> #sfb 6 feb 03
> with(plots);
> f:=x^2+y^2;
> E:=plot3d(f,x=-3..3,y=-3..3,title="cross sections",style=wireframe,shading=z,axes=boxed):
> curve:=[x,y,f];
> A:=spacecurve(eval(curve,x=1),y=-3..3,color=red,thickness=3):
> B:=spacecurve(eval(curve,y=2),x=-3..3,color=green,thickness=3):
> C:=spacecurve(eval(curve,y=1+x),x=-3..2,color=blue,thickness=3):
> 
> display(A,B,C,E,title="cross sections");
>