def propose_value(self, key, value, assume_leader=False):
        """
        Starts new Paxos aggregate and proposes a value for a key.

        Decorated with retry in case of notification log conflict
        or operational error.
        """
        assert isinstance(key, UUID)
        paxos_aggregate = PaxosAggregate.start(
            originator_id=key,
            quorum_size=self.quorum_size,
            network_uid=self.name
        )
        msg = paxos_aggregate.propose_value(value, assume_leader=assume_leader)
        while msg:
            msg = paxos_aggregate.receive_message(msg)
        new_events = paxos_aggregate.__batch_pending_events__()
        self.record_process_event(ProcessEvent(new_events))
        self.repository.take_snapshot(paxos_aggregate.id)
        self.publish_prompt()
        return paxos_aggregate
Starts new Paxos aggregate and proposes a value for a key.

        Decorated with retry in case of notification log conflict
        or operational error.