#16340: Infrastructure for modelling full subcategories
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Reporter: nthiery | Owner:
Type: enhancement | Status: needs_review
Priority: major | Milestone: sage-6.4
Component: categories | Resolution:
Keywords: full | Merged in:
subcategories, homset | Reviewers: Darij Grinberg,
Authors: Nicolas M. Thiéry | Travis Scrimshaw
Report Upstream: N/A | Work issues:
Branch: | Commit:
public/categories/full_subcategories-16340|
d4c7a88563a397291b6cd5ddadb8f574cc1eedb5
Dependencies: | Stopgaps:
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Comment (by tscrim):
Replying to [comment:33 nthiery]:
> Thanks. I double checked on this, and mostly agree up to one point: I
> think Coxeter Groups should be a structure category, the extra
> structure being the chosen set of simple generators.
I don't think so. If we wanted the generators to be part of the structure
(definition), that should be the category of Coxeter syetems as it is much
more rigid than just the groups.
> > This made me wonder if we actually want the default category be a
> > structure category.
>
> I believe this would be dangerous. Being accidentally a structure
> category means that your homsets will miss some code that could be
> available. So just a missing feature. Whereas being accidentally a non
> structure category can let your homset inherit from code that is not
> applicable which can lead to wrong code.
I agree with this, although my thought is more about how many categories
will we have are structure categories. As I stated, we need more data and
I agree that having this default is the safe route.
> Besides, all the categories your changed should actually become
> CategoryWithAxioms at some point, which will have precisely the
> desired effect.
Probably.
> So now one could wonder whether having a CategoryWithAxiom be a non
> structure category is not a dangerous default. I believe it's ok,
> because for a category with axiom A.B, one only has to be careful
> about being a full subcategory or not if A is the category defining
> the axiom B. There are not soo many of them.
Most axioms that come to my mind adds extra structure, but we can see what
happens as we add more axioms.
> > I'm going to double-check to make sure I didn't miss any others and
> > I'd appreciate if someone else could do the same.
>
> Thanks!
Thanks for double-checking my double-check.
Replying to [comment:34 nthiery]:
> Possibly so. What would be the names for all the related methods (like
all_structure_categories)?
With this, we could keep the same names (although I believe the method
your referring to is `all_structure_super_categories`).
Are we all in agreement that we should change `is_structure_category` to
`has_additional_structure` and the current framework is a good enough to
merge in (since it could be extended at a later date to carry additional
info)?
--
Ticket URL: <http://trac.sagemath.org/ticket/16340#comment:35>
Sage <http://www.sagemath.org>
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