var currentLayer = ""
function showLayer(layerName)
{
 if (currentLayer != "") hideLayer(currentLayer);
 eval("document" + layerRef + "['" + layerName + "']" + styleRef + ".visibility = 'visible'");
 currentLayer = layerName;
}
function hideLayer(layerName)
{
 eval("document" + layerRef + "['" + layerName + "']" + styleRef + ".visibility = 'hidden'");
 currentLayer = "";
}