Hi, Dima; thanks for taking the time to help out a noob -- again.
This is what I did:

sage: a,b,y,z=var('a,b,y,z')
sage: p=z*x^2+x^2-(x^2+y^2)*(a*x-2*b*y)+z*y^2+y^2
sage: type(p)
<type 'sage.symbolic.expression.Expression'>

The book says that I should be able to do this:

sage: p.collect(x).collect(y)

And get this in return:

sage: 2*b*y*x^2 + 2*b*y^3−(a*x−z−1)*x^2−(a*x−z−1)*y^2

But instead, I get:

-a*x^3 + 2*b*x^2*y + 2*b*y^3 - (a*x - z - 1)*y^2 + x^2*z + x^2

???

On Sun, Aug 19, 2018 at 10:46 AM, Dima Pasechnik <dimp...@gmail.com> wrote:

> how is p created? what is the output of
>
>   type(p)
>
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