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Solution
Here punsihment is given forever once any of the player deviates. Hence there are two outcome possible for this subgame: (B, E) in for all periods including the current one or (C, F) in all periods as the punishment is given forever.
For the first case, player 1’s payoff is 7 for infinite period. If he deviates in first period he will be able to secure 8 in that period but will receive only 1 for each period forever. Hence the payoff is 8 + + 2 + ... = 8(1) + . The player has no incentive to deviate if the payoff from not deviating exceed the payoff from deviating:
7 8(1) +
7 8 8 +
7 8 – 7
1/7
For the second case, player 2\'s payoff is 5 for infinite period. If he deviates in first period he will be able to secure 8 in that period but will receive only 1 for each period forever. Hence the payoff is 8 + + 2 + ... = 8(1) + . The player has no incentive to deviate if the payoff from not deviating exceed the payoff from deviating:
5 8(1) +
5 8 8 +
5 8 – 7
3/7
Hence the correct option is 3/7. Option A is correct.
