Path: news.eternal-september.org!eternal-september.org!.POSTED!not-for-mail
From: Ben Bacarisse <ben@bsb.me.uk>
Newsgroups: comp.theory
Subject: Re: Analysis of =?utf-8?Q?Flibble=E2=80=99s?= Latest: Detecting vs.
 Simulating Infinite Recursion ZFC
Date: Fri, 23 May 2025 14:00:35 +0100
Organization: A noiseless patient Spider
Lines: 71
Message-ID: <87a573xz0s.fsf@bsb.me.uk>
References: <Ms4XP.801347$BFJ.668081@fx13.ams4>
	<100jpv9$2m0ln$4@dont-email.me> <100kt0c$2tae8$3@dont-email.me>
	<100ktr7$2reaa$1@dont-email.me> <100l09v$2tae8$5@dont-email.me>
	<100l1ov$2ul3j$1@dont-email.me> <100l3jh$2v0e9$1@dont-email.me>
	<100l5c8$2ul3j$2@dont-email.me> <100l75g$2vpq3$1@dont-email.me>
	<100l887$2ul3i$2@dont-email.me> <100l9gh$30aak$1@dont-email.me>
	<100lc4o$30pgm$1@dont-email.me> <100ld1u$312c9$1@dont-email.me>
	<100lg4g$31jt3$1@dont-email.me> <100lkdv$32ib3$1@dont-email.me>
	<100lmif$32v06$1@dont-email.me> <100lmp3$32ven$1@dont-email.me>
	<100m319$38k55$2@dont-email.me>
	<87jz69xlpx.fsf@nosuchdomain.example.com>
	<100mder$39slu$2@dont-email.me> <100oipb$3oge1$1@dont-email.me>
MIME-Version: 1.0
Content-Type: text/plain
Injection-Date: Fri, 23 May 2025 15:00:35 +0200 (CEST)
Injection-Info: dont-email.me; posting-host="5f842c4fba7e64780966dc59bd931b69";
	logging-data="105056"; mail-complaints-to="abuse@eternal-september.org";	posting-account="U2FsdGVkX1/D4gNvLGa9/hwbS5RntgDTDxIB7V+BppM="
User-Agent: Gnus/5.13 (Gnus v5.13)
Cancel-Lock: sha1:aDOPbQnDLlBe+AmNVKYdA2EFJNk=
	sha1:8VMkvSasXO/bhqLt5N1dI93gcRw=
X-BSB-Auth: 1.ffd0476de149a4b266ea.20250523140035BST.87a573xz0s.fsf@bsb.me.uk

Mike Terry <news.dead.person.stones@darjeeling.plus.com> writes:

> On 22/05/2025 06:41, Richard Heathfield wrote:
>> On 22/05/2025 06:23, Keith Thompson wrote:
>>> Richard Heathfield <rjh@cpax.org.uk> writes:
>>>> On 22/05/2025 00:14, olcott wrote:
>>>>> On 5/21/2025 6:11 PM, Richard Heathfield wrote:
>>> [...]
>>>>>> Turing proved that what you're asking is impossible.
>>>>>>
>>>>> That is not what he proved.
>>>>
>>>> Then you'll be able to write a universal termination analyser that can
>>>> correctly report for any program and any input whether it halts. Good
>>>> luck with that.
>>>
>>> Not necessarily.
>> Of course not. But I'm just reflecting. He seemed to think that my
>> inability to write the kind of program Turing envisaged (an inability
>> that I readily concede) is evidence for his argument. Well, what's sauce
>> for the goose is sauce for the gander.
>> 
>>> Even if olcott had refuted the proofs of the
>>> insolvability of the Halting Problem -- or even if he had proved
>>> that a universal halt decider is possible
>> And we both know what we both think of that idea.
>> 
>>> -- that doesn't imply
>>> that he or anyone else would be able to write one.
>> Indeed.
>> 
>>> I've never been entirely clear on what olcott is claiming.
>> Nor I. Mike Terry seems to have a pretty good handle on it, but no matter
>> how clearly he explains it to me my eyes glaze over and I start to snore.
>
> Hey, it's the way I tell 'em!
>
> Here's what the tabloids might have said about it, if it had made the
> front pages when the story broke:
>
>   COMPUTER BOFFIN IS TURING IN HIS GRAVE!
>
>   An Internet crank claims to have refuted Linz HP proof by creating a
>   Halt Decider that CORRECTLY decides its own "impossible input"!
>   The computing world is underwhelmed.
>
> Better?  (Appologies for the headline, it's the best I could come up
> with.)

And the big picture is that this can be done because false is the
correct halting decision for some halting computations.  He has said
this explicitly (as I have posted before) but he has also explained it
in words:

| When-so-ever a halt decider correctly determines that its input would
| never halt unless forced to halt by this halt decider this halt
| decider has made a correct not-halting determination.

Or perhaps you prefer this explanation from 2023:

| (1) A return value of 1 from H(D,D) means the input to H(D,D) has halted
|
| (2) A return value of 0 from H(D,D) has been redefined to mean
|     (a) D does not halt
|     (b) D has been defined to do the opposite of whatever Boolean value
|         that H returns.

All very clear.  Of course (2)(b) is undeciable in general.

-- 
Ben.