code: def prt_keys(self, prt, pre):
          
          prt.write('{PRE}Relationship to parent: {ABC}\n'.format(
              PRE=pre, ABC=''.join(self.rel2chr.values())))
          for rel, alias in self.rel2chr.items():
              prt.write('{PRE}    {A} {DESC}\n'.format(PRE=pre, A=alias, DESC=rel))
          prt.write('\n{PRE}Relationship to child: {ABC}\n'.format(
              PRE=pre, ABC=''.join(self.rev2chr.values())))
          for rel, alias in self.rev2chr.items():
              prt.write('{PRE}    {A} {DESC}\n'.format(PRE=pre, A=alias, DESC=rel))
docs: Print the alias for a relationship and its alias.