#9138: Categories for all rings
---------------------------------+------------------------------------------
   Reporter:  jbandlow           |          Owner:  nthiery                     
                  
       Type:  defect             |         Status:  needs_work                  
                  
   Priority:  major              |      Milestone:  sage-4.7.1                  
                  
  Component:  categories         |       Keywords:  introspection, categories 
for rings           
Work_issues:  Steenrod algebras  |       Upstream:  N/A                         
                  
   Reviewer:                     |         Author:  Simon King                  
                  
     Merged:                     |   Dependencies:  sage-4.7, #11268, #11139, 
#9976, #9944, #11269
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Comment(by SimonKing):

 I am now fighting against some doc test failures, that are apparently due
 to the fact that many tests in
 `sage.rings.polynomial.multi_polynomial_ring` do not use the cache of
 polynomial rings, in order to demonstrate features of ring classes that
 would otherwise hardly be used.

 Problem: If there is a ring in the cache, together with a coerce map from
 its base ring, then the coerce map is cached as well. Later, if one
 constructs an isomorphic ring that is ''not'' in the cache of rings, then
 the ring will evaluate equal to the previously constructed ring, and thus
 looking up the coerce map yields a map with the wrong codomain.

 Difficult.

-- 
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/9138#comment:75>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica, 
and MATLAB

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