Election Safety: At most one leader can be elected in a given term. (§5.2)
Leader Append-Only: A leader never overwrites or deletes entries in its log; it only appends new entries. (§5.3)
Log Matching: If two logs contain an entry with the same index and term, then the logs are identical in all entries up through the given index. (§5.3)
Leader Completeness: If a log entry is committed in a given term, then that entry will be present in the logs of the leaders for all higher-numbered terms. (§5.4)
State Machine Safety: If a server has applied a log entry at a given index to its state machine, no other server will ever apply a different log entry for the same index. (§5.4.3)