var i = 1;
var w = "layer";

var isDOM = document.getElementById?true:false;
var isNN = document.layers?true:false;
var isIE = document.all?true:false;

function verbergen(name) {
if (isDOM) document.getElementById(name).style.visibility="hidden";
if (isIE) document.all[name].style.visibility="hidden";
if (isNN) document.layers[name].visibility="hidden";
}

function zeigen(name) {
if (isDOM) document.getElementById(name).style.visibility="visible";
if (isIE) document.all[name].style.visibility="visible";
if (isNN) document.layers[name].visibility="visible";
}

function click(num){
verbergen(eval('"' + w + i +'"'));
zeigen(eval('"' + w + num +'"'));
i = num;
}