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From: Mikko <mikko.levanto@iki.fi>
Newsgroups: comp.lang.c
Subject: Re: D correctly simulated by pure function H cannot possibly reach its, own line 06
Date: Mon, 27 May 2024 11:47:05 +0300
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On 2024-05-26 16:54:51 +0000, olcott said:

> On 5/26/2024 11:04 AM, Mikko wrote:
>> On 2024-05-26 13:12:08 +0000, olcott said:
>>> I had to make the subject line of the thread a little less accurate
>>> so that people could get the gist of what I was saying. Now I have
>>> made it precise.
>> 
>> Subject lines typically are as they are limited to one line. That's
>> not a problem.
>> 
> 
> *I finally have much better words*
> 
> 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       }
> 
> When we see that D correctly simulated by pure simulator H would remain
> stuck in recursive simulation then we also know that D never reaches its
> own line 06 and halts in less than an infinite number of correctly
> simulated steps.
> 
> This means that D correctly simulated by pure function H also never
> reaches it own line 06 and halts.

Nothing C specific there. Other aspects are discussed in comp.theory.

-- 
Mikko