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From: Richard Damon <richard@damon-family.org>
Newsgroups: comp.theory,sci.logic
Subject: Re: Every D(D) simulated by H presents non-halting behavior to H ###
Date: Sun, 19 May 2024 13:17:30 -0400
Organization: i2pn2 (i2pn.org)
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On 5/19/24 10:03 AM, olcott wrote:
> 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?
>>
> 
> 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.
> 

Which has been proven incorrect.