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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 _dedup_index(self, df_a):
 """Build an index for deduplicating a dataset. Parameters df_a : (tuple of) pandas.Series The data of the DataFrame to build the index with. Returns ------- pandas.MultiIndex A pandas.MultiIndex with record pairs. Each record pair contains the index values of two records. The records are sampled from the lower triangular part of the matrix. """

        pairs = self._link_index(df_a, df_a)

        # Remove all pairs not in the lower triangular part of the matrix.
        # This part can be inproved by not comparing the level values, but the
        # level itself.
        pairs = pairs[pairs.labels[0] > pairs.labels[1]]

        return pairs