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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def mirror(self: BaseBoardT) -> BaseBoardT: """ 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. """

        board = self.transform(flip_vertical)
        board.occupied_co[WHITE], board.occupied_co[BLACK] = board.occupied_co[BLACK], board.occupied_co[WHITE]
        return board