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computers / comp.theory / Re: On recursion and infinite recursion (reprise #3)

Re: On recursion and infinite recursion (reprise #3)

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From: flib...@reddwarf.jmc (Mr Flibble)
Newsgroups: comp.theory
Subject: Re: On recursion and infinite recursion (reprise #3)
Message-ID: <20220508211421.000031a0@reddwarf.jmc>
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NNTP-Posting-Date: Sun, 08 May 2022 20:14:20 UTC
Date: Sun, 8 May 2022 21:14:21 +0100
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 by: Mr Flibble - Sun, 8 May 2022 20:14 UTC

On Sun, 8 May 2022 15:39:32 -0400
Richard Damon <Richard@Damon-Family.org> wrote:

> On 5/8/22 3:06 PM, Mr Flibble wrote:
> > On Sun, 8 May 2022 14:10:13 -0400
> > Richard Damon <Richard@Damon-Family.org> wrote:
> >
> >> On 5/8/22 8:39 AM, Mr Flibble wrote:
> >>> On Sun, 8 May 2022 08:31:10 -0400
> >>> Richard Damon <Richard@Damon-Family.org> wrote:
> >>>
> >>>> On 5/8/22 8:02 AM, Mr Flibble wrote:
> >>>>> On Sun, 8 May 2022 07:45:52 -0400
> >>>>> Richard Damon <Richard@Damon-Family.org> wrote:
> >>>>>
> >>>>>> On 5/8/22 4:49 AM, Mr Flibble wrote:
> >>>>>>> On Sun, 8 May 2022 11:31:08 +0300
> >>>>>>> Mikko <mikko.levanto@iki.fi> wrote:
> >>>>>>>
> >>>>>>>> On 2022-05-07 15:19:01 +0000, Mr Flibble said:
> >>>>>>>>
> >>>>>>>>> On Sat, 7 May 2022 18:13:08 +0300
> >>>>>>>>> Mikko <mikko.levanto@iki.fi> wrote:
> >>>>>>>>>
> >>>>>>>>>> On 2022-05-07 14:20:17 +0000, Mr Flibble said:
> >>>>>>>>>>
> >>>>>>>>>>> On Sat, 7 May 2022 17:16:31 +0300
> >>>>>>>>>>> Mikko <mikko.levanto@iki.fi> wrote:
> >>>>>>>>>>>
> >>>>>>>>>>>> On 2022-05-07 14:06:12 +0000, Mr Flibble said:
> >>>>>>>>>>>>
> >>>>>>>>>>>>> On Sat, 7 May 2022 16:59:55 +0300
> >>>>>>>>>>>>> Mikko <mikko.levanto@iki.fi> wrote:
> >>>>>>>>>>>>>
> >>>>>>>>>>>>>> On 2022-05-07 12:42:50 +0000, Mr Flibble said:
> >>>>>>>>>>>>>>
> >>>>>>>>>>>>>>> On Sat, 7 May 2022 12:52:58 +0300
> >>>>>>>>>>>>>>> Mikko <mikko.levanto@iki.fi> wrote:
> >>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>> On 2022-05-06 14:02:53 +0000, Mr Flibble said:
> >>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>>> The decider could never be compiled and run in the
> >>>>>>>>>>>>>>>>> first place due to the category error in the
> >>>>>>>>>>>>>>>>> definition of the proof.
> >>>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>>> An error in the definition of the proof does not
> >>>>>>>>>>>>>>>> prevent compilation and execution of the program.
> >>>>>>>>>>>>>>>
> >>>>>>>>>>>>>>> In this case the error in the definition of the proof
> >>>>>>>>>>>>>>
> >>>>>>>>>>>>>> No part of the proof is identified as errorneous, so
> >>>>>>>>>>>>>> the rest is irrelevant. Anyway,
> >>>>>>>>>>>>>>
> >>>>>>>>>>>>>>> does prevent compilation unless
> >>>>>>>>>>>>>>
> >>>>>>>>>>>>>> There is no option here, so the "unless" is void.
> >>>>>>>>>>>>>>
> >>>>>>>>>>>>>>> the decider is made part of the program that is being
> >>>>>>>>>>>>>>> decided
> >>>>>>>>>>>>>>
> >>>>>>>>>>>>>> The decider is made a part of the program discussed in
> >>>>>>>>>>>>>> the proof.
> >>>>>>>>>>>>>>> in which case we get a function call-like infinite
> >>>>>>>>>>>>>>> recursion instead
> >>>>>>>>>>>>>>
> >>>>>>>>>>>>>> We get or we don't get, depending on how the halt
> >>>>>>>>>>>>>> decider candidate attempts to decide.
> >>>>>>>>>>>>>>
> >>>>>>>>>>>>>>> (as described by Pete Olcott) and we are attempting
> >>>>>>>>>>>>>>> (and failing) to decide if a procedure halts rather
> >>>>>>>>>>>>>>> than if a program halts.
> >>>>>>>>>>>>>>
> >>>>>>>>>>>>>> In any case, the decider candidate fails to give the
> >>>>>>>>>>>>>> correct answer, and therefore is not a halt decider.
> >>>>>>>>>>>>>> Note that this is correctly inferred in the proof.
> >>>>>>>>>>>>>> Therefore either the conclusion of the proof is
> >>>>>>>>>>>>>> correct or you are wrong.
> >>>>>>>>>>>>>
> >>>>>>>>>>>>> No answer is ever given due to the infinite recursion.
> >>>>>>>>>>>>
> >>>>>>>>>>>> True about some candidates, false about others. For
> >>>>>>>>>>>> example, a candidate that always says "no" is not
> >>>>>>>>>>>> infinitely recursive but is wrong in the particular case
> >>>>>>>>>>>> discussed in the proof. But anyway, you have confirmed
> >>>>>>>>>>>> the conclusion of the proof.
> >>>>>>>>>>>
> >>>>>>>>>>> False. The proof is not cognisant of the presence of the
> >>>>>>>>>>> infinite recursion. The decider can never return an
> >>>>>>>>>>> answer of halts/doesn't halt due to the infinite
> >>>>>>>>>>> recursion.
> >>>>>>>>>>
> >>>>>>>>>> The correct term is decider candidate. It is not a decider
> >>>>>>>>>> because the infinite recursion prevents it from halting in
> >>>>>>>>>> finite time.
> >>>>>>>>>>
> >>>>>>>>>> You cannot call the proof incorrect merely because it
