English

Anticommutativity and the triangular lemma

Category Theory 2020-11-03 v2

Abstract

For a variety V\mathcal{V}, it has been recently shown that binary products commute with arbitrary coequalizers locally, i.e., in every fibre of the fibration of points π:Pt(C)C\pi: \mathrm{Pt} (\mathbb{C}) \rightarrow \mathbb{C}, if and only if Gumm's shifting lemma holds on pullbacks in V\mathcal{V}. In this paper, we establish a similar result connecting the so-called triangular lemma in universal algebra with a certain categorical anticommutativity\textit{anticommutativity} condition. In particular, we show that this anticommutativity and its local version are Mal'tsev conditions, the local version being equivalent to the triangular lemma on pullbacks. As a corollary, every locally anticommutative variety V\mathcal{V} has directly decomposable congruence classes in the sense of Duda, and the converse holds if V\mathcal{V} is idempotent.

Keywords

Cite

@article{arxiv.2008.00486,
  title  = {Anticommutativity and the triangular lemma},
  author = {Michael Hoefnagel},
  journal= {arXiv preprint arXiv:2008.00486},
  year   = {2020}
}

Comments

18 pages

R2 v1 2026-06-23T17:35:06.821Z