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