code: def _set_mixed_moments_to_zero(self, closed_central_moments, n_counter):
          r
  
          positive_n_counter = [n for n in n_counter if n.order > 1]
          if self.is_multivariate:
              return closed_central_moments
          else:
              return [0 if n.is_mixed else ccm for n,ccm in zip(positive_n_counter, closed_central_moments)]
docs: r"""
          In univariate case, set the cross-terms to 0.
  
          :param closed_central_moments: matrix of closed central moment
          :param n_counter: a list of :class:`~means.core.descriptors.Moment`\s representing central moments
          :type n_counter: list[:class:`~means.core.descriptors.Moment`]
          :return:  a matrix of new closed central moments with cross-terms equal to 0