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Subject: "A puzzle of identical twins"     Previous Topic | Next Topic
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Liliya (Guest)
guest
Aug-02-01, 09:59 PM (EST)
 
"A puzzle of identical twins"
 
   I read the puzzle of identical twins and I don't think I understand all parts of it.

There are 2 identical twins, one always tells the truth and the other one who always lies. The truth teller is accurate in all his belief, but the lying brother is totally inaccurate in his beliefs.

When we ask both of them the same question, they both give the same answer, which means they both are telling the truth. It's just that one of them has mixed up mind and thinks that he lies about everything, but in real he is also telling the truth.
Now, calling him a liar wouldn't be true, because even though he thinks wrong and says the opposite, he's still telling the truth.
But, when we ask him if he is the accurate truth teller, and he says "no"- wouldn't really be true, because he is telling the truth to the other questions. The answer "no" would be true just for the people who think that that's the answer from a person they think has problems with his head.

If they both are telling the truth, then why would you want to find the liar??

I would appreciate if someone tell me if I'm thinking right.
Thanks.


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  Subject     Author     Message Date     ID  
  RE: A puzzle of identical twins alexb Aug-03-01 1
     RE: A puzzle of identical twins Liliya (Guest) Aug-03-01 2
         RE: A puzzle of identical twins alexb Aug-03-01 3
             RE: A puzzle of identical twins Liliya (Guest) Aug-03-01 4
                 RE: A puzzle of identical twins alexb Aug-03-01 5
                     RE: A puzzle of identical twins Liliya (Guest) Aug-04-01 6
  RE: A puzzle of identical twins Liliya (Guest) Aug-19-01 7
     RE: A puzzle of identical twins alexb Aug-19-01 8

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alexb
Charter Member
672 posts
Aug-03-01, 10:14 AM (EST)
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1. "RE: A puzzle of identical twins"
In response to message #0
 
   >I read the puzzle of identical
>twins and I don't think
>I understand all parts of
>it.

I believe you understood the puzzle well enough to pose a very valid question about it.

>Now, calling him a liar wouldn't
>be true, because even though
>he thinks wrong and says
>the opposite, he's still telling
>the truth.

Right. People are not judged by their thoughts, but by their actions. In so far as two people outwardly behave the same, they should be given an equal treatment in any court of law.

>If they both are telling the
>truth, then why would you
>want to find the liar??

In truth, there seldom exists a good reason for us to do what we are doing, not to mention mathematicians who get paid mostly for doing unreasonable things.

>I would appreciate if someone tell
>me if I'm thinking right.

Seriously, you are absolutely right. We can't call a fellow a liar who only tells truth.

But forget for a moment about the reality and try to think about the abstraction that Smullyan might have had in mind.

Or, think of the following scenario. Two boys were born - one a truth teller and the other a liar. They played and grew together and for a long while they were what they were destined to be, an honest man and a liar. The honest brother was loved and esteemed, the liar was despised and unhappy. He suffered terribly, especially mentally. Not yet 30, he suffered a stroke, from which he recovered fully physically, but not mentally. One of the results of the illness was that he completely lost confidence in his beliefs. At some point afterwards, he decided to reverse any spontaneous response of his. The moment he feels a desire to say something, he will now say the opposite.

It rains. Does it rain now?
Thinks yes, has an impulse to say no, says yes.

Is this tomato blue?
Thinks no, has an impulse to say yes, says no.

Are you a truth teller?
Thinks no, has an impulse to say yes, says no.

How does it'sound to you?


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Liliya (Guest)
guest
Aug-03-01, 02:43 PM (EST)
 
2. "RE: A puzzle of identical twins"
In response to message #1
 
   Thanks Mr.Alex for replying. I appreciate it.

One of the results of the illness was that he completely lost confidence in his beliefs. At some point afterwards, he decided to reverse any spontaneous response of his. The moment he feels a desire to say something, he will now say the opposite.

Ok. If that's what really happened, how would we know about it? I don't think that person would go and tell other people what he thinks he's doing, because he wants to lie and he doesn't want other people to know that he is.

Am I right??


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alexb
Charter Member
672 posts
Aug-03-01, 03:00 PM (EST)
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3. "RE: A puzzle of identical twins"
In response to message #2
 
   > Ok. If that's what really happened,
> how would we know about it?

But it's just a story, and it's our story at that. I am telling you this story, and you ask me how could I know.

To make my story more palatable, I can add another line. I was the nurse who delivered the boys. As the result, I developed an attachment to the boys, as well as to the mother, who was a single mom too. So we stayed friends after they left the hospital.

