static IterableIterator<Int> countIterator_exclusive_step(final int a, final int b, final int step) {
  assertTrue("step > 0", step > 0);
  
  ret new IterableIterator<Int>() {
    int i = a;
    
    public bool hasNext() { ret i < b; }
    public Int next() { var j = i; i += step; ret j; }
  };
}

static ItIt<Double> countIterator_exclusive_step(double a, double b, double step) {
  assertTrue("step > 0", step > 0);
  
  ret new IterableIterator<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));
}

Began life as a copy of #1018109