This game is taken from Schelling's Game Theory: How to Make Decisions by R.V. Dodge, in which contenders practice brinksmanship to their own advantages. It goes as follows:
Anderson, Barnes, and Cooper are to fight a gun duel. They will stand close to one another, so that each can kill one of the others in one shot or deliberately miss. The first to fire will be chosen at random, and they will rotate in the order Anderson, Barnes, and Cooper, each firing one shot at a time.
If there is more than one survivor after a number of rounds, one of the contenders will be chosen at random and forced to kill one of the others, and this will be repeated if there is still more than one alive after a few more rounds.
Before the duel starts, Anderson may make any statement, followed by a statement from Barnes, and finally one from Cooper. They will adhere to the following rules:
- Statements are irrevocable. A contender may not act to contradict his statement.
- He will act in his own best interest when it does not conflict with Rule One.
- He will act randomly when it does not conflict with Rules One and Two.
There are referees to ensure that the rules are followed. If a contender commits himself to a mixed strategy (for example, to miss with a probability of 1/3), the probability will be determined objectively (by tossing dice, etc.).
Q1: What statement will Anderson make? What's his best strategy and his probability of surviving?
Q2: If three contenders are to make their statements in the order of ACB, what would be the best statement for Anderson?
Q3: If there're more than three contenders, does this game become simpler or more difficult? Can we say anything about the $N$ contenders case for $N\gt 3$?
Notice that if no one makes any statement, no one will shoot, and everyone has a surviving chance of 1/3. If only Anderson is allowed to make a statement, he can guarantee near certain survival by making this statement to B and C: "If you don't kill each other at your first opportunities, I will kill the first of you who fail to do so at my first opportunity; otherwise, I'll shoot at the survivor of you with 1% chance of missing."
In the book, a suggested best solution for Q1 is for A to say:"If B does not commit to unconditionally shooting C, I will shoot him." The argument is that B has no choice but to accept, because refusing A's proposal would result in certain death for B. But that is clearly erroneous! Because B can say: "If C doesn't promise to kill A at his first opportunity, I will kill C at mine; if C does, I will kill A at my first opportunity and shoot at C with 1% chance of missing if he kills A first." By refusing B's proposal C has 2/3 chance to survive (1/3 for A shooting first and 1/3 for C shooting first); by accepting he has 2/3+0.33% chance (1/3 for A shooting first, 1/3 for B shooting first and 0.33% for C shooting first). So C will accept. Then A is doomed, bound by his own inconvenient statement.