protected boolean isPlaceHolder( String to_check ){
          return ( to_check.equals("Add1") || to_check.equals("Add2") || 
                   to_check.equals("Mul1") || to_check.equals("Mul1") ||
                   to_check.equals("Div1") || to_check.equals("Div2") ||
                   to_check.equals("Load1")|| to_check.equals("Load2")||
                   to_check.equals("Int1") );
                 
     }