function mostra_tendina(id)
	{
		 var list = document.getElementById("barra_menu_volatile");
  		 var items = list.getElementsByTagName("div");
	
    	for (var i = 0; i < items.length; i++) 
		{
			var id_temp = items[i].id;
			var class_temp = items[i].className;
				if (class_temp=="barra_menu_tendina")
				{
				document.getElementById(id_temp).style.visibility="hidden";
				document.getElementById(id_temp).style.display="none";
				}
		}
		
		if (id!="null")
		{
		document.getElementById(id).style.visibility="visible";
		document.getElementById(id).style.display="block";
		}
	}