<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _get_pooler(self, units, prefix):
 """ Construct pooler. The pooler slices and projects the hidden output of first token in the sequence for segment level classification. """

        with self.name_scope():
            pooler = nn.Dense(units=units, flatten=False, activation='tanh',
                              prefix=prefix)
        return pooler