> with(plots):with(plottools):

> x:=cos(t):y:=sin(t):

> z1:=-1.5:z2:=x:z:=(1-s)*z1+s*z2:

> a:=plot3d([x,y,z],s=0..1,t=Pi/2..3*Pi/2,scaling=constrained,grid=[5,50]):

> b:=reflect(a,[[0,0,0],[0,0,1],[0,-1,2]]):

> c:=display(a,b):

> d:=rotate(c,0,Pi/2,0):

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

> f:=rotate(c,0,3*Pi/2,0):

> h:=display(c,d,e,f):

> h;

> vrml(h,"C:/My Documents/trfa/wrl/11-3.wrl",background_color=white);

>