Path: news.eternal-september.org!eternal-september.org!.POSTED!not-for-mail From: olcott Newsgroups: comp.theory Subject: =?UTF-8?Q?Re=3A_Analysis_of_Flibble=E2=80=99s_Latest=3A_Detecting_v?= =?UTF-8?Q?s=2E_Simulating_Infinite_Recursion_ZFC?= Date: Sat, 24 May 2025 00:13:53 -0500 Organization: A noiseless patient Spider Lines: 111 Message-ID: <100rkih$hnq4$1@dont-email.me> References: <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$1@dont-email.me> <87a573xz0s.fsf@bsb.me.uk> <875xhrtbpr.fsf@nosuchdomain.example.com> <100r2mb$b2b1$1@dont-email.me> <87msb2x39x.fsf@bsb.me.uk> <87tt5aslwo.fsf@nosuchdomain.example.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Injection-Date: Sat, 24 May 2025 07:13:53 +0200 (CEST) Injection-Info: dont-email.me; posting-host="f513fb0f9fd54277dcf2467a994ccda0"; logging-data="581444"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX19Po43RTjs3TYAP3d7lOArn" User-Agent: Mozilla Thunderbird Cancel-Lock: sha1:wbdG8rQ3TCoB5oUu++EWQYe/14g= X-Antivirus-Status: Clean X-Antivirus: Norton (VPS 250524-0, 5/23/2025), Outbound message In-Reply-To: <87tt5aslwo.fsf@nosuchdomain.example.com> Content-Language: en-US On 5/23/2025 10:55 PM, Keith Thompson wrote: > Ben Bacarisse writes: >> Mike Terry writes: >>> On 23/05/2025 19:37, Keith Thompson wrote: >>>> Ben Bacarisse writes: >>>>> Mike Terry writes: >>>> [...] >>>>> 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. >>>> Hmm. I don't read that the way you do. Did I miss something? >>>> It assumes that the input is a non-halting computation ("its input >>>> would never halt") and asserts that, in certain circumstances, >>>> his mythical halt decider correctly determines that the input >>>> is non-halting. >>>> When his mythical halt decider correctly determines that its input >>>> doesn't halt, it has made a correct non-halting determination. >>>> It's just a tautology. >>> >>> You're reading it the way most people would, and in the way I said Sipser >>> would be interpreting the oft-quoted "Sipser quote". I don't think you've >>> missed anything particularly. >> >> Maybe it makes less sense out of the context it was posted in. This was >> when he was being less obtuse. The computation in question only halts >> because it is halted by the decider on which it is built. It is a >> halting computation, but according to PO it can reported as not halting >> because of what would happen if it were not halted by the decider from >> which it is derived. > > I think you're misreading it (or, if you prefer, I have yet to be > convinced that I'm misreading it). > > | 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. > > Call the "halt decider" H, and the input I. If you perform the > computation specified by I, it never halts. olcott's statement > is that if H correctly determines that I never halts (assume for > now that that's possible), then H can correctly report that I > never halts. This is true, tautological, and uninteresting. > > There is *another* computation, I-simulated-by-H. This computation > may halt if H decides to halt it. But I-simulated-by-H is not I. > H's alleged job is to determine the halting status of I, not the > halting status of I-simulated-by-H. > void DDD() { HHH(DDD); return; } Unless HHH aborts its simulation of DDD it never stops running. > I think you're saying that H *incorrectly* reports that > I-simulated-by-H never halts. My interpretation is that H > *correctly* reports that I never halts. > > The above is based only on that isolated statement, without reference > to olcott's other claims. Moving on to the larger context: > > If a general solution to the halting problem were possible (we > know it isn't), a simulating halt decider could be one possible > way to approach it. It is, I suppose, a tempting idea. You could > imagine a simulator that runs a program one step at a time, and > after each step, reports that it just halted if it has, or performs > some analysis that attempts to determine that it will never halt. > If it's able to make that determination, the simulator can halt > and correctly report that the simulated program never halts. > > If the program runs on a machine with a finite number of states, this > is actually possible; a repeated state implies that the program is > in an infinite loop. The problem is that a Turing machine is not > limited to a finite number of states (including the state of the > tape), and such an analysis is not possible in the general case. > I think olcott thinks it is possible. > >> Subsequent wordings have all been about hiding this. Just prior to this >> wording was the even more explicit claim that non-halting is correct >> because of what "would happen if line 15 were commented out". It's >> always been about what would be the correct decision were the >> computation not what it actually is. > > Sure, I have no doubt that olcott has written contradictory things > (to the extent that they're clear enough to be contradictory). > I just don't think he's done is on the case of this specific > statement. > >>> I suppose Ben quoted PO saying this, because PO /uses/ it to justify that a >>> particular /halting/ computation will never halt, >> >> He may be doing that now, but he used to use this form of words to >> justify why non-halting is the correct result for some halting >> computations. Obviously, to keep people talking he has had to scramble >> to get away from what he has said in the past without repudiating it. >> No crank likes admit they were ever wrong. > > Agreed. > -- Copyright 2025 Olcott "Talent hits a target no one else can hit; Genius hits a target no one else can see." Arthur Schopenhauer