function show(layerName, tabName) 
{
	document.getElementById(layerName).style.display = '';
	
	if ( document.getElementById(tabName).className == 'tab last')
		document.getElementById(tabName).className= 'tab last active';
	else
		document.getElementById(tabName).className= 'tab active';
	 
}

function hide(layerName, tabName) 
{
	document.getElementById(layerName).style.display = 'none';
	 
	if ( document.getElementById(tabName).className == 'tab last active')
		document.getElementById(tabName).className= 'tab last';
	else
		document.getElementById(tabName).className= 'tab';
}

 
function show_next(layerName, tabName )
{
	hide(last_layer, last_tab );
    show(layerName, tabName);
    last_layer = layerName;
    last_tab = tabName;
}