#8800: Doctest coverage of categories - numerous coercion fixes
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Reporter: SimonKing | Owner:
Simon King
Type: defect | Status:
needs_work
Priority: major | Milestone:
sage-4.6.1
Component: categories | Keywords:
categories doctests
Author: Simon King | Upstream:
N/A
Reviewer: | Merged:
Work_issues: change 32-bit test; remove forgetful coercion |
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Comment(by SimonKing):
Replying to [comment:58 lftabera]:
> However, with the coercion of embedded and non embedded number fields,
now addition is not associative.
As you (? I guess `luisfe == lftabera`) pointed out at
[http://groups.google.com/group/sage-
algebra/browse_thread/thread/889464bee6a6a036 sage-algebra], the actual
problem is not the non-associativity of the addition (after all, we have
different algebraic structures involved, so, there is no reason to expect
that it can be globally extended to something that is associative).
You convinced me that the actual problem is the fact that the coercions in
your example do not form a commuting triangle: Coercion from `K3` to `K2`
followed by forgetful coercion from `K2` to `K1` is not the same as the
forgetful coercion from `K3` to `K1`.
Hence, I have to modify the `_coerce_map_from_` of number fields and
probably also the merge method of `AlgebraicExtensionFunctor`.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/8800#comment:61>
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