#10963: More functorial constructions
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       Reporter:  nthiery                                                |      
   Owner:  stumpc5                                                              
                        
           Type:  enhancement                                            |      
  Status:  needs_work                                                           
                        
       Priority:  major                                                  |     
Milestone:                                                                      
                         
      Component:  categories                                             |    
Resolution:                                                                     
                          
       Keywords:                                                         |   
Work issues:  Reduce startup time by 5%. Avoid "recursion depth exceeded 
(ignored)". Trivial doctest fixes.
Report Upstream:  N/A                                                    |     
Reviewers:  Simon King                                                          
                         
        Authors:  Nicolas M. ThiƩry                                      |     
Merged in:                                                                      
                         
   Dependencies:  #11224, #8327, #10193, #12895, #14516, #14722, #13589  |      
Stopgaps:                                                                       
                        
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Comment (by SimonKing):

 Replying to [comment:53 nthiery]:
 >
 > But this would mean constructing a trivial category for finite
 commutative rings (there is currently no category code for finite
 commutative rings).

 That's the point: In my approach, this category would be constructed on
 the fly, by means of a dynamic construction.

 > Besides: should this be finite commutative rings? Or finite domains? Or
 finite euclidean rings? ...

 To be discussed. In the end of the day, this is a matter of what axioms we
 have for fields that do not hold for all division rings, and which are
 thus implied by adding `Finite()` to `Rings().Division()`.

 However, I do think that the category of finite commutative rings should
 be a super-category of the category of finite fields. But (with your
 patch):
 {{{
 sage: Rings().Finite() in Fields().Finite().all_super_categories()
 False
 }}}
 even though
 {{{
 sage: (Fields().Finite()).is_subcategory(Rings().Finite())
 True
 }}}

-- 
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/10963#comment:54>
Sage <http://www.sagemath.org>
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