> with(plots):
Warning, the name changecoords has been redefined

> EQ1:= z= x^3-y^3; EQ2:= z=x^3-3*x*y^2;

                                      3    3
                          EQ1 := z = x  - y


                                    3        2
                        EQ2 := z = x  - 3 x y

> display(implicitplot3d(EQ1,x=-10..10,y=-10..10,z=-100..100,numpoints=1
> 000,
>          style=patchcontour, axes=frame));
> 

> levelcurve:= level->
> implicitplot(subs(z=level,EQ1),x=-10..10,y=-10..10,legend=convert(leve
> l,string)):
> display(levelcurve(0), levelcurve(-10), levelcurve(-20),
> levelcurve(10), levelcurve(20));

> display(implicitplot3d(EQ2,x=-10..10,y=-10..10,z=-100..100,numpoints=1
> 000,
>          style=patchcontour, axes=frame));
> 

> levelcurve:= level->
> implicitplot(subs(z=level,EQ2),x=-5..5,y=-5..5,legend=convert(level,st
> ring)):
> display(levelcurve(0), levelcurve(-10), levelcurve(-20),
> levelcurve(10), levelcurve(20));#