function random_div(/* ...*/) {

      var cnt = 0;
      var val;
      for (var i = 0; i < arguments.length; i++) {
         val = arguments[i];
         if (val > '') {
            cnt++;
            document.getElementById(val).style.display = "none";
         }
      }
      var div_idx = Math.round( cnt * Math.random() + 0.5) - 1;
      val = arguments[div_idx];
      document.getElementById(val).style.display = "block";
   }
   function rotate_div(/* ...*/) {

      var cnt = 0;
      var val;
      var last_val, style_val;
      for (var i = 0; i < arguments.length; i++) {
         val = arguments[i];
         if (val > '') {
            cnt++;
            style_val = document.getElementById(val).style.display;
            if (style_val == 'block') {
               document.getElementById(val).style.display = "none";
               last_val = style_val;
            }
            else {
               if (last_val == 'block') {
                  document.getElementById(val).style.display = "block";
                  last_val = style_val;
               }
            }
         }
      }
      if (last_val == 'block') {
         val = arguments[0];
         document.getElementById(val).style.display = "block";
      }
   }
   function div_dummy() {

      random_div('sm_one','sm_two','sm_three','sm_four','sm_five','sm_six','sm_seven');
   }