code: def set_object(self, obj, properties):
          
          self._objects.add(obj)
          properties = set(properties)
          self._properties |= properties
          pairs = self._pairs
          for p in self._properties:
              if p in properties:
                  pairs.add((obj, p))
              else:
                  pairs.discard((obj, p))
docs: Add an object to the definition and set its ``properties``.