anchor.diff:    }
   
     factory NumberEnumerable.fromRange(int start, int count) {
  -    return new _RangeIterable(start, count);
  +    return new _RangeEnumerable(start, count);
     }
  -
  -  int get length => count();
   
     num sum() {
       num theSum = 0;
  
positive.code:   const _SimpleNumEnumerable(this._source) : super();
  
    Iterator<T> iterator() => _source.iterator();
  }
  
  class _FuncNumEnumerable<TSource> extends NumberEnumerable {
  
negative.code:   const _FuncNumEnumerable(this._source, this._func) : super();
  
    Iterator<num> iterator() => _func(_source.iterator());
  
    int get length => count();
  }
  
  class _RangeEnumerable extends NumberEnumerable<int> {
    final int _start;
    final int _count;
  
    const _RangeEnumerable(this._start, this._count);
  
    Iterator<int> iterator() => new _RangeIterator(_start, _count);
  
    int get length => count();
  }
  
  class _RangeIterator implements Iterator<int> {
  