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Darren New schrieb:
> clipka wrote:
>> Note that I'm interpreting the grammatical construct "unbounded memory
>> tape" to read "unbounded thing called a memory tape", not "tape
>> constituting an unbounded [amount of] memory"; your interpretation may
>> differ.
>
> Given the mathematical definition of the memory tape in a TM, this
> interpretation makes no sense. Everyone says "unbounded tape" because
> that implies "unbounded amount of storage" given how the tape is
> defined. (I.e., it's defined as having one end as well as operations to
> move left and right.)
Erm... do you /really/ know what you're talking about?
Whenever a Turing machine's tape is defined as having /any/ end at all,
then it is defined as having /two/ ends, /both/ of which will be
automatically extended as needed.
But I prefer to stick to Turing's own description:
"...an infinite memory capacity obtained in the form of an /infinite
tape/..." (Turing 1948, p. 61)
There. Emphasis added. Any further questions?
(Yes, there /are/ variations on the theme that use a tape which is
bounded in /one/ direction only; these are, however, not classic generic
Turing machines.)
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