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Topic: Past, Present, Future (Read 9410 times) |
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Rupert
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What if I ask Past first or Future last? Which question will they answer?
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jkemp
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Re: Past, Present, Future
« Reply #1 on: Jul 30th, 2002, 7:22pm » |
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I assumed that Past, if asked first, would say nothing; similarly, if I asked Future last, he would say nothing.
I believe I can identify Past Present & Future in only 2 questions.
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S. Owen
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Possible solution?
« Reply #2 on: Jul 30th, 2002, 7:50pm » |
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Yeah, I think this needs some clarification. If in fact Past/Future are silent in those cases, then you need just three of the same question: "Are you the god Present?"
Is this what you guys are thinking?
Ask one of them. If the god is silent, it's Past. The next to answer will tell you definitively which is Present, and thus Future.
If the first god answers, it is telling you whether it is Future or Past, essentially. If it's Future, same argument as above - next question gets it.
If the first god is Present, you need to ask two more. If the last god doesn't answer, it's Future, otherwise the second one was.
Now, regardless, I wonder what happens if we assume time is circular, whatever, and that Future will answer your *first* question if asked last, and Past will answer your last one if asked first. Then what? That's probably the intent.
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jkemp
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Re: Past, Present, Future
« Reply #3 on: Jul 30th, 2002, 8:02pm » |
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Assuming non-circular answers (i.e. Past and Future are silent when they can't answer), you can work it out in just two questions.
Ask god #1: "Are you Past?"
- Past would remain silent
- Present would say "No"
- Future would say "Yes" (see next question)
Ask god #2 (someone else than #1): "Are you Future?"
- Past would reply "Yes"
- Present would reply "No"
- Future would remain silent
By elimination two questions would allow you to determine who is who.
If the first god answers "No", you know he is Present. If the second god answers "Yes", you know he is Past, and the third god is Future. If the second god remains silent, you know he is Future, and the third god is Past.
If the first god answers "Yes", you know he is Future. If the second god answers "Yes", you know he is Past, and the third god is Present. If the second god answers "No", you know he is Present, and the third god is Past.
If the first god doesn't reply, you know he is Past. This means you have to change your second question to "Are you present?". If the second god replies "Yes", you know he is Present and the third god is Future. If the second god doesn't reply, you know he is Future and the third god is Present.
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william wu
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Re: Past, Present, Future UPDATE
« Reply #4 on: Jul 31st, 2002, 1:21pm » |
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This riddle has been updated by the creator, Eric Yeh, so that it is more clear. Note that the gods speak their own language -- they may not assign the same meaning to the word "Yes" that we do.
* * *
There are three omniscient gods sitting in a chamber: Past, Present and Future. They are all truthful, but with the following caveat: Present answers the question currently being asked, Past answers the last question asked in their chamber, and Future answers the next question which will be asked in their chamber. Furthermore, they answer in a language which no one else understands, so that while their "yes"'s and "no"'s are consistent amongst themselves, you do not know which is "yes" and which is "no". With three questions, you must determine which god is which.
Because of possible time conflicts, you must determine your questions ahead of time, rather than based on previous answers. You are, however, allowed to choose who you ask each of your three questions to dynamically, and scoping is also dynamic (e.g. the pronoun "you" in a question will always refer to the person you choose to ask the question to, not a predetermined person). No time related questions (e.g., "if the answer to my second question was 'no', then... otherwise ...") are permissible, as this could lead to paradoxes within the space-time continuum). Finally, note that if you ask Past your first question or Future your last question, the answer will give you no additional information because you do not know what the last or next questions are!
* * *
thanks eric 
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Eric Yeh
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Re: Past, Present, Future
« Reply #5 on: Jul 31st, 2002, 1:41pm » |
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Come on guys, you didn't think I'd make it that easy, did you?? Plus, I'd have to be a bit dense to not get it with two questions if they remained silent as described above. (Past, Present, Future II: How low would Eric's IQ have to be for him to need three questions to solve PPF I if interpreted as above? ) That's ok though -- since it is listed as an original riddle and none of you know me, it was fair enough to think it possible that I could be some total idiot. BUT, now that it's been properly and fully phrased, please let me know what you all think!!!!!
Happy puzzling,
Eric
eyeh@post.harvard.edu
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Aleksi Liimatainen
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I may have missed something, but this riddle seems impossible to be solved with yes/no-questions. It looks like there will always be some ambiguity left after you've asked the 3 questions, though I haven't been able to prove it.
Instead, I'll try to side-step the language barrier.
