anchor.diff:  
     /// Create a set containing the [values]. If [fixed] is `true` the set is
     /// immutable.
  -  factory EnumSet.fromValues(Iterable<E> values, {bool fixed: false}) {
  +  factory EnumSet.fromValues(Iterable<E> values, {bool fixed = false}) {
       if (fixed) {
  -      return new _ConstEnumSet<E>.fromValues(values);
  +      return _ConstEnumSet<E>.fromValues(values);
       } else {
  -      return new _EnumSet<E>.fromValues(values);
  +      return _EnumSet<E>.fromValues(values);
       }
     }
   
  
positive.code:   EnumSet<E> removeAll(EnumSet<E> set) {
      int removed = _value & set.value;
      _value &= ~set.value;
      return new EnumSet<E>.fromValue(removed);
    }
  
    @override
  
negative.code: 
    @override
    String toString() {
      return value.toRadixString(2);
    }
  }
  
  