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Comonoids, duality, and related displayed tech#584

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jajaperson wants to merge 18 commits intothe1lab:mainfrom
jajaperson:monoidal-internalization
Draft

Comonoids, duality, and related displayed tech#584
jajaperson wants to merge 18 commits intothe1lab:mainfrom
jajaperson:monoidal-internalization

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@jajaperson
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@jajaperson jajaperson commented Jan 16, 2026

WIP

Description

This PR is working up to proving $\mathrm{Mon}(\mathcal C^\mathrm{op})^\mathrm{op}$ and $\mathrm{Comon}(\mathcal C)$ are equivalent as displayed categories. This has involved defining a lot of displayed machinery.

  • Comonoids
  • Total functor of displayed functor
  • Total natural transformation of displayed NT
  • Total adjunction of displayed adjunction
  • Sigma displayed category from Ahrens and Lumsdaine (2017)1 just for fun
  • Displayed category of displayed functors
  • Displayed equivalence
  • Total equivalence of displayed equivalence
  • Displayed equivalence of $\mathrm{Mon}(\mathcal C^\mathrm{op})^\mathrm{op}$ and $\mathrm{Comon}(\mathcal C)$

Checklist

Before submitting a merge request, please check the items below:

  • I've read the contributing guidelines.
  • The imports of new modules have been sorted with support/sort-imports.hs (or nix run --experimental-features nix-command -f . sort-imports).
  • All new code blocks have "agda" as their language.

If your change affects many files without adding substantial content, and
you don't want your name to appear on those pages (for example, treewide
refactorings or reformattings), start the commit message and PR title with chore:.

Footnotes

  1. Ahrens, Benedikt, and Peter LeFanu Lumsdaine. 2017. “Displayed Categories.” In 2nd International Conference on Formal Structures for Computation and Deduction (FSCD 2017), edited by Dale Miller, vol. 84. Leibniz International Proceedings in Informatics (LIPIcs). Schloss Dagstuhl – Leibniz-Zentrum für Informatik. https://doi.org/10.4230/LIPIcs.FSCD.2017.5.

@Lavenza
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Lavenza commented Jan 16, 2026

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2 participants