static ItIt<Int> countIterator_exclusive(int a, int b) {
  ret new ItIt<Int>() {
    int i = a;
    
    public bool hasNext() { ret i < b; }
    public Int next() { ret i++; }
  };
}

static ItIt<Int> countIterator_exclusive(int b) {
  ret countIterator_exclusive(0, b);
}

static <A> ItIt<A> countIterator_exclusive(int a, int b, IF1<Int, A> f) {
  ret mapI(countIterator_exclusive(a, b), f);
}