def reduce_slice(self, start, end, options=None):
        """
        Adds the Javascript built-in ``Riak.reduceSlice`` to the
        query as a reduce phase.

        :param start: the beginning of the slice
        :type start: integer
        :param end: the end of the slice
        :type end: integer
        :param options: phase options, containing 'language', 'keep'
          flag, and/or 'arg'.
        :type options: dict
        """
        if options is None:
            options = dict()

        options['arg'] = [start, end]
        return self.reduce("Riak.reduceSlice", options=options)
Adds the Javascript built-in ``Riak.reduceSlice`` to the
        query as a reduce phase.

        :param start: the beginning of the slice
        :type start: integer
        :param end: the end of the slice
        :type end: integer
        :param options: phase options, containing 'language', 'keep'
          flag, and/or 'arg'.
        :type options: dict