Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

image of a subgroup #2201

Merged
merged 14 commits into from
Jan 22, 2025
Merged

image of a subgroup #2201

merged 14 commits into from
Jan 22, 2025

Conversation

Alizter
Copy link
Collaborator

@Alizter Alizter commented Jan 17, 2025

Here we introduce the image of a subgroup under a group homomorphism. This is obviously a generalisation of what exists in Image.v however since subgroup_group (maximal_subgroup G) isn't definitionally G, it makes working with the "standard image" a little bit more finicky, so I deemed it was not worth merging them.

I therefore opted to introduce this version specifically for subgroups and proved some standard properties about it.

We show that images are adjoint to preimages and images of normal subgroups under a surjective homomorphism are normal.

@Alizter Alizter requested a review from jdchristensen January 17, 2025 14:15
theories/Algebra/Groups/Subgroup.v Outdated Show resolved Hide resolved
theories/Algebra/Groups/Subgroup.v Outdated Show resolved Hide resolved
theories/Algebra/Groups/Subgroup.v Outdated Show resolved Hide resolved
@Alizter Alizter force-pushed the ps/rr/image_of_a_subgroup branch from 770d187 to fdcf4d3 Compare January 21, 2025 08:49
@Alizter
Copy link
Collaborator Author

Alizter commented Jan 21, 2025

I've also absorbed Kernel since it didn't make much sense for this to be a separate file. It is a special case of subgroup_preimage so I've redefined it as that with no issues.

@Alizter
Copy link
Collaborator Author

Alizter commented Jan 21, 2025

I also added some more comments and reorganised some things in Subgroup.v.

@Alizter Alizter requested a review from jdchristensen January 21, 2025 11:21
Copy link
Collaborator

@jdchristensen jdchristensen left a comment

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

I left one idea for an optional improvement, but feel free to insert a TODO instead.

theories/Algebra/Groups/Subgroup.v Outdated Show resolved Hide resolved
theories/Algebra/Groups/Subgroup.v Outdated Show resolved Hide resolved
@Alizter Alizter requested a review from jdchristensen January 21, 2025 22:16
Copy link
Collaborator

@jdchristensen jdchristensen left a comment

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Just one optional comment.

theories/Algebra/Groups/Subgroup.v Outdated Show resolved Hide resolved
@Alizter Alizter force-pushed the ps/rr/image_of_a_subgroup branch from 011d674 to 9f85dd5 Compare January 22, 2025 00:06
@Alizter
Copy link
Collaborator Author

Alizter commented Jan 22, 2025

I've just force pushed to resolve the conflicts. The latest commit was new which flipped the direction of the kernel equivalence and made the sigma types easier to see.

@Alizter Alizter merged commit 03ff069 into HoTT:master Jan 22, 2025
10 checks passed
@Alizter Alizter deleted the ps/rr/image_of_a_subgroup branch January 22, 2025 00:09
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
Labels
None yet
Projects
None yet
Development

Successfully merging this pull request may close these issues.

2 participants