12-3

> restart;

> a:=2:;

> r:=a+cos(u/2)*sin(v)-sin(u/2)*sin(2*v):;

> x:=r*cos(u):;

> y:=r*sin(u):;

> z:=sin(u/2)*sin(v)+cos(u/2)*sin(2*v):;

> p:=plot3d([x,y,z],v=0..2*Pi,u=-Pi/4..3*Pi/2,scaling=constrained):;

> p;

> with(plottools);

> vrml(p,"c:/program files/maple 6/beauty/12-3.wrl",background_color=white);

>