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

Elementary topos nonsense #411

Open
wants to merge 12 commits into
base: main
Choose a base branch
from
Open

Elementary topos nonsense #411

wants to merge 12 commits into from

Conversation

plt-amy
Copy link
Member

@plt-amy plt-amy commented Jul 19, 2024

watch this space but not too closely

@plt-amy
Copy link
Member Author

plt-amy commented Jul 19, 2024

oh, she's alive!

@TOTBWF
Copy link
Collaborator

TOTBWF commented Jan 10, 2025

What needs to be done to take this out of draft status? Working on injective objects right now, and I'd like to show that every subobject classifier is injective 🙂

@plt-amy
Copy link
Member Author

plt-amy commented Jan 10, 2025

I guess what's here is mostly done, there's just not a lot of it

@plt-amy plt-amy force-pushed the aliao/elementary-topoi branch 3 times, most recently from 9fdee2c to 106ce8c Compare March 7, 2025 14:01
@plt-amy plt-amy changed the base branch from main to aliao/no-biimp March 7, 2025 14:01
Base automatically changed from aliao/no-biimp to main March 7, 2025 17:38
@plt-amy plt-amy force-pushed the aliao/elementary-topoi branch from 23a1e6c to 1c9be5c Compare March 7, 2025 17:39
@plt-amy plt-amy marked this pull request as ready for review March 7, 2025 18:06
@plt-amy plt-amy changed the title wip: elementary topos nonsense Elementary topos nonsense Mar 7, 2025
@plt-amy plt-amy requested review from TOTBWF and ncfavier March 7, 2025 18:08
@plt-amy plt-amy force-pushed the aliao/elementary-topoi branch from 297f881 to 376903d Compare March 7, 2025 18:11
Copy link
Collaborator

@TOTBWF TOTBWF left a comment

Choose a reason for hiding this comment

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

Looks great, only have a couple of minor nits.

It would also be cool to prove that the displayed category of subobjects has a skeletal generic object iff it has a subobject classifier, but that could be done in a separate PR.

$\name{A} : A \to \Omega$ into the presheaf of sieves on $\cC$ is valued
in closed sieves.

First, suppose that the domain of $A' \mono A$ is indeed a sheaf. First,
Copy link
Collaborator

Choose a reason for hiding this comment

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

Two "First,"s in a row.

Copy link
Member Author

Choose a reason for hiding this comment

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

why after you're done assuming the other thing is the new first thing to do!

We can then compute, in $\psh(\cC)$, the name of $A'$, resulting in a
natural transformation $\name{A'} : A \to \Omega$. It remains to show
that this transformation is actually valued in $\Omega_J$, i.e. that
each of the resulting sieves is closed. To this end, susppose we have
Copy link
Collaborator

Choose a reason for hiding this comment

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

Suggested change
each of the resulting sieves is closed. To this end, susppose we have
each of the resulting sieves is closed. To this end, suppose we have

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.

3 participants