> x:=cos(t);

> y:=sin(t);

> z1:=-1:

> z2:=cos(3*t):

> z:=(1-s)*z1+s*z2;

> a:=plot3d([x,y,z],s=0..1,t=0..2*Pi,scaling=constrained,grid=[10,50]):

> x:=r*cos(t):

> y:=r*sin(t):

> z:=x^3-3*x*y^2:

> b:=plot3d([x,y,z],r=0..1,t=0..2*Pi,scaling=constrained,grid=[10,100],color=yellow):

> with(plots):

> c:=display(a,b):

> c;

> with(plottools):

> vrml(c,"c:/042/13/13-3.wrl",background_color=white);

maple