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

  function {
              y - (x*x + z*z)*0.5
	   }

  contained_by {box {<-1,-1,-1>, < 1, 1, 1>}}
  threshold 0
  accuracy 0.0001
  max_gradient 5

  texture { pigment{ color rgb<0.0,1,0.8>}
            finish { phong 1}
	  }
  scale 1.0
  rotate <-45, 25, 0>
  translate <-0, 1.4, 0>
} // end of isosurface -----------------------------------------------------