Eventual Common Knowledge

When message communication time is not small, as in ε-coordination, and messages are delayed for a long period, it it still possible to plan a coordinated attack. We call this way of coordination eventual coordination. When a message has been sent to a group of agents, every member of the group receives this message at a certain point in time, and the agent knows, that every other agent in the group will eventually receive the message. This might be in past, present or future time.
 
We call the knowledge that is attained eventual common knowledge. ε-Coordination and eventual coordination are both a weakening of the simultaneity requirement of a coordinated attack. But it is still possible to coordinate the attack. If you take a look at the Byzantine Generals problem again: if one of the two divisions sends a message "Attack!", and the communication medium is reliable this time, then the attacking division knows that at some point in time, the other division will attact too. This is a well coordinated attack (but the regiments probably will not survive the battle).
 

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