document.observe('dom:loaded', function() {
  var currently_checked;
  var left_column  = $('column1');
  var right_column = $('column2');
     
    if (!left_column || left_column.hasClassName('expanded'))
        return;
    
  var elements  = left_column.select('li');
  var active_li = elements.first();
  if (active_li.hasClassName('active'))
    activate_li(active_li);
      
  function activate_li(list_item) {
    list_item.addClassName('active');
    currently_checked = list_item;
    right_column.className = "active_" + list_item.identify();
  }

  elements.invoke('observe', 'click', function(event) {
    if (currently_checked)
      currently_checked.removeClassName('active');

    activate_li(event.findElement('li'));
    event.stop();
  }.bindAsEventListener(this));
});