var pop = null;

function popdown() {
	if (pop) if (!pop.closed) pop.close();
}

function fenster(obj) {
	var url = obj;
	if (!url) return true;
	popdown();
	pop = window.open(url,'','width=300,height=550,left=100,top=100,screenX=10,screenY=10,menubar=no,statusbar=no,toolbar=no,scrollbars=yes,resizable=yes,hotkeys=no,location=no,status=no');
	return (pop) ? false : true;
}

window.onunload = popdown;
window.onfocus = popdown;