static Map<S, L<Int>> lcRenumberTopLevelEncodings(LineCompCompressor lc, O... _) {
  ret lcRenumberTopLevelEncodings(lc.finalEncodings, _);
}

// out parameter: Map<Int> mapping (returns the forward mapping)
static Map<S, L<Int>> lcRenumberTopLevelEncodings(Map<S, L<Int>> encodings, O... _) {
  new LinkedHashMap<S, L<Int>> out;
  new Map<Int> map;
  setOutParameter(_, mapping := map);
  for (S file, L<Int> l : encodings) {
    new L<Int> l2;
    for (int i : l) {
      Int j = map.get(i);
      if (j == null)
        map.put(i, j = l(map)+1);
      l2.add(j);
    }
    out.put(file, l2);
  }
  ret out;
}

Began life as a copy of #1028765