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From: olcott <polcott333@gmail.com>
Newsgroups: comp.lang.c
Subject: Re: Can you see that D correctly simulated by H remains stuck in
 recursive simulation?
Date: Sat, 25 May 2024 06:42:59 -0500
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On 5/25/2024 4:59 AM, Mikko wrote:
> On 2024-05-24 16:57:36 +0000, olcott said:
> 
>> On 5/24/2024 10:01 AM, Fred. Zwarts wrote:
>>> Op 23.mei.2024 om 18:52 schreef olcott:
>>>> typedef int (*ptr)();  // ptr is pointer to int function in C
>>>> 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       }
>>>>
>>>> The above template refers to an infinite set of H/D pairs where D is
>>>> correctly simulated by pure function H. This was done because many
>>>> reviewers used the shell game ploy to endlessly switch which H/D was
>>>> being referred to.
>>>>
>>>> *Correct Simulation Defined*
>>>> This is provided because every reviewer had a different notion of
>>>> correct simulation that diverges from this notion.
>>>>
>>>> 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.
>>>>
>>>> *Execution Trace*
>>>> Line 11: main() invokes H(D,D); H(D,D) simulates lines 01, 02, and 
>>>> 03 of
>>>> D. This invokes H(D,D) again to repeat the process in endless recursive
>>>> simulation.
>>>
>>> The case can be simplified even more (D is not needed):
>>>
>>
>> We are ONLY asking about whether D correctly simulated by pure 
>> function H can possibly reach its own final state at line 06 and halt.
>>
>> Because H is a pure function we know that H halts.
> 
> We don't know that H halts. The OP said the opposite:
> 

The above references *pure function* H thus we do know
that the spec *requires* H to halt.
https://en.wikipedia.org/wiki/Pure_function


> On 2024-05-23 16:52:21 +0000, olcott said:
>> *Execution Trace*
>> Line 11: main() invokes H(D,D); H(D,D) simulates lines 01, 02, and 03 of
>> D. This invokes H(D,D) again to repeat the process in endless recursive
>> simulation.
> 
> To repeat in endless recursve simulation makes halting impossible.
> Apparently OP's interpretation of "pure function" does not imply
> halting.
> 

Every H is required to halt and return a value.
To make things simple every H returns the meaningless 56.
It is endless recursive simulation until H halts.

I had to refer to endless recursive simulation so that people
could get the gist of what is going on while hardly paying any
attention at all.

The reason that I had to add that H is a pure function is that
Richard tried to cheat using static local data. Prior to that
there was no requirement that H halt.

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