anchor.diff:      }
     }
   
  +  @override
     _RangeList sublist(int start, [int end]) {
       if (end == null) {
         end = length - 1;
  
positive.code: library range;
  
  import 'dart:collection';
  import 'src/utils.dart';
  
  /**
  
negative.code: 
    _RangeIterator(this._start, this._step, this._length);
  
    @override
    num get current => _current;
  
    @override
    bool moveNext() {
      if (_index == _length) {
        _current = null;
  