anchor.diff:    EnumSet<E> removeAll(EnumSet<E> set) {
       int removed = _value & set.value;
       _value &= ~set.value;
  -    return new EnumSet<E>.fromValue(removed);
  +    return EnumSet<E>.fromValue(removed);
     }
   
     @override
  
positive.code:   _EnumSetIterable(this._enumSet, this._values);
  
    @override
    Iterator<E> get iterator => new _EnumSetIterator(_enumSet.value, _values);
  }
  
  class _EnumSetIterator<E> implements Iterator<E> {
    int _value;
    int _index;
    int _mask;
    final List<E> _values;
    E _current;
  
    _EnumSetIterator(this._value, this._values);
  
    @override
    E get current => _current;
  
    @override
    bool moveNext() {
      if (_value == 0) {
        return false;
      } else {
        if (_mask == null) {
          _index = _value.bitLength - 1;
          _mask = 1 << _index;
        }
        _current = null;
        while (_index >= 0) {
          if (_mask & _value != 0) {
            _current = _values[_index];
          }
          _mask >>= 1;
          _index--;
          if (_current != null) {
            break;
          }
        }
        return _current != null;
      }
    }
  }
  
negative.code:   bool get isNotEmpty => value != 0;
  
    /// Returns a new mutable enum set that contains the values of this set.
    EnumSet<E> clone() => EnumSet<E>.fromValue(value);
  
    @override
    int get hashCode => value.hashCode * 19;
  