function openlisa(url){
   if(url == "" || url == "undefined") {
      url = "lisa-reisen.de/partner/student-online";
   }
   var lisawindow = window.open("http://" + url, "lisawindow", "width=750,height=612,toolbar=yes,location=yes,menubar=yes,resizable=yes,scrollbars=yes,status=no");
   lisawindow.focus();
}