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[Merged by Bors] - feat(linear_algebra/exterior_algebra): Add an exterior algebra #4297

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@eric-wieser eric-wieser commented Sep 28, 2020

This adds the basic exterior algebra definitions using a very similar approach to universal_enveloping_algebra.
It's based off the exterior_algebra branch, dropping the wedge stuff for now as development in multilinear maps is happening elsewhere.

Co-authored-by: Adam Topaz github@adamtopaz.com
Co-authored-by: Zhangir Azerbayev zazerbayev@gmail.com


This will conflict with #4299, I don't really care which goes in first.

@eric-wieser eric-wieser added the awaiting-review The author would like community review of the PR label Sep 28, 2020
Comment on lines 19 to 20
It is endowed with the structure of an `R`-algebra. Some results only hold at the level of
generality of an `S`-module `M` and the space `exterior_algebra S N`.
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I don't understand the meaning of the last sentence.

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Removed, it was part of the other branch that I decided to leave out for now

The canonical quotient map `tensor_algebra R M → exterior_algebra R M`.
-/
protected def quot : tensor_algebra R M →ₐ[R] exterior_algebra R M :=
ring_quot.mk_alg_hom R _
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Here and below, don't indent the first line after :=. (Indenting happens before the := when the theorem statement runs over more than one line, but then the definition/proof starts again in the first column.)

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Removed this definition entirely, it wasn't used and I'm not yet convinced it was useful.

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Otherwise, looks great!

@semorrison semorrison 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 Sep 28, 2020
@eric-wieser eric-wieser 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 Sep 28, 2020
Co-authored-by: Adam Topaz <github@adamtopaz.com>
Co-authored-by: Zhangir Azerbayev <zazerbayev@gmail.com>
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eric-wieser commented Sep 28, 2020

Rebased on the merge of #4299 to eliminate some Ms

@Vierkantor Vierkantor self-requested a review September 30, 2020 08:55
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Thanks! I have a couple of remarks, but fairly minor.

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@Vierkantor Vierkantor 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 Sep 30, 2020
Co-authored-by: Vierkantor <Vierkantor@users.noreply.github.com>
@eric-wieser eric-wieser 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 Sep 30, 2020
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Thank you for the fixes! It looks ready to merge to me, if we add a variables statement like in daf239d.

bors d+

`cond : ∀ m : M, f m * f m = 0`, this is the canonical lift of `f` to a morphism of `R`-algebras
from `exterior_algebra R M` to `A`.
-/
def lift {A : Type*} [semiring A] [algebra R A] (f : M →ₗ[R] A) (cond : ∀ m, f m * f m = 0) :
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Thank you so much for the cleanup PR! I pushed a commit to a new branch, adding the variables statement. If you agree with it, could you add it to this branch?

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bors bot commented Oct 1, 2020

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

@Vierkantor Vierkantor 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 Oct 1, 2020
…rameters

Co-authored-by: Vierkantor <vierkantor@vierkantor.com>
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bors r+

bors bot pushed a commit that referenced this pull request Oct 1, 2020
This adds the basic exterior algebra definitions using a very similar approach to `universal_enveloping_algebra`.
It's based off the `exterior_algebra` branch, dropping the `wedge` stuff for now as development in multilinear maps is happening elsewhere.

Co-authored-by: Adam Topaz <github@adamtopaz.com>
Co-authored-by: Zhangir Azerbayev <zazerbayev@gmail.com>
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bors bot commented Oct 1, 2020

This PR was included in a batch that was canceled, it will be automatically retried

bors bot pushed a commit that referenced this pull request Oct 1, 2020
This adds the basic exterior algebra definitions using a very similar approach to `universal_enveloping_algebra`.
It's based off the `exterior_algebra` branch, dropping the `wedge` stuff for now as development in multilinear maps is happening elsewhere.

Co-authored-by: Adam Topaz <github@adamtopaz.com>
Co-authored-by: Zhangir Azerbayev <zazerbayev@gmail.com>
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bors bot commented Oct 1, 2020

Pull request successfully merged into master.

Build succeeded:

@bors bors bot changed the title feat(linear_algebra/exterior_algebra): Add an exterior algebra [Merged by Bors] - feat(linear_algebra/exterior_algebra): Add an exterior algebra Oct 1, 2020
@bors bors bot closed this Oct 1, 2020
@bors bors bot deleted the eric-wieser/exterior_algebra-def branch October 1, 2020 16:43
adomani pushed a commit that referenced this pull request Oct 7, 2020
This adds the basic exterior algebra definitions using a very similar approach to `universal_enveloping_algebra`.
It's based off the `exterior_algebra` branch, dropping the `wedge` stuff for now as development in multilinear maps is happening elsewhere.

Co-authored-by: Adam Topaz <github@adamtopaz.com>
Co-authored-by: Zhangir Azerbayev <zazerbayev@gmail.com>
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