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Path: ...!weretis.net!feeder9.news.weretis.net!i2pn.org!i2pn2.org!.POSTED!not-for-mail From: Richard Damon <richard@damon-family.org> Newsgroups: comp.theory,sci.logic Subject: Re: Why does Olcott care about simulation, anyway? --- Mikes Review Date: Mon, 3 Jun 2024 21:59:02 -0400 Organization: i2pn2 (i2pn.org) Message-ID: <v3lsd6$2uv04$17@i2pn2.org> References: <v3j20v$3gm10$2@dont-email.me> <J_CdnTaA96jxpcD7nZ2dnZfqnPudnZ2d@brightview.co.uk> <v3jei1$3o3a7$1@dont-email.me> <0xqdnd8ktrnsc8D7nZ2dnZfqnPqdnZ2d@brightview.co.uk> <v3l002$5d3$1@dont-email.me> <lZadnYLpbtuB7cP7nZ2dnZfqn_udnZ2d@brightview.co.uk> <v3lrm2$4h2j$1@dont-email.me> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Injection-Date: Tue, 4 Jun 2024 01:59:02 -0000 (UTC) Injection-Info: i2pn2.org; logging-data="3111940"; mail-complaints-to="usenet@i2pn2.org"; posting-account="diqKR1lalukngNWEqoq9/uFtbkm5U+w3w6FQ0yesrXg"; User-Agent: Mozilla Thunderbird In-Reply-To: <v3lrm2$4h2j$1@dont-email.me> X-Spam-Checker-Version: SpamAssassin 4.0.0 Content-Language: en-US Bytes: 9410 Lines: 167 On 6/3/24 9:46 PM, olcott wrote: > On 6/3/2024 8:38 PM, Mike Terry wrote: >> On 03/06/2024 18:54, olcott wrote: >>> On 6/3/2024 11:25 AM, Mike Terry wrote: >>>> On 03/06/2024 04:50, olcott wrote: >>>>> On 6/2/2024 10:28 PM, Mike Terry wrote: >>>>>> On 03/06/2024 01:16, immibis wrote: >>>>>>> The halting problem says you can't find a Turing machine that >>>>>>> tells whether executing each other Turing machine will halt. >>>>>>> Simulation has nothing to do with the question. >>>>>> >>>>>> Background: >>>>>> >>>>>> PO claims to have refuted the common HP proof, e.g. as covered in >>>>>> the Linz book "An Introduction to Formal Languages and Automata". >>>>>> PO occasionally posts a link to a PDF containing an extract of the >>>>>> 5 or so pages of the book containing the proof, but I expect you >>>>>> have access to this or equivalent. >>>>>> >>>>>> In a nutshell, the proof goes: >>>>>> - Suppose H is a TM Halt decider that decides for any input >>>>>> <P><I> whether >>>>>> TM P run with input I on its input tape halts. >>>>>> [<P> is the string representation of the actual TM P, and >>>>>> <I> is the string representation of input tape I] >>>>>> - Construct from H a new TM H^ using the mechanical process >>>>>> described in the proof. >>>>>> If H exists, then its corresponding H^ also exists. >>>>>> - Show that the construction of H^ ensures that: >>>>>> - if H decides input <H^><H^> (representing H^ running with >>>>>> input <H^>) halts, >>>>>> then that implies that H^ running with input <H^> never halts >>>>>> - if H decides input <H^><H^> never halts, >>>>>> then that implies H^ running with input <H^> halts >>>>>> I.e. either way, H decides the specific input <H^><H^> >>>>>> incorrectly, contradicting >>>>>> the initial assumption that H is a halt decider. >>>>>> - So no halt decider exists. (Every proposed halt decider >>>>>> decides at least one input case >>>>>> incorrectly, viz input <H^><H^>.) >>>>>> >>>>>> PO basically claimed he had a fully coded TM H, which CORRECTLY >>>>>> decides its "nemesis" input <H^><H^>, contradicting the logic of >>>>>> the Linz proof [without pointing out any actual mistake in the >>>>>> Linz proof]. Given most people here understand the Linz proof >>>>>> well enough to see it is basically sound, people were sceptical! >>>>>> >>>>>> It turned out PO was lying about the fully coded TM, and in fact >>>>>> what he actually had was the idea behind a C program which would >>>>>> "prove" his idea. A couple of years(?) later he actually >>>>>> completed his C program and his x86utm.exe which would simulate >>>>>> the x86 code of his H and H^ to "prove" his claim. His equivalent >>>>>> of Linz H is his C function H or HH, and his equivalent of Linz H^ >>>>>> is his D or DD respectively. (They run under x86utm.exe and are >>>>>> not Windows/Unix executables.) >>>>>> >>>>>> H/HH use PARTIAL simulation of their input to decide >>>>>> halting/non-halting, returning >>>>>> 0 or 1 to communicate their decision. As you correctly point out, >>>>>> to the HP proof simulation is quite irrelevant, being just one >>>>>> kind of data manipulation that H may perform on its input string >>>>>> <P><I> before it decides the halting status. So the Linz HP proof >>>>>> covers such H, no problem. >>>>>> [I put PARTIAL in caps, just because there seems to be some >>>>>> confusion in recent threads as