remove_unselected = function() {
  $('subheading').innerHTML = 'Comparison';
  at_least_one_checked = false;
  $$('input.compare_checkbox').each (function(element) {
    if (element.checked) {
      at_least_one_checked = true;
    }
  })
  if (at_least_one_checked) {
    $$('input.compare_checkbox').each (function(element) {
      if (!element.checked) {
        element.parentNode.parentNode.remove();
      }
    })
  }
}