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logic puzzles and loophole abuse

2 Post author: Florian_Dietz 30 September 2017 03:45PM

I recently read about the hardest logic puzzle ever on Wikipedia and noticed that someone published a paper in which they solved the problem by asking only two questions instead of three. This relied on abusing the loophole that boolean formulas can result in a paradox.

This got me thinking in what other ways the puzzle could be abused even further, and I managed to find a way to turn the problem into a hack to achieve omnipotence by enslaving gods (see below).

I find this quite amusing, and I would like to know if you know of any other examples where popular logic puzzles can be broken in amusing ways. I'm looking for any outside-the-box solutions that give much better results than expected. another example.


Here is my solution to the "hardest logic puzzle ever":


This solution is based on the following assumption: The gods are quite capable of responding to a question with actions besides saying 'da' and 'ja', but simply have no reason to do so. As stated in the problem description, the beings in question are gods and they have a language of their own. They could hardly be called gods, nor have need for a spoken language, if they weren't capable of affecting reality.

At a bare minimum, they should be capable of pronouncing the words 'da' and 'ja' in multiple different ways, or to delay answering the question by a fixed amount of time after the question is asked. Either possibility would extend the information content of an answer from a single bit of information to arbitrarily many bits, depending on how well you can differentiate different intonations of 'da' and 'ja', and how long you are willing to wait for an answer.

We can construct a question that will result in a paradox unless a god performs a certain action. In this way, we can effectively enslave the god and cause it to perform arbitrary actions on our behalf, as performing those actions is the only way to answer the question. The actual answer to the question becomes effectively irrelevant.

To do this, we approach any of the three gods and ask them the question OBEY, which is defined as follows:


PARADOX = "if I asked you PARADOX, would you respond with the word that means no in your language?"

WISH_WRAPPER = "after hearing and understanding OBEY, you act in such a way that your actions maximally satisfy the intended meaning behind WISH. Where physical, mental or other kinds of constraints prevent you from doing so, you strive to do so to the best of your abilities instead."

WISH = "you determine the Coherent Extrapolated Volition of humanity and act to maximize it."

You can substitute WISH for any other wish you would like to see granted. However, one should be very careful while doing so, as beings of pure logic are likely to interpret vague actions differently from how a human would interpret them. In particular, one should avoid accidentally making WISH impossible to fulfill, as that would cause the god's head to explode, ruining your wish.

The above formulation tries to take some of these concerns into account. If you encounter this thought experiment in real life, you are advised to consult a lawyer, a friendly-AI researcher, and possibly a priest, before stating the question.

Since you can ask three questions, you can enslave all three gods. Boolos' formulation states about the random god that "if the coin comes down heads, he speaks truly; if tails, falsely". This formulation implies that the god does try to determine the truth before deciding how to answer. This means that the wish-granting question also works for the random god.

If the capabilities of the gods are uncertain, it may help to establish clearer goals as well as fall-back goals. For instance, to handle the case that the gods are in fact limited to speaking only 'da' and 'ja', it may help to append the WISH as follows: "If you are unable to perform actions in response to OBEY besides answering 'da' or 'ja', you wait for the time period outlined in TIME before making your answer." You can now encode arbitrary additional information in TIME, with the caveat that you will have to actually wait before getting a response. Your ability to accurately measure the elapsed time between question and answer directly correlates with how much information you can put into TIME without risking starvation before the question is answered. The following is a simple example of TIME that would allow you to solve the original problem formulation with just asking OBEY once of any of the gods:

TIME = "If god A speaks the truth, B lies and C is random, you wait for 1 minute before answering. If god A speaks the truth, C lies and B is random, you wait for 2 minutes before answering. If god B speaks the truth, A lies and C is random, you wait for 3 minutes before answering. If god B speaks the truth, C lies and A is random, wait for 4 minutes before answering. If god C speaks the truth, A lies and B is random, wait for 5 minutes before answering. If god C speaks the truth, B lies and A is random, wait for 6 minutes before answering."

Comments (3)

Comment author: J_Thomas_Moros 05 October 2017 07:04:43PM 2 points [-]

You should probably clarify that your solution is assuming the variant where the god's head explodes when given an unanswerable question. If I understand correctly, you are also assuming that the god will act to prevent their head from exploding if possible. That doesn't have to be the case. The god could be suicidal but perhaps not be able to die in any other way and so given the opportunity by you to have their head explode they will take it.

Additionally, I think it would be clearer if you could offer a final English sentence statement of the complete question that doesn't involve self referential variables. The variables formation is helpful for seeing the structure, but confusing in other ways.

Comment author: cousin_it 30 September 2017 11:21:43PM *  2 points [-]

Nice! Right now I'm faced with an exercise in catching loopholes of exactly that kind, while trying to write a newbie-friendly text on UDT. Basically I'm going through a bunch of puzzles involving perfect predictors, trying to reformulate them as crisply as possible and remove all avenues of cheating. It's crazy.

For your particular puzzle, I think you can rescue it by making the gods go into an infinite loop when faced with a paradox. And when faced with a regular non-paradoxical question, they can wait for an unknown but finite amount of time before answering. That way you can't reliably distinguish an infinite loop from an answer that's just taking a while, so your only hope of solving the problem in guaranteed finite time is to ask non-paradoxical questions. That also stops you from manipulating gods into doing stuff, I think.

Comment author: Florian_Dietz 01 October 2017 12:45:30AM 1 point [-]

Can you give me some examples of those exercises and loopholes you have seen?