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[Merged by Bors] - feat(category_theory/monoidal): Drinfeld center #7186

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@semorrison semorrison commented Apr 14, 2021

Half braidings and the Drinfeld center of a monoidal category

We define center C to be pairs ⟨X, b⟩, where X : C and b is a half-braiding on X.

We show that center C is braided monoidal,
and provide the monoidal functor center.forget from center C back to C.

Future work

Verifying the various axioms here is done by tedious rewriting.
Using the slice tactic may make the proofs marginally more readable.

More exciting, however, would be to make possible one of the following options:

  1. Integration with homotopy.io / globular to give "picture proofs".
  2. The monoidal coherence theorem, so we can ignore associators
    (after which most of these proofs are trivial;
    I'm unsure if the monoidal coherence theorem is even usable in dependent type theory).
  3. Automating these proofs using rewrite_search or some relative.

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@semorrison semorrison added awaiting-review The author would like community review of the PR and removed WIP Work in progress labels Apr 17, 2021
@semorrison semorrison marked this pull request as ready for review April 17, 2021 02:47
@semorrison semorrison changed the title wip(category_theory/monoidal): Drinfeld center feat(category_theory/monoidal): Drinfeld center Apr 17, 2021
@semorrison semorrison requested a review from b-mehta April 17, 2021 11:19
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I shortened some of the proofs, I still think they're not the shortest path but they might be closer!

src/category_theory/monoidal/center.lean Outdated Show resolved Hide resolved
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I shortened some of the proofs, I still think they're not the shortest path but they might be closer!

Your shortened proofs are still not "pure rewriting proofs", in the sense that that they rewrite by cancellation lemmas which operate on both sides at once. But I don't object. :-)

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Thanks 🎉

bors merge

@github-actions github-actions bot added ready-to-merge All that is left is for bors to build and merge this PR. (Remember you need to say `bors r+`.) and removed awaiting-review The author would like community review of the PR labels Apr 20, 2021
bors bot pushed a commit that referenced this pull request Apr 21, 2021
# Half braidings and the Drinfeld center of a monoidal category

We define `center C` to be pairs `⟨X, b⟩`, where `X : C` and `b` is a half-braiding on `X`.

We show that `center C` is braided monoidal,
and provide the monoidal functor `center.forget` from `center C` back to `C`.

## Future work

Verifying the various axioms here is done by tedious rewriting.
Using the `slice` tactic may make the proofs marginally more readable.

More exciting, however, would be to make possible one of the following options:
1. Integration with homotopy.io / globular to give "picture proofs".
2. The monoidal coherence theorem, so we can ignore associators
   (after which most of these proofs are trivial;
   I'm unsure if the monoidal coherence theorem is even usable in dependent type theory).
3. Automating these proofs using `rewrite_search` or some relative.



Co-authored-by: Scott Morrison <scott.morrison@gmail.com>
Co-authored-by: Bhavik Mehta <bhavikmehta8@gmail.com>
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bors bot commented Apr 21, 2021

Pull request successfully merged into master.

Build succeeded:

@bors bors bot changed the title feat(category_theory/monoidal): Drinfeld center [Merged by Bors] - feat(category_theory/monoidal): Drinfeld center Apr 21, 2021
@bors bors bot closed this Apr 21, 2021
@bors bors bot deleted the drinfeld_2 branch April 21, 2021 09:01
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