> restart;

> with(plots):with(plottools):

Warning, the name changecoords has been redefined

> z:=z1:x:=cos(s)*x1-sin(s)*y1:y:=sin(s)*x1+cos(s)*y1:

> u:=arctan(cos(t)):

> a:=plot3d([x,y,z],s=0..Pi/2-2*u,t=-Pi/2..Pi/2,scaling=constrained):

> b:=rotate(a,0,0,Pi/2):

> c:=display(a,b):

> d:=rotate(c,0,0,Pi):

> e:=display(c,d):

> e;

> vrml(e,"c:/040/12/12-5.wrl",background_color=white):

>