code: def rectify_pi(self):
          
          if self.prior_information.shape[0] == 0:
              return
          self._parse_pi_par_names()
          adj_names = self.adj_par_names
          def is_good(names):
              for n in names:
                  if n not in adj_names:
                      return False
              return True
          keep_idx = self.prior_information.names.\
              apply(lambda x: is_good(x))
          self.prior_information = self.prior_information.loc[keep_idx,:]
docs: rectify the prior information equation with the current state of the
          parameter_data dataframe.  Equations that list fixed, tied or missing parameters
          are removed. This method is called during Pst.write()