static <A> Pair<A, Double> searchForMostSimilarByteArrayInMultiMap(MultiMap<A, byte[]> mm, byte[] a) {
  new Lowest<A> lowest;
  for (A key : keys(mm))
    for (byte[] b : mm.get(key))
      lowest.put(key, byteArraysTotalDiff(a, b));
  ret lowest.pair();
}