Warning, the name changecoords has been redefined

> x0:=tan(t):

> y0:=sec(t):

> z0:=0:

> x:=cos(s)*x0-sin(s)*z0:

> y:=y0:

> z:=sin(s)*x0+cos(s)*z0:

> a:=plot3d([x,y,z],s=0..2*Pi,t=0..Pi/2-0.3,scaling=constrained):

> b:=plot3d([x,-y,z],s=0..2*Pi,t=0..Pi/2-0.3,scaling=constrained):

> c:=display(a,b):

> c;

> vrml(c,"c:/042/12/12-4.wrl",background_color=brown);

>