#11780: Creating a polynomial ring over a number field results in a non-unique
polynomial ring over the rationals
-------------------------+--------------------------------------------------
Reporter: SimonKing | Owner: robertwb
Type: defect | Status: needs_review
Priority: major | Milestone: sage-4.7.2
Component: coercion | Keywords: non-unique polynomial ring number
field
Work_issues: | Upstream: N/A
Reviewer: | Author: Simon King
Merged: | Dependencies:
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Changes (by newvalueoldvalue):
* status: new => needs_review
* author: => Simon King
Comment:
I did not run tests yet, and I am not able to provide a doc test that
shows that the bug is fixed. But it turns out that the patch that I just
attached solves the problem I met while working at #10667, and thus I
change it into "needs review".
The problem was as follows. Let `K.<i> = NumberField(x^2+1)`.
* During initialisation of `K['x','y','z']`, by one of the patches in my
patch chain, there is also an initialisation of a coercion from the base
ring.
* The construction of the coercion results in a call to
`_singular_ring_new`. It constructs a non-unique libsingular version of
`QQ[K.variable_name()]`.
* The construction of `QQ[K.variable_name()]` also involves the
registration of a coerce map from `QQ` to `QQ[K.variable_name()]`.
* Now, one constructs `K['x','y']`. Again, `_singular_ring_new` is
called. Again, it creates a ''__new__'' version of
`QQ[K.variable_name()]`, and again it tries to register the coercion. But
the coercion is already contained in the global coercion cache. Error.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/11780#comment:2>
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