My solution fits the constraints given for the questions, but it might be considered cheating anyway
My solution:
The Questions:
"Please point at Future."
"Please point at Future."
"Please point at Present."
Ask the first two questions from the same person (call him A).
Call the first one he points at (besides himself) B. The third one is C.
If A points twice at a same person (not himself), that one is Future. Ask A the third one. If he is Past, he'll point at Future again. Present points at himself. The C is who's left.
If A points first at himself, then at someone else, he's either Past or Future. Future is either A or B. C can't be Future, so he must be Past or Present. Ask third question from C. If he points at himself, he is Present. Otherwise, he is Past and points at A, who is Future. Present is B.
In all other combinations of answers, A must be Past. Ignore his first answer. He answered the second question by pointing at Future. The one left is Present. Ask the third question from anyone you like, just to be sure you don't accidentally wreck the space-time continuum
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Eric Yeh
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Re: Past, Present, Future
« Reply #7 on: Aug 1st, 2002, 6:40am » |
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Sorry Aleksi, yes/no questions only.
If you finish your proof that there is no solution, I'll buy you dinner.
Good luck,
Eric
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bartleby
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Eric -
Do all the gods speak the same language? For example, if "foo" = "yes" for Past then all the gods will use "foo" for "yes"?
Do all the gods understand each other? For example, if I ask god #1 a question, and he answers "foo", then can I assume god #2 knows what answer god #1 gave, and what it means? (Although this probably isn't important, because I think you're trying to prevent questions like "God #2, would you answer the same as God #1 to the same question?")
Are we to assume that we are one questioner in a continuum of questioners, meaning that if I ask a question to god #1 who turns out to be Past, and he says "bleem", that "bleem" might be the answer to the last question the PREVIOUS questioner asked?
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bartleby
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Re: Past, Present, Future
« Reply #9 on: Aug 1st, 2002, 10:05am » |
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Eric,
Never mind about those first 2 questions in my previous post, they were stupid questions, of course the answers are "Yes" and "Doesn't matter", but the third question is still important.
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Eric Yeh
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Re: Past, Present, Future
« Reply #10 on: Aug 1st, 2002, 10:14am » |
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Bartleby,
1) You are correct that the first answer is "yes" -- that's what I meant by "consistent amongst themselves".
2) This would seem to be permissible to me. I think your parenthetical question is acceptable, actually, as long as it doesn't violate any of the timing aspects. Basically anything that would not be a paradox (in the vein of "this statement is false") would be allowed.
3) Yes, that was my intention, but I'm not sure I see the relevance. Can you explain further how it might affect the solution?
Best,
Eric
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bartleby
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Re: Past, Present, Future
« Reply #11 on: Aug 1st, 2002, 11:03am » |
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Eric,
The trouble I'm running into is that I've got a grid, there are 27 different permutations for the order that I question the gods. If there is another questioner questioning before me, and one after me, and I ask Past first, or Future last, I get an answer that is randomly "spoo" or "fleem". Not only do I not know what the answer means, I don't know if he's answering my question or not, so this multiplies out my decision grid in an ugly way... want to know if this is something I need to solve or not.
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bartleby
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Re: Past, Present, Future
« Reply #12 on: Aug 1st, 2002, 11:10am » |
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Eric -- Can I ask questions of the sort, "Are you answering the question that I am asking you right now?"?
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Eric Yeh
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Re: Past, Present, Future
« Reply #13 on: Aug 1st, 2002, 11:12am » |
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Bartleby,
Sure you can. But Present is the only one who would actually answer it (at this point in time).
Best,
Eric
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Aleksi Liimatainen
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Time-shifting questions?
« Reply #14 on: Aug 1st, 2002, 11:52pm » |
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Can you ask multi-part questions with different parts addressed to different deities?
Eg: "If you are Past, are you Past, or, if you are Present, is the one on your left Future, or, if you are Future, is the one on your right Present?"
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Eric Yeh
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Re: Past, Present, Future
« Reply #15 on: Aug 2nd, 2002, 5:32am » |
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Aleksi,
Sure, I suppose there's nothing about that construct that would make it illegal. Of course, it would still be subject to the time-shifting, so for example in your question below, "if you are past, are you past" is equivalent to "are you past".
But note that as in most of the truth-teller genre of puzzles, a truly elegant solution uses very few if any such conditions.
