Dear William, Dear Waldek, many thanks for your help!
I guess, the real problem is that (71) -> ex := ((-2*t*x*y)+(-2*t*x^2))/(y*(t^2*y^4+((-4*t^2)+(-2*t))*x*y^3+((-6*t^2)+1)*x^2*y^2+((-4*t^2)+(-2*t))*x^3*y+t^2*x^4)^(1/2)+t*y^3+(-x*y^2)+t*x^2*y) 2 - 2t x y - 2t x (71) -------------------------------------------------------------------------------------------- +------------------------------------------------------------------+ | 2 4 2 3 2 2 2 2 3 2 4 3 2 2 y\|t y + (- 4t - 2t)x y + (- 6t + 1)x y + (- 4t - 2t)x y + t x + t y - x y + t x y Type: Expression Integer (72) -> series(ex, t=0) 2 3 2 2 3 - 2x y - 2x - 2y - 2x y - 2x y - 2x 2 3 (72) --------------- t + -------------------------- t + O(t ) +----+ +----+ | 2 2 2 2 | 2 2 3 y\|x y - x y y \|x y - x y Type: UnivariatePuiseuxSeries(Expression Integer,t,0) is not correct in general, eg., when x*y > 0. In my case, I consider x and y in fact as formal power series in t themselves, and I think I also want that sqrt(x^2)=x. Martin _______________________________________________ Axiom-developer mailing list Axiom-developer@nongnu.org http://lists.nongnu.org/mailman/listinfo/axiom-developer