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From: verma@ucla-cs.UUCP
Newsgroups: net.puzzle
Subject: Re: puzzle  (same old liar puzzle)    (* spoiler? *)
Message-ID: <8936@ucla-cs.ARPA>
Date: Thu, 13-Feb-86 10:42:35 EST
Article-I.D.: ucla-cs.8936
Posted: Thu Feb 13 10:42:35 1986
Date-Received: Sat, 15-Feb-86 06:22:55 EST
References: <1644@hound.UUCP>
Reply-To: verma@ucla-cs.UUCP (Thomas S. Verma )
Organization: UCLA Computer Science Department
Lines: 43

In article <1644@hound.UUCP> 5125kaf@hound.UUCP (K.FRIEDMAN) writes:
>
>always lies. You can ask either person one question and only
>one question in order to determine which way the hospital is.
>What would be the question and to whom would you ask it?
                                ^^^^^^^
>How would this question help you to determine which way to go?
     
        If I get to choose, then I will ask the truth teller which
        way to go.  But if I dont know which one he is, then I would
        ask either one the question (pointing to either road):

                Is the truth value of the statement: 'That is the
                way to the hospital' the same as the truth value
                to the statement 'You never lie' ?
     
        If he says yes then the road I am pointing to must be the road
        to the hospital.

        There are four cases:
     
        1) It IS the road, and he never lies
                the two statements are both thue, thus since
                he never lies, he will say YES

        2) It IS the road, but he always lies
                the two statements do not have the same truth value,
                thus the answer is no, but he always lies, so he
                says YES

        3) It IS NOT the road, and he never lies
                again the two are not the same, but he is the
                truth teller, thus he must say NO

        4) It IS NOT the road, and he always lies
                the two statements are both false, but since he
                always lies he must say NO
     
                                        No flame intended, but
                                        hasen't everyone seen
                                        this puzzle in 2nd grade?

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