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:       // constant empty set together with mutable sets where applicable.
        return set.clone();
      }
      throw new UnsupportedError('EnumSet.removeAll');
    }
  }
  
  
negative.code: 
    /// Create a set containing the [values]. If [fixed] is `true` the set is
    /// immutable.
    factory EnumSet.fromValues(Iterable<E> values, {bool fixed = false}) {
      if (fixed) {
        return _ConstEnumSet<E>.fromValues(values);
      } else {
        return _EnumSet<E>.fromValues(values);
      }
    }
  
  