static ItIt<Double> geometricIterator(double a, double b, double factor) {
  assertTrue("factor > 1", factor > 0);
  
  ret new ItIT<Double>() {
    double i = a;
    
    public bool hasNext() { ret i < b; }
    public Double next() { var j = i; i *= step; ret j; }
  };
}

static <A> ItIt<A> countIterator_exclusive_step(double a, double b, double step, IF1<Double, A> f) {
  ret mapI_if1(f, countIterator_exclusive_step(a, b, step));
}