Path: ...!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!eternal-september.org!.POSTED!not-for-mail From: Keith Thompson Newsgroups: comp.theory Subject: Re: Incorrect requirements --- Computing the mapping from the input to HHH(DD) Date: Fri, 09 May 2025 20:12:39 -0700 Organization: None to speak of Lines: 83 Message-ID: <87msblcg60.fsf@nosuchdomain.example.com> References: <87msbmeo3b.fsf@nosuchdomain.example.com> <87ecwyekg2.fsf@nosuchdomain.example.com> <87bjs2cyj6.fsf@nosuchdomain.example.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Injection-Date: Sat, 10 May 2025 05:12:40 +0200 (CEST) Injection-Info: dont-email.me; posting-host="8bc3288f4b42a8d6fbbe53fa021cb69a"; logging-data="3468361"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX18hJATbRjamgOVDcpfXfUqU" User-Agent: Gnus/5.13 (Gnus v5.13) Cancel-Lock: sha1:JuJmJYfzw0Wx60RU5j6ccUTRTEc= sha1:tKBhLcoh6emw0NBAiU2/wdeJtug= Bytes: 5346 Mike Terry writes: > On 09/05/2025 03:23, Keith Thompson wrote: >> Richard Damon writes: >>> On 5/8/25 7:53 PM, olcott wrote: >> [...] >>>> void DDD() >>>> { >>>>   HHH(DDD); >>>>   return; >>>> } >>>> We don't need to look at any of my code for me >>>> to totally prove my point. For example when >>>> the above DDD is correctly simulated by HHH >>>> this simulated DDD cannot possibly reach its own >>>> "return" instruction. >>> >>> And thus not correctly simulatd. >>> >>> Sorry, there is no "OS Exemption" to correct simulaiton;. >> Perhaps I've missed something. I don't see anything in the above >> that >> implies that HHH does not correctly simulate DDD. Richard, you've read >> far more of olcott's posts than I have, so perhaps you can clarify. >> If we assume that HHH correctly simulates DDD, then the above code >> is >> equivalent to: >> void DDD() >> { >> DDD(); >> return; >> } >> which is a trivial case of infinite recursion. As far as I can >> tell, >> assuming that DDD() is actually called at some point, neither the >> outer execution of DDD nor the nested (simulated) execution of DDD >> can reach the return statement. Infinite recursion might either >> cause a stack overflow and a probable program crash, or an unending >> loop if the compiler implements tail call optimization. >> I see no contradiction, just an uninteresting case of infinite >> recursion, something that's well understood by anyone with a >> reasonable level of programming experience. (And it has nothing to >> do with the halting problem as far as I can tell, though of course >> olcott has discussed the halting problem elsewhere.) >> Richard, what am I missing? > > Depends on what you've picked up on. > > Do you get that HHH's simulation is a /partial/ simulation? HHH is > free to simulate a few x86 instructions of DDD, and then simply > abandon the simulation and return. Since such a simulation is > obviously NOT equivalent to a direct call to DDD, and above you argue > that it is, I'd say you've missed that. I have not read the vast majority of olcott's post here. For most of the recent discussion I had with him, there was no mention of partial simulation. olcott finally said something about simulating just a few instructions, but at the same time he finally indicated that understanding his arguments would require an understanding of x86 machine and/or assembly language. That's when I bailed out. A "correct simulation", as I understand the term, would require fully simulate the execution of DDD. If DDD never halts, its simulation never halts. olcott seems to think that he's found a way around this that's relevant to the Halting Problem, but I withdrew before getting to that point. [...] > Other posters have suggested that what you're missing is some > variation of "once you answer PO's current question (about whether the > simulation by HHH progresses as far as DDD's return) PO will go on to > do something else wrong". Well, of course he will, but that's hardly > something you're missing if he's not done it yet! :) I'd also say > it's no reason not to answer PO's question honestly, acknowledging > that he is talking about /partial/ simulations... The time to > challenge future mistakes he will go on to make, is when he makes > them. That sounds about right. -- Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com void Void(void) { Void(); } /* The recursive call of the void */