Re: How to write a self-referencial TM?

On 14/05/2025 22:40, Keith Thompson wrote:

Richard Heathfield <rjh@cpax.org.uk> writes:
[...]

Using a highly questionable collection of approximations about the
physical properties of 4mm mylar tape and the number of atoms in the
universe, I calculated that by devoting /everything/ to this tape we
could make it
>
5285412262156448202959830866807610993657505285
>
lightyears long (exACtly, of course).
>
It's still a long way off infinite, but I think it could possibly
qualify as 'long enough'.

 It's still not long enough for a TM that repeatedly advances its
position in one direction while indefinitely repeating the same state.

Indeed, but the existence of TMs for which it isn't long enough doesn't mean there aren't plenty of TMs for which a C90 would be more than adequate.
A hobbyist wishing to code up a TM shouldn't be put off by the fact that his laptop doesn't have an infinitely large hard disk.
<read and snipped>
--
Richard Heathfield
Email: rjh at cpax dot org dot uk
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