744},
  year   = {2021}
}

Comments

35 pages. Accepted to Forum of Mathematics: Pi

R2 v1 2026-06-23T10:32:20.397Z