code: def i_logp(self, index):
          
          all_relevant_stochastics = set()
          p, i = self.stochastic_indices[index]
          try:
              return p.logp + logp_of_set(p.extended_children)
          except ZeroProbability:
              return -Inf
docs: Evaluates the log-probability of the Markov blanket of
          a stochastic owning a particular index.