static ItIt<Int> countIterator_exclusive(int a default 0, int b) {
  ret new ItIt<Int>() {
    int i = a;
    
    public bool hasNext() { ret i < b; }
    public Int next() { ret i++; }
  };
}

static <A> ItIt<A> countIterator_exclusive(int a default 0, int b, IF1<Int, A> f) {
  ret mapI_if1(f, countIterator_exclusive(a, b));
}