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[Merged by Bors] - feat(CategoryTheory): the left lifting property is stable under transfinite composition#20119

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[Merged by Bors] - feat(CategoryTheory): the left lifting property is stable under transfinite composition#20119
joelriou wants to merge 13 commits intomasterfrom
well-order-continuous-lifting

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@joelriou joelriou commented Dec 20, 2024 •
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After #19135 is merged, it will be possible to phrase this in terms of MorphismProperty.llp and get better looking statements.

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@joelriou joelriou added the t-category-theory Category theory label Dec 20, 2024
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PR summary 3a62eef02c

Import changes for modified files

No significant changes to the import graph

Import changes for all files
Files Import difference
Mathlib.CategoryTheory.SmallObject.TransfiniteCompositionLifting (new file) 530

Declarations diff

+ SqStruct
+ hasLift
+ hasLiftingProperty_ι_app_bot
+ lift
+ liftHom
+ liftHom_fac
+ map
+ map_lift
+ sq
+ sqFunctor
+ w
+ wellOrderInductionData

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

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

The doc-module for script/declarations_diff.sh contains some details about this script.

No changes to technical debt.

You can run this locally as

./scripts/technical-debt-metrics.sh pr_summary
  • The relative value is the weighted sum of the differences with weight given by the inverse of the current value of the statistic.
  • The absolute value is the relative value divided by the total sum of the inverses of the current values (i.e. the weighted average of the differences).

@joelriou joelriou changed the title feat(CategoryTheory): the left lifting property is stable by transfinite compositions feat(CategoryTheory): the left lifting property is stable under transfinite composition Dec 20, 2024
jcommelin
jcommelin reviewed Dec 20, 2024
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bors d+

Mathlib/CategoryTheory/SmallObject/TransfiniteCompositionLifting.lean Outdated
Comment on lines +43 to +48
/-- Given a colimit cocone `c` for a functor `F : J ⥤ C` from a well-ordered type,
and maps `p : X ⟶ Y`, `f : F.obj ⊥ ⟶ X`, `g : c.pt ⟶ Y`, this structure
contains the data of a map `F.obj j ⟶ X` such that `F.map (homOfLE bot_le) ≫ f' = f`
and `f' ≫ p = c.ι.app j ≫ g`. -/
@[ext]
structure SqStruct (j : J) where
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Could you please motivate the name, maybe by drawing an ascii-art diagram in the docstring?

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Thanks for the suggestion! I have added a comment about the general strategy of the proof and some asciiart.

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mathlib-bors bot commented Dec 20, 2024

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

@ghost ghost added the delegated This pull request has been delegated to the PR author (or occasionally another non-maintainer). label Dec 20, 2024
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joelriou commented Dec 20, 2024

Thanks!

bors merge

@ghost ghost added the ready-to-merge This PR has been sent to bors. label Dec 20, 2024
mathlib-bors bot pushed a commit that referenced this pull request Dec 20, 2024
@joelriou
feat(CategoryTheory): the left lifting property is stable under trans…
7f72da4 
…finite composition (#20119)

After #19135 is merged, it will be possible to phrase this in terms of `MorphismProperty.llp` and get better looking statements.



Co-authored-by: Joël Riou <37772949+joelriou@users.noreply.github.com>
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mathlib-bors bot commented Dec 20, 2024

Pull request successfully merged into master.

Build succeeded:

@mathlib-bors mathlib-bors bot changed the title feat(CategoryTheory): the left lifting property is stable under transfinite composition [Merged by Bors] - feat(CategoryTheory): the left lifting property is stable under transfinite composition Dec 20, 2024
@mathlib-bors mathlib-bors bot closed this Dec 20, 2024
@mathlib-bors mathlib-bors bot deleted the well-order-continuous-lifting branch December 20, 2024 17:17
@joelriou joelriou mentioned this pull request Feb 10, 2025
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mathlib-bors bot pushed a commit that referenced this pull request Feb 11, 2025
@joelriou
feat(CategoryTheory/SmallObject): llp is stable under transfinite com…
66c4d09 
…position (#21682)

We deduce from previous results (#20119) that if `W : MorphismProperty C`, then the class `W.llp` of morphisms which satisfy the left lifting property with respect to `W` is stable under transfinite composition.
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