function $(id) {
  return document.getElementById(id);
}

function showOldList() {
  $('link-list').style.display = 'none';
  $('old-link-list').style.display = 'block';
}

function showNowList() {
  $('link-list').style.display = 'block';
  $('old-link-list').style.display = 'none';
}