isosurface { //-------------------------------------------------------------

  function{ f_comma( x,y,z, 1) 
          }
  contained_by {sphere {0,1.5}}

  texture{
     pigment{ color rgb <0.7,1,0>} 
     finish { specular 0.1 roughness 0.1 phong 0.2 }
         }
  rotate<90,0,0>
  scale 1.2 
  translate< 0,1.5,0>
} // end of isosurface -------------------------------------------------------