sS simpleWikipedia_cached(S topic) {
  File f = newFile(simpleWikipedia_cacheDir(), uniqueFileNameUsingMD5_80(topic));
  if (fileExists(f)) ret loadTextFile(f);
  S page = simpleWikipedia(topic);
  saveTextFile(f, page);
  setFileMetaField(f, "Topic", topic);
  ret page;
}