Subtraction Between two layers?

 Hi,

I just started cadence couple of days back for designing my patterns, I wanted to subtract two layers and already wrote a code but not sure its a right one or not. Could anyone help me please and let me know is this a right on or not,

 load("/usr/cdscad/libw/utils/rectw.il")


procedure( subtraction( @optional origin ww tlength outlayer)
(prog (xx yy np xo yo lw)

   subl1 = nil
   subl2 = nil

   xo = xCoord(origin)
   yo = yCoord(origin)
   


;; Draw First rect Layer

   xx = xo
   yy = yo-ww/2.0
   r = rectw(xx yy tlength ww "metal1")
 subl1 = append(subl1, list(r))

;; Draw Second rect Layer

   xx = xo
   yy = yo-ww/2.0
   r = rectw(xx yy tlength ww "metal2")
  subl2 = append(subl2, list(r))

dbLayerAndNot((getEditRep) outlayer subl1 subl2)

)

)

Thanks