Best,
Eric
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icon
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Re: Past, Present, Future
« Reply #16 on: Aug 2nd, 2002, 5:59am » |
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hehe this 1 is lot harder than 2 road guys
problem is this: u need probably to ask least 1 question to each person and my guess 1 be enough
this has to follow strong logic in my view since you would have to assume lot of things and follow same logic to be successfull
now i didnt get this 1 yet but am thinking what can be said :>
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Eric Yeh
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Re: Past, Present, Future
« Reply #17 on: Aug 2nd, 2002, 6:13am » |
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Phshew! At least we're more in agreement on this thread `:)
;)
(Hey Will, why no automated sweat smiley??)
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Jonathan the Red
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Re: Past, Present, Future
« Reply #18 on: Aug 2nd, 2002, 5:06pm » |
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Request for clarification:
God A is Present, God B is Past, God C is Future. Splunge means "yes", Fleen means "no."
I ask God A: "Are you Past?" He answers "Fleen."
I then ask God B: "Will the world ever be freed from the scourge of Carrot Top?" or some other question; it doesn't matter, because he's gonna answer the question I asked God A.
The question is: does he answer "Splunge" because that's the correct answer to "Are you Past?", or does he answer "Fleen" because that's the correct answer to "Is God A Past?"
The problem specifies "dynamic scoping", so I suspect the former, but want to make sure.
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Eric Yeh
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Re: Past, Present, Future
« Reply #19 on: Aug 2nd, 2002, 5:29pm » |
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Splunge me, baby.
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Jonathan the Red
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Re: Past, Present, Future
« Reply #20 on: Aug 2nd, 2002, 7:05pm » |
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What an awesome puzzle! Got a solution, but I must admit I cheated:
(in black to prevent spoilage):
First off, the bit about the different language is a very minor hurdle. For any proposition P, you can ask someone: "Does 'splunge' mean 'yes' if and only if P?" The answer to this question will be 'splunge' if P is true, 'fleen' if it isn't. For the remainder of my solving effort, I'll be pretending the Gods answer Yes or No.
Label the Gods A, B, and C.
Question 1: Is God A Past? -- directed to God A
Question 2: Is God A not Past? -- directed to God B
Question 3: Are you Future? -- directed to God C if the answer to question #2 is Yes, to God B otherwise
The proof is left as an exercise for the reader Many other solutions exist. All of them require at least one "conditional" question... that is, a question that will be directed at a different God depending on the last answer.
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Eric Yeh
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Re: Past, Present, Future
« Reply #21 on: Aug 2nd, 2002, 7:13pm » |
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Thanks dude!!! Glad you enjoyed it!!!!!  But what do you mean you "cheated"? Since very few people in the world have seen this problem thus far, there aren't many ways you can hack a solution!!!
(I'll check your soln in a sec...)
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Eric Yeh
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Re: Past, Present, Future
« Reply #22 on: Aug 2nd, 2002, 7:30pm » |
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(Ok, sorry, just had to finish something on the phone there.)
Yep, your soln works -- very elegant!!
But you're giving away my secret about the language barrier, o no! 
And yes, there are plenty of solns, and they do all require that dynamic portion. Too bad -- it would be cool if there were a static one. But I guess you and I know why that cannot be.
BUT, it's still a good exercise for the arbitrary reader to figure out why the dynamic question is required, so if you're a new reader... go for it!!!
Best,
Eric
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Jonathan the Red
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Re: Past, Present, Future
« Reply #23 on: Aug 3rd, 2002, 9:10pm » |
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Quote:But what do you mean you "cheated"? Since very few people in the world have seen this problem thus far, there aren't many ways you can hack a solution!!!
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Well, it depends on the definition of "cheated." I, er, wrote a computer program to brute-force the solution. The one I posted was the very first solution it came up with; other solutions it found are much more elegant. I can post them if there's any interest.
So is that "cheating?" Some would say that it is... the problem is intended to be solved using logical reasoning and having a computer brute-force its way to a solution circumvents that. Others would say that I had to use my brain to devise a computer program that would do the job, so it wasn't really cheating.
It's a philosophical point that can probably never truly be answered, but I tend to lean toward calling it cheating.
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Eric Yeh
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Re: Past, Present, Future
« Reply #24 on: Aug 3rd, 2002, 9:34pm » |
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Intriguing!!! I wouldn't have thought this would be a very computer solvable problem!! In fact, part of my intention when devising it was in particular to avoid using "the usual" algorithm for solving these truth-teller questions.
I'm very curious to hear more about the program, although maybe this isn't the right forum for it. I can't think how I'd plan such a program myself, in fact. I'd be impressed if your program could proveably guarantee finding the answer to similar problems, if they exist...
Best,
Eric
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