Path: news.eternal-september.org!eternal-september.org!.POSTED!not-for-mail
From: Richard Heathfield <rjh@cpax.org.uk>
Newsgroups: comp.theory
Subject: Re: Overcoming the proof of undecidability of the Halting Problem by
 a simple example in C
Date: Mon, 19 May 2025 04:16:30 +0100
Organization: Fix this later
Lines: 66
Message-ID: <100e7qg$1e5fs$1@dont-email.me>
References: <1005jsk$3akrk$1@dont-email.me>
 <bc6f0f045212bdfb7f7d883426873a09e37789ea@i2pn2.org>
 <1005u6v$3cpt2$1@dont-email.me> <1005v0p$3b07v$1@dont-email.me>
 <10063u0$3dmiv$1@dont-email.me> <1006on8$3l9t7$1@dont-email.me>
 <1007kgq$3qb7l$9@dont-email.me> <1009lm9$b15q$1@dont-email.me>
 <100ceum$uvq0$1@dont-email.me> <87ecwl1s2p.fsf@bsb.me.uk>
 <100dscu$18b5s$1@dont-email.me> <87v7pxzbp4.fsf@bsb.me.uk>
 <100du9m$18m8u$1@dont-email.me> <100dvuj$18b5q$2@dont-email.me>
 <100e17m$194d7$1@dont-email.me> <100e3qo$1d7a1$1@dont-email.me>
 <100e5g1$1do0r$1@dont-email.me>
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Injection-Date: Mon, 19 May 2025 05:16:32 +0200 (CEST)
Injection-Info: dont-email.me; posting-host="be58ce700b7a791d98bdef6cb205f490";
	logging-data="1512956"; mail-complaints-to="abuse@eternal-september.org";	posting-account="U2FsdGVkX1+kglLQiqTauspvS0eE/I+ZJ8FtsqVQiAtMECCndVKiBQ=="
User-Agent: Mozilla Thunderbird
Cancel-Lock: sha1:oIkze4vs2SGJO8OWsYG3RvVS2NY=
In-Reply-To: <100e5g1$1do0r$1@dont-email.me>
Content-Language: en-GB

On 19/05/2025 03:36, olcott wrote:
> On 5/18/2025 9:08 PM, Richard Heathfield wrote:
>> On 19/05/2025 02:24, olcott wrote:
>>> It was stipulated that HHH does simulate DDD.
>>
>> That's all right then.
>>
>> It's stipulated that you are correct.
>>
> 
> Unless is it known that one C function
> cannot possibly simulate another the
> stipulation must be accepted by anyone
> wanting an honest dialogue.
  There is a way it could be done within the rules of C, but the 
way that you do it is not that way.

We know that programs exist that can translate C source code. The 
obvious examples are compilers and interpreters. (Your HHH is 
neither, because you don't actually give it C source to lex.)

We can therefore envisage the possibility of encapsulating an 
interpreter's capability within a C function, and handing it a C 
function to be interpreted - something like eval(char 
*c_function_source), where c_function_source points to the first 
byte of the source code of the function definition you wish to 
simulate, given as C source in a \n-separated and null-terminated 
array of printable, readable characters.

eval() would lex the C (break it into individual tokens), parse 
it, construct an abstract syntax tree, and finally walk the tree 
interpreting the code as it went.

It would be a lot more complicated than that in practice, but 
that's the gist of how you'd do it within the rules of C.

All this is true, so we may reasonably deduce that it is at least 
in theory possible for a C function to simulate another, but in 
no way does that imply either that HHH is a C function (indeed, 
over a third of it consists of assembly language directives) nor 
that it correctly simulates anything. The stipulation that HHH 
correctly simulates C has not been shown to be true, and is very 
likely to be false. Trying to trick honest people into accepting 
a false stipulation by attempting to smear a refusal as 
'dishonest' is a mere shyster trick.

You can stipulate whatever you like, and use that stipulation to 
make deductions. You could stipulate that a tail is a leg and 
deduce that a horse has five legs. The logic would be impeccable, 
but it's still nonsense, and a horse still only has four legs, 
because stipulating that a tail is a leg doesn't make it a leg.

You can stipulate that HHH correctly simulates DDD, but that 
doesn't mean that HHH correctly simulates DDD; it only means that 
you have stipulated that it does.

You can stipulate that you're right, of course, and as far as 
you're concerned that would be the end of the argument because 
anyone who disagrees with you is stipulated to be wrong.

-- 
Richard Heathfield
Email: rjh at cpax dot org dot uk
"Usenet is a strange place" - dmr 29 July 1999
Sig line 4 vacant - apply within