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From: immibis <news@immibis.com>
Newsgroups: comp.theory
Subject: Re: D correctly simulated by H cannot possibly reach its own line 06
 and halt
Date: Fri, 31 May 2024 10:39:44 +0200
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On 31/05/24 00:01, olcott wrote:
> On 5/30/2024 4:54 PM, joes wrote:
>> Am Thu, 30 May 2024 09:55:24 -0500 schrieb 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 left hand-side are line numbers of correct C code.
>>> This code does compile and does conform to c17.
>>>
>>> Everyone with sufficient knowledge of C can easily determine that D
>>> correctly emulated by any *pure function* H (using an x86 emulator)
>>> cannot possibly reach its own simulated final state at line 06 and halt.
>> Yeah, of course not, if H doesn’t halt.
>>
> 
> To actually understand my words (as in an actual honest dialogue)
> you must pay careful attention to every single word. Maybe you
> had no idea that *pure functions* must always halt.

H doesn't halt. If you are right, H isn't a pure function.