> >>>>>>>>>> agrees with you.
> >>>>>>>>>
> >>>>>>>>> Try actually reading what Strachey wrote: a contradiction
> >>>>>>>>> arises based on the result of evaluating T[P] however T[P]
> >>>>>>>>> is never evaluated due to the infinite recursion: a fact
> >>>>>>>>> ignored by the proof.
> >>>>>>>>
> >>>>>>>> If you can prove that the program does give the correct
> >>>>>>>> result in that case you have proven Strachey wrong.
> >>>>>>>> Otherwise you haven't.
> >>>>>>>
> >>>>>>> Strachey is wrong because he neglected to account for the
> >>>>>>> infinite recursion; this should be obvious to anyone who has
> >>>>>>> actually read and understood what Strachey wrote: it seems
> >>>>>>> that you haven't.
> >>>>>>>
> >>>>>>> /Flibble
> >>>>>>>
> >>>>>>
> >>>>>> No, because if T gets stuck in an infinite recursion, it is
> >>>>>> wrong, because it failed to answer in finite time.
> >>>>>>
> >>>>>> If T does answer in finite time, then there never was an
> >>>>>> infinite recursion.
> >>>>>>
> >>>>>> All you have shown is that there exists a WRONG method to build
> >>>>>> a T that gets stuck, Like a T that needs to run its input to
> >>>>>> completion to answer about it.
> >>>>>
> >>>>> I have shown that [Strachey, 1965] contains an infinite
> >>>>> recursion and is thus invalid.
> >>>>>
> >>>>> /Flibble
> >>>>>
> >>>>
> >>>> No, you haven't. All you have shown is that one way to attempt to
> >>>> make the program that Strachev says doesn't exist, fails due to
> >>>> getting caught in infinite recursion.
> >>>>
> >>>> That just helps confirm Strachev, not refute it.
> >>>
> >>> Nope. Strachey's proof is based on a contradiction relating to
> >>> evaluating the result of T[P] however T[P] can never be evaluated
> >>> if there is an infinite recursion.
> >>>
> >>> /Flibble
> >>>
> >>
> >> Nope, because if T actually meets the requirement to be able to
> >> take ANY program and answer, then it need to be able to take a
> >> program that uses a copy of T in it, as that is a valid program.
> >>
> >> If T gets into an infinite recursion on such a program, it is that
> >> *T* fails to meet the requirements, not that the such a program is
> >> invalid to give to T.
> >>
> >> This means that the program T is Strachey's proof can't just
> >> execute its input to get the needed answer, as that makes it (T)
> >> not meet its requirements.
> >>
> >> Thus, the "recursion" error isn't in the proof of impossibility,
> >> but in the candidate T that is attempting to be the counter
> >> example for the proof.
> >>
> >> Recursion is allowed in programming and in math. If you try to just
> >> ban it, you will find you logic can't handle what it needs to.
> >
> > You are simply wrong, and fractally so. Try reading what Strachey
> > actually wrote.
> >
> > /Flibble
> >
>
> I have.
>
> T[R] is defined to be a boolean function that returns True if routine
> R (taking no parameters) Halts, and False if R never halts.
>
> Thus, for ANY input program, T must itself Halt, that requirement
> INCLUDES if R calls T[R], so if T gerts into infinite recursion and
> thus not answer, T has failed its specification.
>
> If you want to define that T can't take the R he defines, then why is
> that NOT a program? What "rule of programs" has it violated, note R
> getting stuck in an infinite loop is one of the purposes that T is
> supposed to handle.
>
> T has no requirement that the input R halts or in fact, any
> requirement other than it be a program. Thus the fact that R gets
> "hung up" in an infinite recursion isn't an error in building R, but
> it IS a error in the design of T, as T is REQUIRED, to meet its
> definition to always answer.
>
> Thus, your claim about T not answering because it got stuck in an
> infinite recursion is just a statement that a T built that way jus
> fails to meet its requriement.
>
> Note, there is NO requirement in the problem that T[R] actually runs
> R, and in fact, you are proving that it CAN'T (at least not without
> some way to stop it) as that leads to T inherently failing for this
> sort of program.
>
> Note, any "rule" you try to invent that prohibits this "impossible
> program" must also take into account the "compliant" program C that
> should be allowed that just calls T[C] and doesn't what it says, and
> the two fixed behavior ones that call T with themselfs and then
> unconditionally Halt or Loop. All three of these should be "legal" as
> they do have definite answers that work, so arguements on
> contrariness don't apply.

You continue to be wrong and fractally so. The infinite recursion will
ALWAYS happen according to the definition of the proof. Again: read AND
UNDERSTAND what Strachey actually wrote.

/Flibble

SubjectRepliesAuthor
o On recursion and infinite recursion (reprise #3)

By: Mr Flibble on Thu, 5 May 2022

66Mr Flibble
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