// clever index of tokenized strings
// maintaining one CI-sorted list per token position
sclass PositionalTokenIndex {
  L<LLS> sorts = new L; // token index -> entries sorted by token at index
  
  void addAll(LLS toks) {
    if (empty(toks)) ret;
    for (LS tok : toks)
      for (int i = 1; i < l(tok); i += 2) {
        LL<S> idx = listGetOrCreate ArrayList(sorts, i/2);
        idx.add(tok);
      }
    sort();
  }
  
  void sort {
    for i over sorts: {
      int j = i*2+1;
      sortInPlaceByCalculatedFieldIC(sorts.get(i),
        func(LS tok) -> S { tok.get(j) });
    }
  }
}