function read_cookie (key) {
   var cookie_string = "" + document.cookie;
   var cookie_array = cookie_string.split("; ");

   for (var i = 0; i < cookie_array.length; ++ i) {
      var single_cookie = cookie_array[i].split("=");
      if (single_cookie.length != 2)
         continue;
      var name  = unescape (single_cookie[0]);
      var value = unescape (single_cookie[1]);

      // Return cookie if found:
      if (key == name)
         return value;
   }
   return null;
}

function write_cookie (name, value, path) {
   var expiration_date = new Date();
   expiration_date.setYear(expiration_date.getYear()+20);
   expiration_date = expiration_date.toGMTString();

   var persistent_cookie_string = escape(name) + "=" + escape(value) + "; expires=" + expiration_date;
   if (path != null)
      persistent_cookie_string += "; path=" + path;
   document.cookie = persistent_cookie_string;
   if (read_cookie(name)!=value) {
      var session_cookie_string = escape(name) + "=" + escape(value);
      if (path != null)
         session_cookie_string += "; path=" + path;
      document.cookie = session_cookie_string;
   }
}

function showonce(element_id) {
   //alert("attach now");
   //debugger
   if (document.domain!="www.prognosis.nl" && document.domain!="www.prognosis.de")
      return;
   if (read_cookie(element_id)=="shown") {
      hide(element_id);
   } else {
      document.getElementById(element_id).style.visibility= "visible";
      setTimeout("hide('"+element_id+"')", 20000);
      write_cookie(element_id, "shown", "/");
   }
}

function hide(element_id) {
   document.getElementById(element_id).style.visibility= "hidden";
}