English

On good morphisms of exact triangles

Algebraic Topology 2023-01-10 v3 Category Theory

Abstract

In a triangulated category, cofibre fill-ins always exist. Neeman showed that there is always at least one "good" fill-in, i.e., one whose mapping cone is exact. Verdier constructed a fill-in of a particular form in his proof of the 4×44 \times 4 lemma, which we call "Verdier good". We show that for several classes of morphisms of exact triangles, the notions of good and Verdier good agree. We prove a lifting criterion for commutative squares in terms of (Verdier) good fill-ins. Using our results on good fill-ins, we also prove a pasting lemma for homotopy cartesian squares.

Keywords

Cite

@article{arxiv.2008.03643,
  title  = {On good morphisms of exact triangles},
  author = {J. Daniel Christensen and Martin Frankland},
  journal= {arXiv preprint arXiv:2008.03643},
  year   = {2023}
}

Comments

v3: Minor changes. Accepted for publication in the Journal of Pure and Applied Algebra

R2 v1 2026-06-23T17:43:39.692Z