docs: def _add_constraints(self, relation):
          """Add the given relation as one or more constraints.
  
          Return a list of the names of the constraints added.
          """
          names = []
          expression = relation.expression
          for value_set in expression.value_sets():
              name = next(self._constr_names)
              self._p.addConstr(
                  self._grb_expr_from_value_set(value_set),
                  self.CONSTR_SENSE_MAP[relation.sense],
                  -float(expression.offset), name)
              names.append(name)
  
          self._p.update()
  
          return names