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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 _uniq(self):
 """ Create a list of all the pixels that cover this region. This list contains overlapping pixels of different orders. Returns ------- pix : list A list of HEALPix pixel numbers. """

        pd = []
        for d in range(1, self.maxdepth):
            pd.extend(map(lambda x: int(4**(d+1) + x), self.pixeldict[d]))
        return sorted(pd)