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From: mmar@sphinx.UChicago.UUCP (Mitchell Marks)
Newsgroups: net.puzzle
Subject: Re: the \"yes-no mystery\" game
Message-ID: <1799@sphinx.UChicago.UUCP>
Date: Fri, 14-Mar-86 03:18:14 EST
Article-I.D.: sphinx.1799
Posted: Fri Mar 14 03:18:14 1986
Date-Received: Sun, 16-Mar-86 08:45:00 EST
References: <1619@decwrl.DEC.COM>
Reply-To: mmar@sphinx.UUCP (Mitchell Marks)
Organization: U Chicago
Lines: 65


I sent the mystery below to Pete Olpe, who originated this discussion.  Since
the topic seems to be catching interest on the net, I'll post it for general
consumption.  It's the most elaborate story of this type that I know.

As <1619decwrl.DEC.COM> (sorry, I've lost your name off screen) says, 
it's not obvious what procedure to use.  I'll answer questions either
by mail or in net.puzzle.  Considering the problems of turnaround
time, it's reasonable to allow several questions at one go.

The mystery:
   One day A (you could give them names, but they wouldn't matter) mails
a package to B; it contains an arm.  B receives it, opens it, glances
at the contents, wraps the package again, and mails it to C.  When C
gets it, he opens it, etc, and mails it on to D.  And so on, through
characters E, F, and G.  When G receives the package, opens it, looks
at the contents, he discards it.
   A couple of weeks later, E sees A walking down the street.  E gets
very angry, yells at A, and shoots him.  
   The mystery question: why does E shoot A?  A secondary question, which
you would probably have to answer along the way, is: why are they mailing
this arm around?

Q: Is it a human arm?
	A: Yes
Q: Is it a right arm?
	A: No
Q: Was B expecting the arm?
	A: Yes
Q: Were they _all_ expecting the arm?
	A: Yes, all those who received it were expecting an arm.
Q: What does that mean?  Why are you rephrasing my question?
	A: ...
Q: Do they live in the same city.
	A: Not all of them.
Q: But E and A live in the same city?
	A: Yes
Q: Do we care about their occupations?
	A: Two of them, yes.
Q: Have E and A met before the shooting incident?
	A: Oh yes.

Eventually you get to "How many arms does ___ have?" for each character,
or "Does ___ have two arms?", to keep to Y/N format.  Then you're well on
your way.

I think meta-questions are acceptable, and should get honest answers
(questions like "Does it matter whether ____?").  If the questioner
skips meta-questions, and asks something whose answer is not determined
in the underlying story-answer, the narrator is free to make up anything
plausible that's consistent with the story -- this isn't cheating, or
changing things post hoc.  If it's a really useful question and answer,
it may become part of the `official' story by the next time you hear
it.  (I suspect this is how the occupations of two of the characters
got accreted in as part of the arm story.)

It also seems reasonable to allow questions whose answer must come from
a small set, e.g. "How many fingers did the arm have?"  This avoids
the tedious transformation to "Did the arm have 5 fingers?" ... "Four?"
... "Three?" etc.  But beware presupposition-failure.
Do you want to pursue this, or just see the answer?
-- 

            -- Mitch Marks @ UChicago 
               ...ihnp4!gargoyle!sphinx!mmar