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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: Tue, 21 May 2024 08:54:09 -0500
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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?
> 

I initially read that as nonsense.
You are asking for the definition of correct simulation
that I have been providing for quite a while recently.

A c function is correctly simulated when its machine language
instructions are emulated with an x86 emulator in the order
that they are specified by the x86 machine language of this
c function.  For non-terminating functions we can only correctly
simulate N machine language instructions.

For the H/D pair we can simulate 1 to N instructions of D that
results in 0 to M recursive simulations of H simulating itself
simulating D.


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