Section 3.2.1 The Ordering of Decrees
Even with a leader, multiple nodes may temporarily believe they are president, which can lead to concurrent ballots. However, the protocol ensures that the ordering of important decrees remains correct despite this concurrency.
The Ordering of Decrees Balloting could take place concurrently for many different decree numbers, with ballots initiated by different legislators—each thinking he was president when he initiated the ballot. We cannot say precisely in what order decrees would be passed, especially without knowing how a president was selected. However, there is one important property about the ordering of decrees that can be deducedLAMPORT, P. 16 — §3.2.1
A decree was said to be proposed when it was chosen by the president in step 3 of the corresponding instance of the Synod protocol. The decree was said to be passed when it was written for the first time in a ledger. Before a president could propose any new decrees, he had to learn from all the members of a majority set what decrees they had voted for. Any decree that had already been passed must have been voted for by at least one legislator in the majority set. Therefore, the president must have learned about all previously passed decrees before initiating any new decree. The president would not fill a gap in the ledgers with an important decree—that is, with any decree other than the "olive-day" decree. He would also not propose decrees out of order. Therefore, the protocol satisfied the following decree-ordering property.
If decrees A and B are important and decree A was passed before decree B was proposed, then A has a lower decree number than B.
Despite concurrent ballots, safety and order are preserved.
Before proposing any new decrees, a president must learn which decrees have already been passed from a majority of legislators. This ensures no previously passed decree is skipped or reordered.
If a gap exists in the ledger, the president fills it with a special "olive-day" decree, ensuring continuity without disrupting the order of important decrees. These gaps can only exist if said numbered decrees never met quorum due to partition or other failures.
Before a president could propose any new decrees, he had to learn from all the members of a majority set what decrees they had voted for. Any decree that had already been passed must have been voted for by at least one legislator in the majority set.