code: def delete_relation(self, src, relation, target):
          ''' can be both used as (src, relation, dest) for a single relation or
              (src, relation) to delete all relations of that type from the src '''
          self.__require_string__(relation)
          if src in self and target in self:
              self._get_item_node(src).unlink(relation, self._get_item_node(target)f delete_relation(self, src, relation, target):
          ''' can be both used as (src, relation, dest) for a single relation or
              (src, relation) to delete all relations of that type from the src '''
          self.__require_string__(relation)
          if src in self and target in self:
              self._get_item_node(src).unlink(relation, self._get_item_node(target))
docs: can be both used as (src, relation, dest) for a single relation or
              (src, relation) to delete all relations of that type from the src