(Adapted from Pearl (1988)) Three prisoners, A, B, and C, are locked in their cells. It is common knowledge that one of them will be executed the next day and the others pardoned. Only the governor knows which one will be executed. Prisoner A asks the guard a favor. “Please ask the governor who will be executed, and then take a message to one of my friends B or C to let him know that he will be pardoned in the morning.” The guard agrees, and comes back later and tells A that he gave the pardon message to B. What are A’s chances of being executed, given this information? (Answer this mathematically, not by energetic waving of hands.)

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