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feat(combinatorics/quiver): isomorphisms of quivers #18511

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@bottine bottine commented Feb 28, 2023

Co-authored-by: Adam Topaz [email protected]


The of_bijective part has been kindly provided by @adamtopaz, can I add a co-authored-by line?

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@bottine bottine requested a review from a team as a code owner February 28, 2023 07:56
@bottine bottine added awaiting-review The author would like community review of the PR t-combinatorics Combinatorics labels Feb 28, 2023
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alreadydone commented Feb 28, 2023

The of_bijective part has been kindly provided by @adamtopaz, can I add a co-authored-by line?

Yeah I think that's common practice.

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bottine commented Feb 28, 2023

Thanks, I'm sometimes reluctant to do it in instances (like this one) where I asked for help and got a ready-to-use piece of code: the co-authored-by line could signal explicit co-authorship, when I just took the code and the other person didn't have a say in the result. I'm not sure that makes sense?

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I think the main point of the "co-authored-by" lines is that they go into the commit message and are collected into stats like the Authors table here.

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Can you show that an equivalence of categories is an isomorphism of quivers?

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bottine commented Mar 1, 2023

No, since an equivalence is just "essentially surjective on objects" while an isomorphism of quivers is bijective on objects (afaiu).

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bottine commented Mar 1, 2023

Can you show that an equivalence of categories is an isomorphism of quivers?

But on that subject, I don't know to what extent I should try and build conversions between all this quiver stuff and categories.
I guess if the quiver stuff had been defined early on, some categorical notions could have been defined on top of that, but since they already exist by now, and the applications for me are mainly "graph-theoretical", there is not necessarily much point to bridge the two?

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The simple fact that it can be done is enough motivation I think. This might display gaps in the API.

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bottine commented Mar 18, 2023

But that would be work for another PR in any case, no?

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Well, no, I want to see whether there are gaps in your API now.

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bottine commented Mar 18, 2023

I don't follow; what type of gaps would you like to see? Could you give me some signatures or more concrete infos?

@kim-em kim-em added the modifies-synchronized-file This PR touches a files that has already been ported to mathlib4, and may need a synchronization PR. label Mar 28, 2023
@eric-wieser eric-wieser added the not-too-late This PR was ready at the point mathlib3 was frozen: we will try to merge it and port it to mathlib4 label Jul 15, 2023
@@ -61,7 +61,7 @@ lemma ext {V : Type u} [quiver.{v₁} V] {W : Type u₂} [quiver.{v₂} W]
{F G : prefunctor V W}
(h_obj : ∀ X, F.obj X = G.obj X)
(h_map : ∀ (X Y : V) (f : X ⟶ Y),
F.map f = eq.rec_on (h_obj Y).symm (eq.rec_on (h_obj X).symm (G.map f))) : F = G :=
F.map f = eq.rec_on (h_obj X).symm (eq.rec_on (h_obj Y).symm (G.map f))) : F = G :=
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Why swap X and Y here?

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Can't say for sure, it's been a long time.

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Could you investigate and either revert or add a comment?

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@bottine bottine Jul 31, 2023

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I'm kind of out of the loop on all this, but after trying it out in gitpod, it seems swapping X and Y works for the ext lemma itself, but then of_bijective and further lemmas in the iso file get failing proofs, which I couldn't debug.
A comment as to that is what I should do?

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( ping @semorrison )

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kim-em commented Jul 30, 2023

bors d+

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bors bot commented Jul 30, 2023

✌️ bottine 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 The PR author may merge after reviewing final suggestions. and removed awaiting-review The author would like community review of the PR labels Jul 30, 2023
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