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From: sylvere@unige.ch (Silvere Martin-Michiellot)
Subject: Re: Thought Question
Message-ID: <1995Feb16.130729.7664@news.unige.ch>
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Reply-To: sylvere@unige.ch
Organization: University of Geneva, Switzerland
References: <3hsv53$ipj@oznet03.ozemail.com.au>
Date: Thu, 16 Feb 1995 13:07:29 GMT
Lines: 36

In article ipj@oznet03.ozemail.com.au, Alan Tonisson <tonisson@ozemail.com.au> writes:
>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.

Don't think so (but send me your C source),

In fact, when you write such a program, you use a counter that prints something,
then increments, then prints the next instruction.... The problem is to chose if you
write down that counter or just the source code. If you want to write down that
counter then YOU WILL NEVER BE ABLE TO WRITE ALL ITS STATES.
A typical example is the case you want to save on disk a perfect image of all your RAM.
It can only be CORRECTELY down by using another computer that monitors the activity.
Otherwise, you fall into the counter trap.

The general problem is far more complex and interesting (philosophic aspect), but I
will tell more only if you have questions you want to ask me.

-----------------

"Is anyone alive down there ?"
  

Silvere MARTIN-MICHIELLOT


