Path: news.eternal-september.org!eternal-september.org!.POSTED!not-for-mail
From: "Fred. Zwarts" <F.Zwarts@HetNet.nl>
Newsgroups: comp.theory
Subject: Re: Incorrect requirements --- Computing the mapping from the input
 to HHH(DD)
Date: Sat, 10 May 2025 10:05:32 +0200
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Op 09.mei.2025 om 17:48 schreef olcott:
> On 5/9/2025 3:47 AM, Fred. Zwarts wrote:
>> Op 09.mei.2025 om 04:23 schreef Keith Thompson:
>>> Richard Damon <richard@damon-family.org> writes:
>>>> On 5/8/25 7:53 PM, olcott wrote:
>>> [...]
>>>>> void DDD()
>>>>> {
>>>>>     HHH(DDD);
>>>>>     return;
>>>>> }
>>>>> We don't need to look at any of my code for me
>>>>> to totally prove my point. For example when
>>>>> the above DDD is correctly simulated by HHH
>>>>> this simulated DDD cannot possibly reach its own
>>>>> "return" instruction.
>>>>
>>>> And thus not correctly simulatd.
>>>>
>>>> Sorry, there is no "OS Exemption" to correct simulaiton;.
>>>
>>> Perhaps I've missed something.  I don't see anything in the above that
>>> implies that HHH does not correctly simulate DDD.  Richard, you've read
>>> far more of olcott's posts than I have, so perhaps you can clarify.
>>>
>>> If we assume that HHH correctly simulates DDD, then the above code is
>>> equivalent to:
>>>
>>>      void DDD()
>>>      {
>>>        DDD();
>>>        return;
>>>      }
>>>
>>> which is a trivial case of infinite recursion.  As far as I can tell,
>>> assuming that DDD() is actually called at some point, neither the
>>> outer execution of DDD nor the nested (simulated) execution of DDD
>>> can reach the return statement.  Infinite recursion might either
>>> cause a stack overflow and a probable program crash, or an unending
>>> loop if the compiler implements tail call optimization.
>>>
>>> I see no contradiction, just an uninteresting case of infinite
>>> recursion, something that's well understood by anyone with a
>>> reasonable level of programming experience.  (And it has nothing to
>>> do with the halting problem as far as I can tell, though of course
>>> olcott has discussed the halting problem elsewhere.)
>>>
>>> Richard, what am I missing?
>>>
>>
>> What you are missing is that the next step of olcott is to say that 
>> when he uses the 'exact same HHH, with only some extra code to abort 
>> the simulation', it is still an infinite recursion. He does not 
>> understand that adding the abort code makes the behaviour 
>> fundamentally different. 
> 
> When 1 or more statements of DDD are correctly simulated
> by HHH this correctly simulated DDD cannot possibly reach
> its own "return statement" final halt state.
> 
You see? Exactly what I predicted. Now he uses another HHH that does not 
correctly simulate the whole input, but only makes a start. He will 
still hold his claim that there is an infinite recursion and may quote a 
C expert, Keith Thompson, to support his claim. The only way out is that 
Keith Thompson explicitly explains that his example only holds for the 
simulator that does not stop after 1 or more statements.