function show_foto() {
 	if(document.getElementById)
    document.getElementById("hintergrund").style.visibility = "visible";
	document.getElementById("vordergrund").style.visibility = "visible";
	}
	function hide_foto() {
 	if(document.getElementById)
    document.getElementById("hintergrund").style.visibility = "hidden";
	document.getElementById("vordergrund").style.visibility = "hidden";
	}
	
	function show_cad() {
 	if(document.getElementById)
    document.getElementById("hintergrund_cad").style.visibility = "visible";
	document.getElementById("vordergrund_cad").style.visibility = "visible";
	}
	function hide_cad() {
 	if(document.getElementById)
    document.getElementById("hintergrund_cad").style.visibility = "hidden";
	document.getElementById("vordergrund_cad").style.visibility = "hidden";
	}