static <A, B> O[] pairsToParams(Collection<Pair<A, B>> l) {
  O[] array = new O[l(l)*2];
  Iterator<Pair<A, B>> it = iterator(l);
  for (int i = 0; i < l(array); i += 2) {
    Pair p = it.next();
    array[i] = p.a;
    array[i+1] = p.b;
  }
  ret array;
}