> with(plots):with(plottools):

> 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]):

> a;

> vrml(a,"C:/My Documents/trfa/wrl/11-6.wrl",background_color=white);

>