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[Merged by Bors] - refactor(geometry/manifold): use a sigma type for the total space of the tangent bundle #3966

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Redefine the total space of the tangent bundle to be a sigma type instead of a product type. Before

have p : tangent_bundle I M := sorry,
rcases p with ⟨x, v⟩,
-- x: M
-- v: E

After

have p : tangent_bundle I M := sorry,
rcases p with ⟨x, v⟩,
-- x: M
-- v: tangent_space I x

This seems more natural, and is probably needed to do Riemannian manifolds right. The drawback is that we can not abuse identifications any more between the tangent bundle to a vector space and a product space (but we can still identify the tangent space with the vector space itself, which is the most important thing).

@sgouezel sgouezel changed the title Sigma tangent refactor(geometry/manifold): replace the total space of the tangent bundle with a sigma type Aug 28, 2020
@sgouezel sgouezel changed the title refactor(geometry/manifold): replace the total space of the tangent bundle with a sigma type refactor(geometry/manifold): use a sigma type for the total space of the tangent bundle Aug 28, 2020
@bryangingechen bryangingechen added the awaiting-review The author would like community review of the PR label Aug 29, 2020
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Somehow this is causing a timeout in category_theory.adjunction.fully_faithful. @semorrison @sgouezel ?

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Fixed.

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This all seems reasonable to me. The proposed new definition seems more mathematically attractive, but I am not really equipped to judge whether it will make future constructions easier or harder.

src/geometry/manifold/basic_smooth_bundle.lean Outdated Show resolved Hide resolved
end
/-- The canonical identification between the tangent bundle to the model space and the product,
as a homeomorphim -/
def tangent_bundle_model_space_homeomorph : tangent_bundle I H ≃ₜ model_prod H E :=
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Presumably this could be a structomorphism? Would there be any benefit to registering that fact?

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@hrmacbeth thanks for taking a look!

As I understand it, this is blocking the update of the LFTCM tutorials, so there's slight urgency here. (Let's not let those bitrot again.) If @PatrickMassot wants us to wait for a review, or if @sgouezel wants to wait for Patrick, that's fine. Otherwise let's get this in.

bors d+

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bors bot commented Sep 3, 2020

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

@robertylewis robertylewis 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 Sep 3, 2020
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sgouezel commented Sep 4, 2020

Let's get this in, then. It can still be refactored/improved later if needed.

bors r+

@github-actions github-actions bot added the ready-to-merge All that is left is for bors to build and merge this PR. (Remember you need to say `bors r+`.) label Sep 4, 2020
bors bot pushed a commit that referenced this pull request Sep 4, 2020
…the tangent bundle (#3966)

Redefine the total space of the tangent bundle to be a sigma type instead of a product type. Before
```
have p : tangent_bundle I M := sorry,
rcases p with ⟨x, v⟩,
-- x: M
-- v: E
```
After
```
have p : tangent_bundle I M := sorry,
rcases p with ⟨x, v⟩,
-- x: M
-- v: tangent_space I x
```
This seems more natural, and is probably needed to do Riemannian manifolds right. The drawback is that we can not abuse identifications any more between the tangent bundle to a vector space and a product space (but we can still identify the tangent space with the vector space itself, which is the most important thing). 


Co-authored-by: Rob Lewis <Rob.y.lewis@gmail.com>
Co-authored-by: hrmacbeth <25316162+hrmacbeth@users.noreply.github.com>
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Canceled.

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@sgouezel I'm at least going to commit Heather's typo fix first!

bors r+

bors bot pushed a commit that referenced this pull request Sep 4, 2020
…the tangent bundle (#3966)

Redefine the total space of the tangent bundle to be a sigma type instead of a product type. Before
```
have p : tangent_bundle I M := sorry,
rcases p with ⟨x, v⟩,
-- x: M
-- v: E
```
After
```
have p : tangent_bundle I M := sorry,
rcases p with ⟨x, v⟩,
-- x: M
-- v: tangent_space I x
```
This seems more natural, and is probably needed to do Riemannian manifolds right. The drawback is that we can not abuse identifications any more between the tangent bundle to a vector space and a product space (but we can still identify the tangent space with the vector space itself, which is the most important thing). 


Co-authored-by: Rob Lewis <Rob.y.lewis@gmail.com>
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sgouezel commented Sep 4, 2020

Oops, sorry! (and thanks, of course)

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Pull request successfully merged into master.

Build succeeded:

@bors bors bot changed the title refactor(geometry/manifold): use a sigma type for the total space of the tangent bundle [Merged by Bors] - refactor(geometry/manifold): use a sigma type for the total space of the tangent bundle Sep 4, 2020
@bors bors bot closed this Sep 4, 2020
@bors bors bot deleted the sigma_tangent branch September 4, 2020 13:37
cipher1024 pushed a commit that referenced this pull request Sep 4, 2020
…the tangent bundle (#3966)

Redefine the total space of the tangent bundle to be a sigma type instead of a product type. Before
```
have p : tangent_bundle I M := sorry,
rcases p with ⟨x, v⟩,
-- x: M
-- v: E
```
After
```
have p : tangent_bundle I M := sorry,
rcases p with ⟨x, v⟩,
-- x: M
-- v: tangent_space I x
```
This seems more natural, and is probably needed to do Riemannian manifolds right. The drawback is that we can not abuse identifications any more between the tangent bundle to a vector space and a product space (but we can still identify the tangent space with the vector space itself, which is the most important thing). 


Co-authored-by: Rob Lewis <Rob.y.lewis@gmail.com>
PatrickMassot pushed a commit that referenced this pull request Sep 8, 2020
…the tangent bundle (#3966)

Redefine the total space of the tangent bundle to be a sigma type instead of a product type. Before
```
have p : tangent_bundle I M := sorry,
rcases p with ⟨x, v⟩,
-- x: M
-- v: E
```
After
```
have p : tangent_bundle I M := sorry,
rcases p with ⟨x, v⟩,
-- x: M
-- v: tangent_space I x
```
This seems more natural, and is probably needed to do Riemannian manifolds right. The drawback is that we can not abuse identifications any more between the tangent bundle to a vector space and a product space (but we can still identify the tangent space with the vector space itself, which is the most important thing). 


Co-authored-by: Rob Lewis <Rob.y.lewis@gmail.com>
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5 participants