#10963: More functorial constructions
-------------------------------------+-------------------------------------
       Reporter:  nthiery            |        Owner:  stumpc5
           Type:  enhancement        |       Status:  needs_review
       Priority:  major              |    Milestone:  sage-6.1
      Component:  categories         |   Resolution:
       Keywords:  days54             |    Merged in:
        Authors:  Nicolas M. Thiéry  |    Reviewers:  Simon King, Frédéric
Report Upstream:  N/A                |  Chapoton
         Branch:                     |  Work issues:
  public/ticket/10963                |       Commit:
   Dependencies:  #11224, #8327,     |  eb7b486c6fecac296052f980788e15e2ad1b59e4
  #10193, #12895, #14516, #14722,    |     Stopgaps:
  #13589, #14471, #15069, #15094,    |
  #11688, #13394, #15150, #15506     |
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Comment (by SimonKing):

 PS:

 Replying to [comment:409 vbraun]:
 > There is also a consistency issue about user-supplied axioms: They must
 not induce further relations for the categories and axioms that Sage ships
 with.

 Why?

 Imagine Wedderburn lived today. We wouldn't know that all finite division
 rings are commutative. Hence, `Rings.Division().Finite()` and
 `Fields().Finite()` would be distinct categories. Then, Wedderburn proves
 his theorem. We add his theorem as a relation, and as a result we have a
 new relation between previously distinct categories in Sage. I don't think
 this would be a problem.

 The only requirement: When adding a new axiom or a new basic category, the
 original commutative monoid must be extended, and the ordering of the
 enlarged monoid must be compatible with the ordering of the original
 monoid; The original monoid must be an ordered submonoid of the enlarged
 monoid. By this requirement, we can keep using the Gröbner basis we had
 for the relations in the original monoid.

--
Ticket URL: <http://trac.sagemath.org/ticket/10963#comment:411>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica, 
and MATLAB

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