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From: "Fred. Zwarts" <F.Zwarts@HetNet.nl>
Newsgroups: comp.theory,sci.logic
Subject: Re: Can an abort decider be defined that cannot be fooled by any
 pathological input?
Date: Tue, 26 Mar 2024 09:59:31 +0100
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Op 25.mrt.2024 om 18:33 schreef olcott:
> On 3/25/2024 11:16 AM, Fred. Zwarts wrote:
>> Op 25.mrt.2024 om 17:04 schreef olcott:
>>> On 3/25/2024 10:48 AM, Fred. Zwarts wrote:
>>>> Op 25.mrt.2024 om 16:17 schreef olcott:
>>>>> On 3/24/2024 3:51 AM, Fred. Zwarts wrote:
>>>>>> Op 24.mrt.2024 om 05:55 schreef olcott:
>>>>>>> Can an abort decider be defined that cannot be fooled by any 
>>>>>>> pathological input?
>>>>>>>
>>>>>>> 01 int D(ptr x)  // ptr is pointer to int function
>>>>>>> 02 {
>>>>>>> 03   int Halt_Status = H(x, x);
>>>>>>> 04   if (Halt_Status)
>>>>>>> 05     HERE: goto HERE;
>>>>>>> 06   return Halt_Status;
>>>>>>> 07 }
>>>>>>> 08
>>>>>>> 09 void main()
>>>>>>> 10 {
>>>>>>> 11   H(D,D);
>>>>>>> 12 }
>>>>>>>
>>>>>>> Of all of the elements of the set of H(D,D) where H simulates its
>>>>>>> input there are matched pairs of otherwise identical elements that
>>>>>>> only differ by whether they abort their simulation or not.
>>>>>>>
>>>>>>> The half of these that don't abort are incorrect because all 
>>>>>>> deciders
>>>>>>> must halt. This makes the other half correct about the abort/no 
>>>>>>> abort
>>>>>>> decision.
>>>>>>
>>>>>> No. The other, aborting, half is just wrong, because it aborts 
>>>>>> when it is not needed. So, the half that aborts is wrong and it 
>>>>>> may be argued that it is better to not abort something that halts 
>>>>>> on its own and that 
>>>>>
>>>>> At least two software engineers with masters degrees in computer 
>>>>> science
>>>>> disagree.
>>>>
>>>> Two is not many, considering that with Google for any invalid idea 
>>>> it is easy to find a several people with a master degree supporting it.
>>>>
>>>>> Exactly what are you software engineering skills?
>>>>
>>>> I have been professionally programming since 1986 in several 
>>>> languages. (Non professionally I started programming in 1975). Since 
>>>> about 1990 I programmed in C and since about 2000 in C++.
>>>>
>>>>
>>>>> I have been a professional C++ software engineer since Y2K.
>>>>
>>>> I'm sorry to hear that olcott has been so smart, but now he does not 
>>>> even sees what even a beginner sees.
>>>
>>> Can D correctly simulated by H terminate normally?
>>> 01 int D(ptr x)  // ptr is pointer to int function
>>> 02 {
>>> 03   int Halt_Status = H(x, x);
>>> 04   if (Halt_Status)
>>> 05     HERE: goto HERE;
>>> 06   return Halt_Status;
>>> 07 }
>>> 08
>>> 09 void main()
>>> 10 {
>>> 11   H(D,D);
>>> 12 }
>>>
>>> *Execution Trace*
>>> Line 11: main() invokes H(D,D);
>>>
>>> *keeps repeating* (unless aborted)
>>> Line 03: simulated D(D) invokes simulated H(D,D) that simulates D(D)
>>
>> Even a beginner sees that, if the H that aborts is chosen, simulated 
>> H(D,D) aborts and returns false (unless aborted). So simulated D halts 
>> (unless aborted).
>>
> 
> I am estimating that you must be fibbing about your programming skill.
> The D simulated by any implementation of H (that aborts or does not
> abort its simulation) shown above cannot possibly reach its own line 04
> also shown above.

Even beginners see that for the H we are talking about, that aborts and 
returns false, the only reason that D does not reach line 04 is that it 
is aborted. So, the abortion was premature and incorrect. The correct 
simulation of D halts (unless aborted).