static LS simpleWikipedia_allCachedTopics() {
  new LS topics;
  for (File f : listFilesWithExtension(simpleWikipedia_cacheDir(), ".infos")) {
    File f2 = fileInSameDir(f, dropSuffixIC(".infos", f.getName()));
    addIfNotNull(topics, getFileInfoField(f2, "Topic"));
  }
  ret topics;
}