to what PO means by "simulation". >>>>>> He doesn't say it explicitly, despite suggestions to this effect, >>>>>> but he always means what might be called /partial/ simulation.] >>>>>> >>>>>> PO believes that by (partially) simulating the computation >>>>>> corresponding to the input <P><I> [i.e. calculating the successive >>>>>> x86 instruction steps of the computation P(I)] and monitoring the >>>>>> progress of virtual x86 state changes (like instruction address >>>>>> and op-code and so on) H could spot some pattern that reveals >>>>>> whether computation P(I) halts or not. At this point in the >>>>>> partial simulation, his H would stop simulating (aka "abort" the >>>>>> simulation) and return the appropriate halt status for input <P><I>. >>>>>> >>>>>> Nothing remarkable so far! Clearly a tight-loop in P /can/ be >>>>>> detected in this fashion, so /some/ <P><I> inputs /can/ be >>>>>> correctly determined like this. The PO claim however is that the >>>>>> specific input <H^><H^> is correctly decided by his H. In C terms >>>>>> those correspond to H(D,D) correctly returning the halt status of >>>>>> computation D(D). [PO would probably dispute this, because he >>>>>> doesn't properly understand halting or the HP generally, or in >>>>>> fact pretty much /any abstract concept/ ] >>>>>> >>>>> >>>>> Introduction to the Theory of Computation, by Michael Sipser >>>>> https://www.amazon.com/Introduction-Theory-Computation-Michael-Sipser/dp/113318779X/ >>>>> >>>>> On 10/13/2022 11:29:23 AM >>>>> MIT Professor Michael Sipser agreed this verbatim paragraph is correct >>>>> (He has neither reviewed nor agreed to anything else in this paper) >>>>> >>>>> <Professor Sipser agreed> >>>>> If simulating halt decider H correctly simulates its input D until H >>>>> correctly determines that its simulated D would never stop running >>>>> unless aborted then >>>>> >>>>> H can abort its simulation of D and correctly report that D >>>>> specifies a >>>>> non-halting sequence of configurations. >>>>> </Professor Sipser agreed> >>>>> >>>>> I have started working on what seem to be some computability issues >>>>> that you pointed out with my HH. I found that they are isolated to >>>>> one single element of HH. Essentially the details of how the master >>>>> UTM directly executed HH passes a portion of its tape to its slaves. >>>>> >>>>> Nothing else seems to have any computability issues by the measure >>>>> that I am using. >>>>> >>>>> Message-ID: <rLmcnQQ3-N_tvH_4nZ2dnZfqnPGdnZ2d@brightview.co.uk> >>>>> On 3/1/2024 12:41 PM, Mike Terry wrote: >>>>> > >>>>> > Obviously a simulator has access to the internal state >>>>> > (tape contents etc.) of the simulated machine. No problem there. >>>>> >>>>> Because of your above comment it seems that correcting this >>>>> tiny computability issue with HH is my best path forward. >>>>> >>>>> >>>>> >>>>> >>>>> You have given the following a blatantly false review when I >>>>> said the same thing another way: >>>> >>>> I have no idea what you're talking about. I did not write any of >>>> what follows below. >>>> >>>> Also I don't believe I said anything "blatantly false". You're >>>> incapable of judging what other people say or are thinking - you're >>>> often telling people that they'er lying to you and denying >>>> "previously verified facts" etc. but its all rubbish - you're in no >>>> position to make such judgements. >>>> >>>> >>>> Mike. >>>> >>> >>> You said that the execution trace that I proved is correct is >>> incorrect because you didn't like the way that HH was written. >>> You said this without looking at my proof as you are doing >>> here again. >> >> An execution trace that is produced by a program that is incorrect >> /proves/ nothing whatsoever. I don't need to look at your proof, as I >> was commenting on the value of your program output AS PROOF. >> > > I provided the execution trace that HH derives > *AND THE X86 SOURCE-CODE OF DD THAT PROVES THIS TRACE IS CORRECT* > *AND THE X86 SOURCE-CODE OF DD THAT PROVES THIS TRACE IS CORRECT* > *AND THE X86 SOURCE-CODE OF DD THAT PROVES THIS TRACE IS CORRECT* Then why did the trace not follow the call to H? You have DEFINED that to be incorrect. > > http://al.howardknight.net/?STYPE=msgid&MSGI=%3CS8CcnRadHexfe8X7nZ2dnZfqnPqdnZ2d%40brightview.co.uk%3E+ > Message-ID: <S8CcnRadHexfe8X7nZ2dnZfqnPqdnZ2d@brightview.co.uk> > > AND YOU SAID > "It shows that the simulation is "rubbish" and any trace > produced by it can just be ignored." >