What if you said that Bob and Alice have an agreement to send letters every 2 minutes (taking turns one after another). If Eve were to drop a message, Bob or Al

What if you said that Bob and Alice have an agreement to send letters every 2 minutes (taking turns one after another). If Eve were to drop a message, Bob or Alice would know that the message was discarded because the next sent message would not arrive in that 2-minute frame. Therefore, they do not update their state. If a state change is requested by either party, if and only if, simultaneous/consecutive messages go through (a total time of 4 minutes: one send and acknowledge) - states are updated: except the catch is that the send note contains the future time both Alice and Bob need to perform the update - which is constant in this entire exchange.