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_next_li(li_tab_name) {
  var licurr = document.getElementById(li_tab_name);
  licurr.className='current_tab';
  document.getElementById(last_li_tab).className = '';
  last_li_tab=li_tab_name;
}