This puzzle is taken from Schelling's Game Theory: How to Make Decisions by R.V. Dodge, in which bargaining power is gained, paradoxically, by burning bridges and removing options for oneself. Here it goes:
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 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 required to shoot one of the others, and this will be repeated if there is still more than one alive.
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:
- 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 choice of action on a statistical basis (for example, if Anderson commits himself to miss with a probability of 1/3), the choice 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?
Warmup example 1: What happens when no one makes a statement?
If no one makes any statement, it would be foolish for a contender to shoot, because he's going to be shot by the other remaining player. So everyone just wait out a number of rounds, let the referees randomly choose one and force him to shoot, hoping to be the survivor under his gun. By Rule Three, this shooter will randomly shoot one of the other two contenders. So if you're not chosen as the shooter, you have 1/2 chance to survive. All in all, when no one speaks, each one has a survival probability of 1/3.
Warmup example 2: What happens when only Anderson is allow to make a statement?
A can guarantee near certain victory 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 the survivor of you with 1% chance of missing." If C fires first, he'll be dead if he doesn't kill B; if he does kill B, he'll have 1% survival chance. So C will kill B. Similarly, if B fires first, his only chance (also 1%) to live is to kill C. If A fires first he'll shoot in the air and let B kill C. All in all, A has 99.33% chance to survive, B and C each have 0.33% percent, ignoring rounding error.
Hint (I decide to give this hint because I'm tired of trying to convince people about the flaws in their answers. Major spoilers inside.)
The originator of this puzzle, Nobel Laureate Thomas Schelling himself, was able to gave what he thought was a best answer he could think of for Q1, in which Anderson achieves a certain surviving probability less than 90%. Although there's no proof that his is the best, You should check really carefully if you think you find a way to give Anderson a surviving chance close to 100%.