#19956: elements of finite field algebraic closure are not hashable
--------------------------------+------------------------
       Reporter:  vdelecroix    |        Owner:
           Type:  defect        |       Status:  new
       Priority:  major         |    Milestone:  sage-7.1
      Component:  finite rings  |   Resolution:
       Keywords:                |    Merged in:
        Authors:                |    Reviewers:
Report Upstream:  N/A           |  Work issues:
         Branch:                |       Commit:
   Dependencies:                |     Stopgaps:
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Changes (by vdelecroix):

 * cc: pbruin (added)


Old description:

> We have
> {{{
> sage: K = GF(2).algebraic_closure()
> sage: a = K.an_element()
> sage: hash(a)
> Traceback (most recent call last):
> ...
> TypeError: ...
> }}}
> and this prevent resultant computation of bivariate polynomials
> {{{
> sage: R.<x,y> = K[]
> sage: x.resultant(y)
> Traceback (most recent call last):
> ...
> TypeError: ...
> }}}

New description:

 We have
 {{{
 sage: K = GF(2).algebraic_closure()
 sage: a = K.an_element()
 sage: hash(a)
 Traceback (most recent call last):
 ...
 TypeError: ...
 }}}
 and this prevent resultant computation of bivariate polynomials
 {{{
 sage: R.<x,y> = K[]
 sage: x.resultant(y)
 Traceback (most recent call last):
 ...
 TypeError: ...
 }}}

 ------

 Just as a remark, the hash we had in sage-6.8 was '''completely''' broken
 {{{
 sage: F = GF(2).algebraic_closure()
 sage: z3 = F.gen(3)
 sage: z2 = F.gen(2)
 sage: hash(z2)
 15616093818140894
 sage: hash(z3+z2-z3)
 5386247743066594243
 }}}
 But thanks to #19016 the error now shows up!

--

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Ticket URL: <http://trac.sagemath.org/ticket/19956#comment:1>
Sage <http://www.sagemath.org>
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