oldLayer=null;
function showLayer(layerName)
{
	if (oldLayer)
	{
		document.getElementById(oldLayer).style.visibility = 'hidden';
	}
	document.getElementById(layerName).style.visibility = 'visible';
	oldLayer=layerName;
}
function hideLayer(layerName)
{
	document.getElementById(layerName).style.visibility = 'hidden';
}