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

  function { sin( 4 *y*2*pi ) /15
             + sqrt(x*x*4 + z*z*4) - 0.5 }
  threshold 0
  contained_by {box {<-1,0,-1>, < 1, 1, 1>}}
  max_gradient 10
  accuracy 0.005
  open  // optional

  texture {
            pigment{ color rgb<1,1,1>}
            finish { phong 0.51 reflection 0.2}
	  }
  scale 1
  rotate <0, 0, 0>
  translate < 0, 0, 0>
} // end of isosurface -----------------------------------------------------