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[Merged by Bors] - feat(geometry/manifold/charted_space): open subset of a manifold is a manifold #3442

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An open subset of a charted space is naturally a charted space. If the charted space has structure groupoid G (with G closed under restriction), then the open subset does also.

Most of the work is in topology/local_homeomorph, where it is proved that a local homeomorphism whose source is univ is an open embedding, and conversely.


I wrote this as an exercise in the local_homeomorph lemmas. Feel free to close this PR if it doesn't fit well in the library (for example, if it should follow later from more general theory).

@hrmacbeth hrmacbeth added the awaiting-review The author would like community review of the PR label Jul 18, 2020
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This looks great, thanks! I just have a few minor comments left.

bors d+

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bors bot commented Jul 19, 2020

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

hrmacbeth and others added 2 commits July 19, 2020 15:45
Co-authored-by: sgouezel <sebastien.gouezel@univ-rennes1.fr>
@hrmacbeth hrmacbeth removed the awaiting-author A reviewer has asked the author a question or requested changes label Jul 19, 2020
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bors r+

bors bot pushed a commit that referenced this pull request Jul 19, 2020
… manifold (#3442)

An open subset of a charted space is naturally a charted space.  If the charted space has structure groupoid `G` (with `G` closed under restriction), then the open subset does also.

Most of the work is in `topology/local_homeomorph`, where it is proved that a local homeomorphism whose source is `univ` is an open embedding, and conversely.
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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 Jul 19, 2020
bors bot pushed a commit that referenced this pull request Jul 19, 2020
… manifold (#3442)

An open subset of a charted space is naturally a charted space.  If the charted space has structure groupoid `G` (with `G` closed under restriction), then the open subset does also.

Most of the work is in `topology/local_homeomorph`, where it is proved that a local homeomorphism whose source is `univ` is an open embedding, and conversely.
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bors bot commented Jul 19, 2020

Pull request successfully merged into master.

Build succeeded:

@bors bors bot changed the title feat(geometry/manifold/charted_space): open subset of a manifold is a manifold [Merged by Bors] - feat(geometry/manifold/charted_space): open subset of a manifold is a manifold Jul 19, 2020
@bors bors bot closed this Jul 19, 2020
@bors bors bot deleted the open-embedding-local-homeomorph branch July 19, 2020 22:26
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3 participants