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

> c:=plot3d([x,y,x*y/(x^2+y^2)],r=0..1,t=0..2*Pi,scaling=constrained,grid=[20,50]):

> c;

> with(plottools):

> vrml(c,"c:/040/12/12-11.wrl",background_color=white):

>