The time went by. I continued in my job which paid for my graduate studies and eventually landed a job in a mental clinic. When the liar boy - now a grown up fellow - felt sick, his mother - now my dear friend - sought my advice. So I was in a position to observe the said change in boy's behavior.

In fact, the change was not that sudden. The boy, while in the hospital, began experiencing doubts about his beliefs and shared the doubts with me, his doctor.

> I don't think that person would go
> and tell other people what he thinks
> he's doing

Right, in my story he does no such thing. He only answers questions when asked.

> because he wants to lie and he doesn't
> want other people to know that he is

No, as far as I understand - or rather remember - our conversations, they boy did not care about what other people think, not a little bit. From the birth on and especially after his illness, he was absolutely preoccupied with his own thoughts. He still is.


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Liliya (Guest)
guest
Aug-03-01, 10:13 PM (EST)
 
4. "RE: A puzzle of identical twins"
In response to message #3
 
   >they boy did not care about what other people think, not a little bit

I don't think the problem said anything about that. But I agree with you.
Still, if both boys were telling the truth then you can't really ask them if they are the truth tellers. What you should ask is if they are crazy or not, and they'll tell you the truth.

Thanks for responding, and sorry for waisting your time.


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alexb
Charter Member
672 posts
Aug-03-01, 10:27 PM (EST)
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5. "RE: A puzzle of identical twins"
In response to message #4
 
   >>they boy did not care about
>>what other people think, not a little bit
>
>I don't think the problem said
>anything about that.

You are right. I was just trying to come up with a background story for Smullyan's puzzle. That's all.

>But I
>agree with you.

No, no. It's I who agree with you.

>Still, if both boys were telling
>the truth then you can't
>really ask them if they
>are the truth tellers. What
>you should ask is if
>they are crazy or not,
>and they'll tell you the
>truth.

Well, I did ask what I asked.

>Thanks for responding, and sorry for
>waisting your time.

I am sorry you said that. No one can waste my time, but I myself. And no one can force me into correspondence against my will.

You brought up a very valid question, a question that I have overlooked. My first reaction was to just raise my arms and plead guilty. But then the story came up.

The point of the puzzle was not so much to fit the reality as to create a situation in which the same question is not in fact the same. With my bent of mind I never so much as stopped to think as to what made the second fellow a liar when in fact he always was telling truth.

I was very much satisfied with our correspondence, which also served as a nice dinner topic today. Thank you for providing me with an opportunity.

I had no intention of offending you. Please loosen up. The puzzle had a point, and for me this is what was important about it. But different people see the same thing with different eyes. By inventing the story I was trying to refocus your attention to that abstraction that Smullyan had in mind. That's all.


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Liliya (Guest)
guest
Aug-04-01, 12:28 PM (EST)
 
6. "RE: A puzzle of identical twins"
In response to message #5
 
   >I am sorry you said that.

I'm very sorry I made you feel that way, I didn't mean to.

>I had no intention of offending you.

You never did. It would be really hard to offend me even if you tried.

>But different people see the same thing with different eyes.

That's very true. Sometime I don't think about the answer to the puzzle as much as I think about the puzzle itself. I know my points of view will change, because I'm just 14 and I still have lots to learn.

I'm sorry if I sounded mean at some points, I didn't mean to.

Thanks a lot for your time.


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Liliya (Guest)
guest
Aug-19-01, 02:55 PM (EST)
 
7. "RE: A puzzle of identical twins"
In response to message #0
 
   Hello Mr.Alex.

I was thinking about this puzzle again.

The "liar's" answers to the questions are accurate, right?
When we ask him if he's the accurate truth teller, he is (because he's always telling the truth), but he thinks that he's not, but then lies about it and says "YES" (which again is true).

Am I right?
What do you think?

-Liliya


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alexb
Charter Member
672 posts
Aug-19-01, 03:06 PM (EST)
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8. "RE: A puzzle of identical twins"
In response to message #7
 
   LAST EDITED ON Aug-19-01 AT 03:07 PM (EST)

Yours is one possible interpretation. But this is definitely not what Smullyan had in mind, as I tried to explain in our previous correspondence.

The fellow has been born with a mental label of which he is aware. It's either this or that. When asked about his identification he simply reports the label.

Smullyan's formulation is clearly ambiguous. I am ready to admit that much. In fact I have. While coming up with other interpretations points to a certain agility of the mind, I am only interested in the one interpretation he has in mind. Otherwise, we shall be treading in circles with no end in sight.

You may be curious to have a look at the discussion on the Monty Hall Dilemma:

www.cut-the-knot.com/hall.shtml

There must be a list of links to other places on the Web. If not, just seaarch the Web. A small problem gave rise to an unending and heated discussion. I'd like to avoid its repetition.


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