1. Alice sends message to Bob to attack on Tuesday and 9am
2. Bob sends message to Alice confirming this is fine
3. Alice sends confirmation of confirmation to Bob
4. Bob sends confirmation of confirmation confirmation to Alice
5. Alice sends confirmation of the confirmation of the confirmation confirmation to Bob
But at this point, Bob has realized there is a confirmation. Alice has realized there is a confirmation also. Surely this is sufficient?
Alice and Bob must each choose an actual policy for how many confirmations they need before they actually commit to attack. We can number the messages like this:
1. Alice's first message 2. Bob's first message 3. Alice's second message 4. Bob's second message ...
Alice's policy can only commit to attack after receiving some even-indexed message n. Bob can only commit to attack after receiving some odd-indexed message m. So n and m cannot possibly be equal. Therefore the possibility exists that a message fails between n and m, and either Alice or Bob ends up attacking without the other's support.