last_tab = 'tab1';

	function show(layerName) {
	document.getElementById(layerName).style.display = '';
	}

	function hide(layerName) {
	document.getElementById(layerName).style.display = 'none';
	}

	function show_next(tab_name) {
	document.getElementById(last_tab).className = 'tab';
	var curr = document.getElementById(tab_name);
	curr.className='tab_hover';
	hide(last_tab+'_data');
	show(tab_name+'_data');
	last_tab=tab_name;
	}
	
	function show_tab(tab_name) {
	document.getElementById(last_tab).className = 'tab';
	var curr = document.getElementById(tab_name);
	curr.className='tab_hover';
	hide(last_tab+'_data');
	show(tab_name+'_data');
	last_tab=tab_name;
	}