code: def directed_account(transition, direction, mechanisms=False, purviews=False,
                       allow_neg=False):
      
      if mechanisms is False:
          mechanisms = utils.powerset(transition.mechanism_indices(direction),
                                      nonempty=True)
      links = [
          transition.find_causal_link(direction, mechanism, purviews=purviews,
                                      allow_neg=allow_neg)
          for mechanism in mechanisms]
  
      # Filter out causal links with zero alpha
      return DirectedAccount(filter(None, links))
docs: Return the set of all |CausalLinks| of the specified direction.