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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _handle_relation_harness(self, line: str, position: int, tokens: Union[ParseResults, Dict]) -> ParseResults: """Handle BEL relations based on the policy specified on instantiation. Note: this can't be changed after instantiation! """

        if not self.control_parser.citation:
            raise MissingCitationException(self.get_line_number(), line, position)

        if not self.control_parser.evidence:
            raise MissingSupportWarning(self.get_line_number(), line, position)

        missing_required_annotations = self.control_parser.get_missing_required_annotations()
        if missing_required_annotations:
            raise MissingAnnotationWarning(self.get_line_number(), line, position, missing_required_annotations)

        self._handle_relation(tokens)
        return tokens