[GiNaC-list] arithmetic error on concat two expressions

[Stephen Montgomery-Smith]

Kraus Philipp wrote:
> Thanks, I see it, but if I create a derivatrion "diff" the sign is
> important:
> If I run formula.diff(a, 1):
>
> [0.5*(t-ax^3)^2]' => -(t-a*x^3)*x^3
> [0.5*(ax^3-t)^2]' => (a*x^3-t)*x^3
>

Those two formulae are mathematically equivalent.  -(u-v)=(v-u).