Lost messages (Exercise 5.7)
I'm having some trouble understanding the concept of lost messages. The current notion I have ist that a message is lost if it was received by a process p, but is not kept, since this process has to roll back to a state prior to the reception.
My question is now (for exercise 5.7):
Why is M3 not a lost message, if a Crash at position B occurs? I seem to remember it has sth to do with P2 not having a checkpoint after send, but I do not quite get it.