I forwarded it to our team list.
I suppose, that your homomorphism uses Singulars map internally.
That should be a good solution for more than two parallel
substitutions.
Michael
On 3 Sep., 08:18, William Stein <wst...@gmail.com> wrote:
> Hi Martin (and Sage-devel),
>
> I discovered that polynomial substitution is badly inconsistent between the
> symbolic ring and multivariate polynomials:
>
> sage: R.<x,y> = QQ[]
> sage: f = x + 2*y
> sage: f.subs(x=y,y=x)
> 3*y
> sage: var('x,y')
> sage: f = x + 2*y
> sage: f.subs(x=y,y=x)
> 2*x + y
>
> Seehttp://trac.sagemath.org/sage_trac/ticket/6873for more and a proposal
> about how to solve this.
>
> William
>
> --
> William Stein
> Associate Professor of Mathematics
> University of Washingtonhttp://wstein.org
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