static LS tok_combineRoundBrackets_keep(L<S> tok) {
  new L<S> l;
  for i over tok: {
    S t = tok.get(i);
    if (odd(i) && eq(t, "(")) {
      int j = findEndOfBracketPart(tok, i);
      l.add(joinSubList(tok, i, j));
      i = j-1;
    } else
      l.add(t);
  }
  ret l;
}