var current_showing = '';
	
	function show_submenu(which) {
	
		if (current_showing == '') {
			current_showing = which;
			document.getElementById(which).style.display = 'block'; 
		} else {
			if (current_showing != which) {
					document.getElementById(which).style.display = 'block'; 
					document.getElementById(current_showing).style.display = 'none'; 
					current_showing = which;
					
			}
		}
	}