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:     return new _RangeList(_start + start * _step, _step, end - start);
    }
  
    @override
    String toString() {
      if (_length == 0) {
        return 'range()';
  