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

  function{  sqrt(x*x + z*z) 
             - abs(y) 
          }
  threshold 0
  accuracy 0.0001
  max_gradient 5
  contained_by {box {<-1,-1,-1>, < 1, 1, 1>}}
  //open
  texture { pigment{ color rgb<0.0,1,0.6>}
            finish { phong 1}
	  }
  scale 1.0
  rotate < 15, 25, 0>
  translate <-0, 1.0, 0>
} // end of isosurface -----------------------------------------------------