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From: Richard Heathfield <rjh@cpax.org.uk>
Newsgroups: comp.lang.c
Subject: Re: Proving the: Simulating termination analyzer Principle
Date: Sun, 6 Apr 2025 01:59:39 +0100
Organization: Fix this later
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On 06/04/2025 01:35, olcott wrote:
> On 4/5/2025 5:31 PM, Richard Heathfield wrote:
>> On 05/04/2025 23:20, olcott wrote:
>>> On 4/5/2025 4:58 PM, Richard Heathfield wrote:
>>
>> <snip>
>>
>>>> hp(arg candidate, arg testdata)
>>>> {
>>>>    if(terminates(candidate(testdata)))
>>>>    {
>>>>      while(forever);
>>>>    }
>>>>    else
>>>>    {
>>>>      halt;
>>>>    }
>>>> }
>>>>
>>>> We then invoke the program:
>>>>
>>>> hp(hp, hp)
>>>>
>>>> and try to predict what terminates() will report, and of 
>>>> course the answer is that we don't know, because neither does 
>>>> terminates(). The function cannot be written.
>>>>
>>>
>>> Understanding my simpler example was a mandatory
>>> prerequisite
>>
>> No, it wasn't.
>>
>> Understanding my example isn't mandatory either, which is just 
>> as well where you're concerned.
>>
>>> int DD()
>>> {
>>>    int Halt_Status = HHH(DD);
>>>    if (Halt_Status)
>>>      HERE: goto HERE;
>>>    return Halt_Status;
>>> }
>>
>> That's fine, but it does beg the HHH() question. You are 
>> handwaving it for the same reason I am, which is that it can't 
>> be written. The difference between us is that I know it and you 
>> don't.
>>
> 
> HHH(DDD) is isomorphic to HHH(DD),

Irrelevant.

> yet failing
> to understand that HHH(DDD) meets the
> *Simulating termination analyzer Principle*
> prevents the significance of this from being seen.

It has no significance.

There are only two possibilities: either it always gives the 
right answer or it doesn't. If it gives the wrong answer, it's of 
no interest.

If it is claimed always to give the right answer, it becomes 
possible (as shown above in the chevrons) to write a program for 
which it will not be able to work out the right answer - reductio 
ad absurdum.

Your 'principle' doesn't matter a jot.

-- 
Richard Heathfield
Email: rjh at cpax dot org dot uk
"Usenet is a strange place" - dmr 29 July 1999
Sig line 4 vacant - apply within