feat(category_theory/noetherian): nonzero artinian objects have simple subobjects (#13972)
# Artinian and noetherian categories
An artinian category is a category in which objects do not
have infinite decreasing sequences of subobjects.
A noetherian category is a category in which objects do not
have infinite increasing sequences of subobjects.
We show that any nonzero artinian object has a simple subobject.
## Future work
The Jordan-Hölder theorem, following https://stacks.math.columbia.edu/tag/0FCK.
Co-authored-by: Scott Morrison <scott.morrison@gmail.com>