code: def mirror(self: BaseBoardT) -> BaseBoardT:
          
          board = self.transform(flip_vertical)
          board.occupied_co[WHITE], board.occupied_co[BLACK] = board.occupied_co[BLACK], board.occupied_co[WHITE]
          return board
docs: Returns a mirrored copy of the board.
  
          The board is mirrored vertically and piece colors are swapped, so that
          the position is equivalent modulo color.