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From: olcott <polcott333@gmail.com>
Newsgroups: comp.theory
Subject: Re: Every D(D) simulated by H presents non-halting behavior to H ###
Date: Mon, 20 May 2024 12:56:54 -0500
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On 5/20/2024 3:21 AM, Mikko wrote:
> On 2024-05-19 14:03:01 +0000, olcott said:
> 
>> On 5/19/2024 8:48 AM, Mikko wrote:
>>> On 2024-05-19 12:34:08 +0000, olcott said:
>>>
>>>> On 5/19/2024 2:53 AM, Mikko wrote:
>>>>> On 2024-05-18 15:34:36 +0000, James Kuyper said:
>>>>>
>>>>>> On 5/18/24 09:02, Mikko wrote:
>>>>>>> On 2024-05-17 17:14:01 +0000, olcott said:
>>>>>>
>>>>>> I recommend ignoring olcott - nothing good ever comes from paying
>>>>>> attention to him.
>>>>>>
>>>>>>>> On 5/17/2024 5:53 AM, Mikko wrote:
>>>>>>>>> On 2024-05-16 14:50:19 +0000, olcott said:
>>>>>>>>>
>>>>>>>>>> On 5/16/2024 5:48 AM, Mikko wrote:
>>>>>>>>>>> On 2024-05-15 15:24:57 +0000, olcott said:
>>>>>> ...
>>>>>>>>>>>> typedef int (*ptr)();  // ptr is pointer to int function
>>>>>>>>>>>> 00 int H(ptr x, ptr x);
>>>>>>>>>>>> 01 int D(ptr x)
>>>>>>>>>>>> 02 {
>>>>>>>>>>>> 03   int Halt_Status = H(x, x);
>>>>>>>>>>>> 04   if (Halt_Status)
>>>>>>>>>>>> 05     HERE: goto HERE;
>>>>>>>>>>>> 06   return Halt_Status;
>>>>>>>>>>>> 07 }
>>>>>>>>>>>> 08
>>>>>>>>>>>> 09 int main()
>>>>>>>>>>>> 10 {
>>>>>>>>>>>> 11   H(D,D);
>>>>>>>>>>>> 12   return 0;
>>>>>>>>>>>> 13 }
>>>>>>>>>>>
>>>>>>>>>>> Can you find any compiler that is liberal enough to accept that?
>>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> It has been fully operational code under Windows and
>>>>>>>>>> Linux for two years.
>>>>>>>>>
>>>>>>>>> If your compiler does not reject that program it is not a 
>>>>>>>>> conforming
>>>>>>>>> C compiler. The semantics according to C standard is that a 
>>>>>>>>> diagnostic
>>>>>>>>> message must be given. The standard does not specify what 
>>>>>>>>> happens if
>>>>>>>>> you execute that program anyway.
>>>>>>>>>
>>>>>>>>
>>>>>>>> It is not nit picky syntax that is the issue here.
>>>>>>>> The SEMANTICS OF THE C PROGRAMMING LANGUAGE SPECIFIES
>>>>>>>>
>>>>>>>> No D simulated correctly by any H of every H/D pair specified
>>>>>>>> by the above template ever reaches its own line 06 and halts.
>>>>>>>
>>>>>>> The standard allows that an program is executed but does not
>>>>>>> specify what happens when an invalid program is executed.
>>>>>>
>>>>>> You've cross-posted this to comp.lang.c after a long-running 
>>>>>> discussion
>>>>>> solely on comp.theory. Presumably you're doing that because you want
>>>>>> some discussion about what the standard says about this code. For the
>>>>>> sake of those of us who have not been following that discussion on
>>>>>> comp.theory, could you please identify what it is that you think 
>>>>>> renders
>>>>>> this code invalid? Offhand, I don't see anything wrong with it, 
>>>>>> but I'm
>>>>>> far more reliable when I say "I see an error" than when I say "I 
>>>>>> don't
>>>>>> see an error".
>>>>>>
>>>>>>
>>>>>>>> Fully operational software that runs under Widows and Linux
>>>>>>>> proves that the above is true EMPIRICALLY.
>>>>>>>
>>>>>>> No, it does not. As the program is not strictly comforming
>>>>>>> and uses a non-standard extension some implementation may
>>>>>>> execute it differently or refuse to execute.
>>>>>>
>>>>>> Which non-standard extension does it use?
>>>>>
>>>>> The main question is whether both arguments of H on the line 00 can 
>>>>> have
>>>>> the same name.
>>>>
>>>> That was a typo that I did not believe when told because so may people
>>>> continue to lie about the behavior of D correctly simulated by H.
>>>
>>> How does the D that is correctly simulated by H different from any
>>> D that is incorrectly simulated by H nor not simulated by H?
> 
> Oops, I made a typo on the last line. Pro "nor" lege "or".
> Fortunately most of the typos are harmless but this one
> might be a problem.
> 
>> typedef int (*ptr)();  // ptr is pointer to int function
>> 00 int H(ptr p, ptr i);
>> 01 int D(ptr p)
>> 02 {
>> 03   int Halt_Status = H(p, p);
>> 04   if (Halt_Status)
>> 05     HERE: goto HERE;
>> 06   return Halt_Status;
>> 07 }
>> 08
>> 09 int main()
>> 10 {
>> 11   H(D,D);
>> 12   return 0;
>> 13 }
>>
>> In the above case a simulator is an x86 emulator that correctly
>> emulates at least one of the x86 instructions of D in the order
>> specified by the x86 instructions of D.
>>
>> This may include correctly emulating the x86 instructions of H
>> in the order specified by the x86 instructions of H thus calling
>> H(D,D) in recursive simulation.
> 
> As far as I can see, that does not say anything that was not already
> said (but there is a minor presentational imporvement) and in particular
> does not answer my question.
> 

For two or three years everyone has been claiming that the
above measures of correct simulation are incorrect. Their
"ultimate" measure of a "correct" simulation is that D does
whatever they expect D to do.

-- 
Copyright 2024 Olcott "Talent hits a target no one else can hit; Genius
hits a target no one else can see." Arthur Schopenhauer