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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 receive_delivered(self, delivered: Delivered):
 """ Handle a Delivered message. The Delivered message is how the UDP transport guarantees persistence by the partner node. The message itself is not part of the raiden protocol, but it's required by this transport to provide the required properties. """

        self.raiden.on_message(delivered)

        message_id = delivered.delivered_message_identifier
        async_result = self.raiden.transport.messageids_to_asyncresults.get(message_id)

        # clear the async result, otherwise we have a memory leak
        if async_result is not None:
            del self.messageids_to_asyncresults[message_id]
            async_result.set()
        else:
            self.log.warn(
                'Unknown delivered message received',
                message_id=message_id,
            )