function hideLayers()
{
  var navi = document.getElementById('navi');
  var lists = navi.getElementsByTagName('ul');
  var links;
  for(var i=0; i < lists.length; i++)
  {
    links = lists[i].getElementsByTagName('li');
    for(var j=1; j < links.length; j++)
    {
      links[j].className = "hidden";
    }
  }
}

function showLayers(layer)
{
  hideLayers();
  var list = document.getElementById(layer);
  var links = list.getElementsByTagName('li');
  for(var i = 1; i < links.length; i++)
  {
    links[i].className = "visible";
  }
}