Path: news.eternal-september.org!eternal-september.org!.POSTED!not-for-mail From: Mikko Newsgroups: comp.theory Subject: Re: How to write a self-referencial TM? Date: Fri, 16 May 2025 10:27:05 +0300 Organization: - Lines: 58 Message-ID: <1006pc9$3ld84$1@dont-email.me> References: <1e4f1a15826e67e7faf7a3c2104d09e9dadc6f06.camel@gmail.com> <1002akp$2i4bk$2@dont-email.me> <479eebef3bd93e82c8fe363908b254b11d15a799.camel@gmail.com> <1002jkk$2k00a$3@dont-email.me> <05e306f20fcb7c88c497e353aaecd36b30fc752a.camel@gmail.com> <10053hb$3759k$1@dont-email.me> <10055rn$37m1t$1@dont-email.me> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Injection-Date: Fri, 16 May 2025 09:27:06 +0200 (CEST) Injection-Info: dont-email.me; posting-host="1dfa167546830b8917680f44790d20f0"; logging-data="3847428"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1/1qIOaAvq0GZfKtipCqts5" User-Agent: Unison/2.2 Cancel-Lock: sha1:JndK/vJQD59WMgHRMARbWh0lPqo= On 2025-05-15 16:47:49 +0000, olcott said: > On 5/15/2025 11:08 AM, Mike Terry wrote: >> On 14/05/2025 18:53, wij wrote: >>> On Wed, 2025-05-14 at 12:24 -0500, olcott wrote: >>>> On 5/14/2025 11:43 AM, wij wrote: >>>>> On Wed, 2025-05-14 at 09:51 -0500, olcott wrote: >>>>>> On 5/14/2025 12:13 AM, wij wrote: >>>>>>> Q: Write a turing machine that performs D function (which calls itself): >>>>>>> >>>>>>> void D() { >>>>>>>     D(); >>>>>>> } >>>>>>> >>>>>>> Easy? >>>>>>> >>>>>>> >>>>>> >>>>>> That is not a TM. >>>>> >>>>> It is a C program that exists. Therefore, there must be a equivalent TM. >>>>> >>>>>> To make a TM that references itself the closest >>>>>> thing is a UTM that simulates its own TM source-code. >>>>> >>>>> How does a UTM simulate its own TM source-code? >>>>> >>>> >>>> You run a UTM that has its own source-code on its tape. >>> >>> What is exactly the source-code on its tape? >>> >> >> Every UTM has some scheme which can be applied to a (TM & input tape) >> that is to be simulated.  The scheme says how to turn the (TM + input >> tape) into a string of symbols that represent that computation. >> >> So to answer your question, the "source-code on its tape" is the result >> of applying the UTM's particular scheme to the combination (UTM, input >> tape) that is to be simulated. >> >> If you're looking for the exact string symbols, obviously you would >> need to specify the exact UTM being used, because every UTM will have a >> different answer to your question. >> >> >> Mike. > > These things cannot be investigated in great > depth because there is no fully encoded UTM in > any standard language. Investigations do not need a standard language. For an investigation an ad hoc language is good enough and usually better. -- Mikko