static <A, B> LPair<A, B> zipTwoListsToPairs_longer(L<A> l1, L<B> l2) {
  int n = max(l(l1), l(l2));
  LPair<A, B> out = emptyList(n);
  for i to n: addPair(out, _get(l1, i), _get(l2, i));
  ret out;
}