static ItIt<ParsedWithTokens<S>> pwt_precedingTokens(int minTokens, int maxTokens, ListAndIndex<S> tok) {
  int remaining = countPrecedingTokens(tok);
  int iStart = tok.idx;
  ret countIterator_inclusive(
    min(minTokens, remaining),
    min(maxTokens, remaining),
    n -> pwt_raw(tok.list, iStart-n*2, iStart-1));
}