function openPopup(url) {
	fenster = window.open(url, "popup",
			"width=600,height=400,status=yes,scrollbars=yes,resizable=yes");
	fenster.focus();
}

var vis = 1;
function cover() {
	var cover = document.getElementById('cover');
	if (vis) {
		vis = 0;
		cover.style.display = 'block';
	} else {
		vis = 1;
		cover.style.display = 'none';
	}
}