English

A note on images of cover relations

Category Theory 2020-11-16 v1

Abstract

For a category C\mathbb{C}, a small category I\mathbb{I}, and a pre-cover relation \sqsubset on C\mathbb C we prove, under certain completeness assumptions on C\mathbb C, that a morphism g:BCg: B\to C in the functor category CI\mathbb {C}^{\mathbb I} admits an image with respect to the pre-cover relation on CI\mathbb C^{\mathbb I} induced by \sqsubset as soon as each component of gg admits an image with respect to \sqsubset. We then apply this to show that if a pointed category C\mathbb{C} is: (i) algebraically cartesian closed; (ii) exact protomodular and action accessible; or (iii) admits normalizers, then the same is true of each functor category CI\mathbb{C}^{\mathbb I} with I\mathbb{I} finite. In addition, our results give explicit constructions of images in functor categories using limits and images in the underlying category. In particular, they can be used to give explicit constructions of both centralizers and normalizers in functor categories using limits and centralizers or normalizers (respectively) in the underlying category.

Keywords

Cite

@article{arxiv.2011.06903,
  title  = {A note on images of cover relations},
  author = {James Richard Andrew Gray},
  journal= {arXiv preprint arXiv:2011.06903},
  year   = {2020}
}