I got this problem from Rustan Leino, who got it from Sophia Drossopoulou.
I solved it and wrote up my solution.
100 coins are to be distributed among some number of persons, referred to by the labels A, B, C, D, .... The distribution works as follows. The person with the alphabetically highest label (for example, among 5 people, E) is called the chief. The chief gets to propose a distribution of the coins among the persons (for example, chief E may propose that everyone get 20 coins, or he may propose that he get 100 coins and the others get 0 coins). Everyone (including the chief) gets to vote yes/no on the proposed distribution. If the majority vote is yes, then that's the final distribution. If there's a tie (which there could be if the number of persons is even), then the chief gets to break the tie. If the majority vote is no, then the chief gets 0 coins and has to leave the game, the person with the alphabetically next-highest name becomes the new chief, and the process to distribute the 100 coins is repeated among the persons that remain. Suppose there are 5 persons and that every person wants to maximize the number of coins that are distributed to them. Then, what distribution should chief E propose?
Chief E should propose the distribution $\langle A:1, B:0, C:1, D:0, E:98 \rangle.$ This sounds greedy, but it will work for the following reason.
First, let's determine what will happen if we get down to two players left: A and B. In this case, B should propose $\langle A:0, B:100 \rangle$ because B can vote for it and make it pass unilaterally.
We can now figure out what will happen if we get down to three players left: A, B, and C. In this case, C should propose $\langle A:1, B:0, C:99 \rangle.$ A will vote for this because he knows that if this vote fails the previous paragraph's scenario will occur and he will get nothing. Since A and C vote for it, it succeeds.
We can now figure out what will happen if we get down to four players left: A, B, C, and D. In this case, D should propose $\langle A:0, B:1, C:0, D:99 \rangle.$ B will vote for this because he knows that if this vote fails the previous paragraph's scenario will occur and he will get nothing. Since B and chief D vote for it, it succeeds.
Now, finally, we can see why E should propose $\langle A:1, B:0, C:1, D:0, E:98 \rangle.$ He can count on the votes of A and C because if this vote fails they both get nothing. With the votes of A, C, and E, the vote will pass. It's good to be the chief!