static L<S> dropPunctuationAtEnd_keep = litlist("*", "<", ">", "]", ")", "}");

static L<S> dropPunctuationAtEnd(L<S> tok) {
  tok = new ArrayList<S>(tok);
  for (int i = tok.size()-2; i > 0; i -= 2) {
    S t = tok.get(i);
    if (t.length() == 1 && !Character.isLetter(t.charAt(0)) && !Character.isDigit(t.charAt(0)) && !dropPunctuationAtEnd_keep.contains(t)) {
      tok.remove(i);
      tok.remove(i);
    } else break;
  }
  return tok;
}

static S dropPunctuationAtEnd(S s) {
  ret join(dropPunctuationAtEnd(nlTok(s)));
}