static ItIt<IntRange> stepIntRange(final int length, final IntRange biggerRange, final int stepSize) {
  ret iteratorFromFunction(new F0<IntRange> {
    int i = biggerRange.start;
    
    public IntRange get() {
      if (i+length > biggerRange.end) null;
      IntRange r = intRange(i, i+length);
      i += stepSize;
      ret r;
    }
  });
}