static Pair<L<File>> wordPairAudioRecordings(S word1, S word2) {
  ret wordPairAudioRecordings(pair(word1, word2));
}

static Pair<L<File>> wordPairAudioRecordings(Pair<S> pair) {
  new L<File> l1;
  new L<File> l2;
  for (File f : allRecordingsWithMarkers()) {
    S word = wordFromAudioFileName(f);
    if (eqic(word, pair.a))
      l1.add(f);
    else if (eqic(word, pair.b))
      l2.add(f);
  }
  ret pair(l1, l2);
}