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[Merged by Bors] - feat(CategoryTheory): if LR is abstractly isomorphic to the identity functor, then the unit is an isomorphism.#14017

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[Merged by Bors] - feat(CategoryTheory): if LR is abstractly isomorphic to the identity functor, then the unit is an isomorphism.#14017
dagurtomas wants to merge 5 commits intomasterfrom
dagur/MagicAdjunctionLemma

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@dagurtomas dagurtomas commented Jun 21, 2024

This PR proves that to show that the unit of an adjunction L ⊣ R is an isomorphism (i.e. that L is fully faithful), it is enough to give an arbitrary isomorphism L ⋙ R ≅ 𝟭 C, and the dual result.

To do this, we give a general way to transport (co)monad structures on functors along isomorphisms of functors.


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github-actions bot commented Jun 21, 2024

PR summary 1993861f07

Import changes

No significant changes to the import graph


Declarations diff

+ counitAsIsoOfIso
+ fullyFaithfulLOfCompIsoId
+ fullyFaithfulROfCompIsoId
+ id_comm
+ isIso_counit_of_iso
+ isIso_unit_of_iso
+ unitAsIsoOfIso
++ transport

You can run this locally as follows
## summary with just the declaration names:
./scripts/no_lost_declarations.sh short <optional_commit>

## more verbose report:
./scripts/no_lost_declarations.sh <optional_commit>

Given an adjunction `L ⊣ R`, if `L ⋙ R` is abstractly isomorphic to the identity functor, then the
unit is an isomorphism.
-/
def unitAsIsoOfAbstractIso (adj : L ⊣ R) (i : L ⋙ R ≅ 𝟭 C) : 𝟭 C ≅ L ⋙ R where
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Let's remove Abstract from the name, here and below, so just unitAsIsoOfIso.

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kim-em commented Jul 1, 2024

bors d+

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mathlib-bors bot commented Jul 1, 2024

✌️ dagurtomas can now approve this pull request. To approve and merge a pull request, simply reply with bors r+. More detailed instructions are available here.

@github-actions github-actions bot added delegated This pull request has been delegated to the PR author (or occasionally another non-maintainer). and removed awaiting-review labels Jul 1, 2024
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Thanks for the reviews!

bors merge

mathlib-bors bot pushed a commit that referenced this pull request Jul 1, 2024
…functor, then the unit is an isomorphism. (#14017)

This PR proves that to show that the unit of an adjunction `L ⊣ R` is an isomorphism (i.e. that L is fully faithful), it is enough to give an arbitrary isomorphism `L ⋙ R ≅ 𝟭 C`, and the dual result. 

To do this, we give a general way to transport (co)monad structures on functors along isomorphisms of functors.
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mathlib-bors bot commented Jul 1, 2024

Build failed (retrying...):

mathlib-bors bot pushed a commit that referenced this pull request Jul 1, 2024
…functor, then the unit is an isomorphism. (#14017)

This PR proves that to show that the unit of an adjunction `L ⊣ R` is an isomorphism (i.e. that L is fully faithful), it is enough to give an arbitrary isomorphism `L ⋙ R ≅ 𝟭 C`, and the dual result. 

To do this, we give a general way to transport (co)monad structures on functors along isomorphisms of functors.
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mathlib-bors bot commented Jul 1, 2024

Pull request successfully merged into master.

Build succeeded:

@mathlib-bors mathlib-bors bot changed the title feat(CategoryTheory): if LR is abstractly isomorphic to the identity functor, then the unit is an isomorphism. [Merged by Bors] - feat(CategoryTheory): if LR is abstractly isomorphic to the identity functor, then the unit is an isomorphism. Jul 1, 2024
@mathlib-bors mathlib-bors bot closed this Jul 1, 2024
dagurtomas added a commit that referenced this pull request Jul 2, 2024
…functor, then the unit is an isomorphism. (#14017)

This PR proves that to show that the unit of an adjunction `L ⊣ R` is an isomorphism (i.e. that L is fully faithful), it is enough to give an arbitrary isomorphism `L ⋙ R ≅ 𝟭 C`, and the dual result. 

To do this, we give a general way to transport (co)monad structures on functors along isomorphisms of functors.
@adomani adomani mentioned this pull request Aug 1, 2024
@YaelDillies YaelDillies deleted the dagur/MagicAdjunctionLemma branch August 15, 2025 16:29
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3 participants