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[Merged by Bors] - feat(representation_theory/group_cohomology_resolution): show k[G^(n + 1)] is free over k[G] #15501

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@101damnations 101damnations commented Jul 18, 2022

Defines an isomorphism $k[G^{n + 1}] \cong k[G] \otimes_k k[G^n].$ Also shows that given a $k$-algebra $R$ and a $k$-basis for a module $M,$ we get an $R$-basis of $R \otimes_k M.$ Then, using that, we show $k[G^{n + 1}]$ is free.


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@101damnations 101damnations changed the title feat(representation_theory/group_cohomology_resolution): show $k[G^{n + 1}]$ is free over $k[G]$ feat(representation_theory/group_cohomology_resolution): show k[G^{n + 1}] is free over k[G] Jul 18, 2022
@101damnations 101damnations changed the title feat(representation_theory/group_cohomology_resolution): show k[G^{n + 1}] is free over k[G] feat(representation_theory/group_cohomology_resolution): show k[G^(n + 1)] is free over k[G] Jul 18, 2022
@robertylewis robertylewis added the awaiting-review The author would like community review of the PR label Jul 19, 2022
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I've not looked at the later parts of this PR but here are some comments on the earlier parts.

src/algebra/big_operators/fin.lean Outdated Show resolved Hide resolved
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This is looking really nice now. I've read through to the end. Well done for making the proofs so compact!

src/ring_theory/tensor_product.lean Outdated Show resolved Hide resolved
src/logic/equiv/basic.lean Outdated Show resolved Hide resolved
@[simp] lemma prod_unique_apply {α β : Type*} [unique β] (x : α × β) :
prod_unique α β x = x.1 := rfl

@[simp] lemma prod_unique_symm_apply {α β : Type*} [unique β] (x : α) :
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Similarly here:

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@[simp] lemma prod_unique_symm_apply {α β : Type*} [unique β] (x : α) :
@[simp] lemma coe_prod_unique_symm {α β : Type*} [unique β] :
⇑(prod_unique α β).symm = pi.prod (id : α → α) default := rfl
lemma prod_unique_symm_apply {α β : Type*} [unique β] (x : α) :

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@101damnations 101damnations Aug 3, 2022

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It seems logic/equiv/basic doesn't import data/pi/algebra where pi.prod is defined, and vice versa :(

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Is there some kind of tool which finds the first file which imports both logic/equiv/basic and data/pi/algebra?

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@ocfnash ocfnash added awaiting-author A reviewer has asked the author a question or requested changes and removed awaiting-review The author would like community review of the PR labels Aug 2, 2022
@101damnations 101damnations added awaiting-review The author would like community review of the PR and removed awaiting-author A reviewer has asked the author a question or requested changes labels Aug 3, 2022
@eric-wieser eric-wieser self-requested a review August 8, 2022 23:20
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Thanks 🎉

bors merge

@leanprover-community-bot-assistant leanprover-community-bot-assistant 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 Aug 11, 2022
bors bot pushed a commit that referenced this pull request Aug 11, 2022
…+ 1)] is free over k[G] (#15501)

Defines an isomorphism $k[G^{n + 1}] \cong k[G] \otimes_k k[G^n].$ Also shows that given a $k$-algebra $R$ and a $k$-basis for a module $M,$ we get an $R$-basis of $R \otimes_k M.$ Then, using that, we show $k[G^{n + 1}]$ is free.
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bors bot commented Aug 11, 2022

Pull request successfully merged into master.

Build succeeded:

@bors bors bot changed the title feat(representation_theory/group_cohomology_resolution): show k[G^(n + 1)] is free over k[G] [Merged by Bors] - feat(representation_theory/group_cohomology_resolution): show k[G^(n + 1)] is free over k[G] Aug 11, 2022
@bors bors bot closed this Aug 11, 2022
@bors bors bot deleted the monoid-algebra-basis2 branch August 11, 2022 21:14
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6 participants