> restart:

> 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=[5,50]):

> with(plots):

> with(plottools):

> vrml(a,"c:/My documents/87124/11/11-06.wrl",background_color=white):

> display(a);

>