static LL<S> ai_spreadCertainIndicesC(L<S> tokPat, L<S> tokS, L<Int> indices) {
  int extra = l(tokS)-l(tokPat);
  if (extra < 0 || empty(indices)) ret emptyList();

  new LL<S> results;
  for (L<Int> spread : allSpreads(extra, l(indices))) {
    new L<S> tok;
    int pos = 0, iSpread = 0, iIndices = 0;
    for i over tokPat:
      if (!eq(get(indices, iIndices), i))
        tok.add(tokS.get(pos++));
      else {
        ++iIndices;
        int take = spread.get(iSpread++);
        tok.add(joinWithSpace(subList(tokS, pos, pos+take+1)));
        pos += take+1;
      }
    results.add(tok);
  }
  ret results;
}

Began life as a copy of #1017287