var BuchungsFenster = null;
    function go() {
      if ( BuchungsFenster == null ) {
        BuchungsFenster = window.open("", "Buchungsanfrage", "toolbar=no, width=750, height=550, directories=no, status=yes, scrollbars=yes, resize=yes, menubar=no");
      } else {
         if ( BuchungsFenster.closed ) {
            BuchungsFenster = window.open("", "Buchungsanfrage", "toolbar=no, width=750, height=550, directories=no, status=yes, scrollbars=yes, resize=yes, menubar=no");
         } else {
            BuchungsFenster.focus();
         }
      }

      document.bkrequest.target="Buchungsanfrage";
      document.bkrequest.action="http://www.hoteldaten.com/koop-apis/wdba/dorequest.php";
      document.bkrequest.submit();
      document.bkrequest.action="go()";
      document.bkrequest.target="_self";
    }