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From: Mikko <mikko.levanto@iki.fi>
Newsgroups: comp.theory
Subject: Re: Simulating termination analyzers by dummies --- What does halting mean?
Date: Thu, 20 Jun 2024 08:29:14 +0300
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On 2024-06-19 14:05:29 +0000, olcott said:

> On 6/19/2024 4:29 AM, Alan Mackenzie wrote:
>> olcott <polcott333@gmail.com> wrote:
>>> On 6/18/2024 4:36 PM, Alan Mackenzie wrote:
>>>> [ Followup-To: set ]
>> 
>>>> In comp.theory olcott <polcott333@gmail.com> wrote:
>>>>> On 6/18/2024 12:57 PM, joes wrote:
>>>>>> Am Tue, 18 Jun 2024 12:25:44 -0500 schrieb olcott:
>>>>>>> On 6/18/2024 12:06 PM, joes wrote:
>>>>>>> void DDD()
>>>>>>> {
>>>>>>> H0(DDD);
>>>>>>> }
>>>>>>> DDD correctly simulated by any H0 cannot possibly halt.
>>>>>>>> DDD halts iff H0 halts.
>> 
>>>>>> So H0 returns "doesn't halt" to DDD, which then stops running,
>>>>>> so H0 should have returned "halts".
>> 
>>>>> This was three messages ago.
>>>>> I had to make sure that you understood that halting
>>>>> does not mean stopping for any reason and only includes
>>>>> the equivalent of terminating normally.
>> 
>>>> No.  You're wrong, here.  A turing machine is either running or it's
>>>> halted.  There's no third alternative.  If your C programs are not in one
>>>> of these two states, they're not equivalent to turing machines.
>> 
>>> Although I agree with this there seems to be nuances of
>>> disagreement across the experts.
>> 
>> I doubt that very much.  The whole point of turing machines is to remove
>> ambiguity and unneeded features from the theory of computation.  A third
>> alternative state is unneeded.
>> 
> 
> Some people say that a TM can halt in a non-final state.

People may use different words to express the same facts. What some
people call "halting in a non-final state" is called "rejecting" by
some other people. But the facts are what they are independently of
the words used to express them.

-- 
Mikko