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From: Mikko <mikko.levanto@iki.fi>
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 12:59:26 +0300
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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:

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.

-- 
Mikko