<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def handle_nested_relation(self, line: str, position: int, tokens: ParseResults):
 """Handle nested statements. If :code:`allow_nested` is False, raises a ``NestedRelationWarning``. :raises: NestedRelationWarning """

        if not self.allow_nested:
            raise NestedRelationWarning(self.get_line_number(), line, position)

        self._handle_relation_harness(line, position, {
            SUBJECT: tokens[SUBJECT],
            RELATION: tokens[RELATION],
            OBJECT: tokens[OBJECT][SUBJECT],
        })

        self._handle_relation_harness(line, position, {
            SUBJECT: tokens[OBJECT][SUBJECT],
            RELATION: tokens[OBJECT][RELATION],
            OBJECT: tokens[OBJECT][OBJECT],
        })
        return tokens