X-Message-Number: 9288
Subject: And you thought this wasn't a humor list....
Date: Sun, 15 Mar 1998 22:25:44 -0500
From: "Perry E. Metzger" <>

> From: Ettinger <>
> Subject: Church-Turing etc
[...]
> Donaldson's recent #9272 includes a reminder that Turing machines
> are SEQUENTIAL, hence not well suited for recursive functions, for
> which parallel processors are much better

Not only do you misrepresent Mr. Donaldson's position (which I
disagree with but which is at least not ridiculous), but you display a
certain, shall we say, utter ignorance of the topic you are
discussing.

For the record:

0) The term "recursive function" is rather meaningless in this
context. You probably would mean "recursive algorithm" if you knew
anything about computers.

1) Thomas Donaldson noted that recursive algorithms *don't* look much
like the real world's processes and contended (inaccurately) that
Turing Machines mostly execute those. (In fact, although recursive
algorithms can always be translated into iterative ones and vice
versa, Turing Machines tend to use iterative algorithms, to the extent 
that anyone ever writes programs for actual Turing Machines. (In
general, no one actually writes programs for real Turing Machines --
they are useful mostly as a mathematical construct.))

2) Sequential machines and parallel machines both execute recursive
algorithms with equal ease. Maybe you'd better learn what a recursive
algorithm is *first*.

3) There is also a concept being bandied about here, the "Recursively
Enumerable Languages". I suggest reading a book on automata theory
before attempting to post any messages using that term, unless, of
course, you want to provide your readers with more amusement.

> This helps to focus attention on the MEANING of the Church-Turing
> thesis. IN WHAT SENSE can a Turing machine emulate any computer?
> Only in the sense that it can, in principle, eventually arrive at
> the same results, or print out the same answers.

Boy, Mr. Ettinger, you've really managed a coup of logic
there. Perhaps tomorrow you'd like to paraphrase mathematical
principle for us.

> Does a moving tape have feeling?

Does a neuron have feelings?


Perry

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