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(a) Of three prisoners, call them 1, 2, and 3, two have been chosen by lot for execution. Prisoner 3 says to the guard, "Which of 1 and 2 is to be executed?

One of them will be, and you give me no information about myself in telling me which it is." The guard finds this reasonable and says, "Prisoner 1 is to be executed." And now 3 reasons, "I know that 1 is to be executed; the other will be either 2 or me, and so my chance of being executed is now only ;, instead of the { it was before," Apparently, the guard has given him information.