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From: thill@ssc-bee.UUCP (Tom Hill)
Newsgroups: net.puzzle
Subject: Who is the thief?
Message-ID: <304@ssc-bee.UUCP>
Date: Thu, 14-Mar-85 14:03:16 EST
Article-I.D.: ssc-bee.304
Posted: Thu Mar 14 14:03:16 1985
Date-Received: Sat, 16-Mar-85 02:27:52 EST
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Organization: Boeing Aerospace Co., Seattle, WA
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Get out your graph paper and try this one:

One of the six students A, B, C, D, E, F stole a book from the library
last Monday night.  Each student is questioned about whom they saw
at the library, and all tell the truth except the thief (it is possible
one student saw another without in turn being observed, but we assume
that one must have seen the other if both were there at the same time).
A saw B and E; B saw A and F; C saw D and F; D saw A and F; 
E saw B and C; and F saw C and E.  Who is the thief?


This is taken from APPLIED COMBINATORICS by Alan Tucker (page 215).
I highly recommend this text for anyone interested in combinatorics.


Have Fun,

Tom Hill