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From: jtwigge@partridge.attiaa.attistel.co.uk (Jon Twigge)
Subject: Re: Thought Question
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Date: Wed, 15 Feb 1995 17:43:45 GMT
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In article <3hsv53$ipj@oznet03.ozemail.com.au>, Alan Tonisson
<tonisson@ozemail.com.au> wrote:

> By the way, I can give an example of a finite system that completely
models itself in
> some sense without being infinite:
> 
> Way back when I was studying at university, a computer science lecturer
challenged us
> with the problem of either writing a computer program which prints its
own source or
> proving that it could not be done.  I convinced myself that it was
impossible because
> it must require some sort of infinite recursion, but couldn't prove it,
but a friend
> of mine won the challenge and wrote a Pascal program which prints it's
own source.
> A few years later when I was bored I figured out how to do it and wrote
one in C.
> It does not use any data external to itself and, if I remember
correctly, it only
> uses putc.  I can probably dig it up if it is of interest to anyone.
> 
> I figure that such a program models itself in some sense.
> 
> Alan Tonisson (tonisson@ozemail.com.au)
> Rune Research Pty Ltd

I dont think these programs model themselves, except superficially.  To do
that they would need to be able to reproduce the environment which they
need to run in as well.  This is like saying a person capable of building
a model of themselves would not be creating life. Whether there is a point
at which the detail of such a model would be such that it was alive is i
believe a religious question. Is a program capable of wondering whether a
copy of itself would be a new program or not?

 JonT
