English

The oplax limit of an enriched category

Category Theory 2024-05-24 v2

Abstract

We show that 2-categories of the form B\mboxCat\mathscr{B}\mbox{-}\mathbf{Cat} are closed under slicing, provided that we allow B\mathscr{B} to range over bicategories (rather than, say, monoidal categories). That is, for any B\mathscr{B}-category X\mathbb{X}, we define a bicategory B/X\mathscr{B}/\mathbb{X} such that B\mboxCat/X(B/X)\mboxCat\mathscr{B}\mbox{-}\mathbf{Cat}/\mathbb{X}\cong (\mathscr{B}/\mathbb{X})\mbox{-}\mathbf{Cat}. The bicategory B/X\mathscr{B}/\mathbb{X} is characterized as the oplax limit of X\mathbb{X}, regarded as a lax functor from a chaotic category to B\mathscr{B}, in the 2-category BICAT\mathbf{BICAT} of bicategories, lax functors and icons. We prove this conceptually, through limit-preservation properties of the 2-functor BICAT2\mboxCAT\mathbf{BICAT}\to 2\mbox{-}\mathbf{CAT} which maps each bicategory B\mathscr{B} to the 2-category B\mboxCat\mathscr{B}\mbox{-}\mathbf{Cat}. When B\mathscr{B} satisfies a mild local completeness condition, we also show that the isomorphism B\mboxCat/X(B/X)\mboxCat\mathscr{B}\mbox{-}\mathbf{Cat}/\mathbb{X}\cong (\mathscr{B}/\mathbb{X})\mbox{-}\mathbf{Cat} restricts to a correspondence between fibrations in B\mboxCat\mathscr{B}\mbox{-}\mathbf{Cat} over X\mathbb{X} on the one hand, and B/X\mathscr{B}/\mathbb{X}-categories admitting certain powers on the other.

Keywords

Cite

@article{arxiv.2211.12122,
  title  = {The oplax limit of an enriched category},
  author = {Soichiro Fujii and Stephen Lack},
  journal= {arXiv preprint arXiv:2211.12122},
  year   = {2024}
}

Comments

22 pages, final journal version