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Article <20240723231718.796@kylheku.com>
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From: Kaz Kylheku <643-408-1753@kylheku.com>
Newsgroups: comp.lang.lisp,comp.lang.scheme
Subject: Re: Non-determinism
Date: Wed, 24 Jul 2024 08:18:24 -0000 (UTC)
Organization: A noiseless patient Spider
Lines: 44
Message-ID: <20240723231718.796@kylheku.com>
References: <v7pboq$1d67r$1@dont-email.me> <v7peea$1djes$1@dont-email.me>
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On 2024-07-24, B. Pym <Nobody447095@here-nor-there.org> wrote:
> B. Pym wrote:
>
>> Problem 4.42 in SICP
>> 
>> Five school girls took an exam. As they think thattheir
>> parents are too much interested in their score, they promise
>> that they write one correct and one wrong informations to
>> their parents. Followings are parts of their letters
>> concerning their result:
>> 
>> Betty: 	Kitty was the second and I third.
>> Ethel: 	I won the top and Joan the second.
>> Joan: 	I was the third and poor Ethel the last.
>> Kitty: 	I was the second and Mary the fourth.
>> Mary: 	I was the fourth. Betty won the top.
>> 
>> Guess the real order of the five school girls. 
>
> Shorter:

[ snip astonishing 130 line continuation-driven spaghetti behemoth ]

> ((kitty joan betty mary ethel))

$ txr girls.tl
#(kitty joan betty mary ethel)

$ cat girls.tl
(defun one-truth (g i1 n1 i2 n2)
  (neq (eq [g i1] n1) (eq [g i2] n2)))

(each ((g (perm #(kitty ethel joan mary betty) 5)))
  (when (and (one-truth g 1 'kitty 2 'betty)
             (one-truth g 0 'ethel 1 'joan)
             (one-truth g 2 'joan 4 'ethel)
             (one-truth g 1 'kitty 3 'mary)
             (one-truth g 3 'mary 0 'betty))
    (prinl g)))

-- 
TXR Programming Language: http://nongnu.org/txr
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