static Map<S, Pair<Int>> indexTwoDArrayIC(LL<S> table) {
  if (table == null) null;
  Map<S, Pair<Int>> map = ciMap();
  for i over table: {
    LS row = table.get(i);
    for j over row:
      map.put(row.get(j), pair(i, j));
  }
  ret map;
}