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- Newsgroups: sci.math
- Path: sparky!uunet!snorkelwacker.mit.edu!galois!riesz!jbaez
- From: jbaez@riesz.mit.edu (John C. Baez)
- Subject: Re: Trivial! (was: Re: Help X^2 == Y mod N)
- Message-ID: <1992Nov5.210504.3520@galois.mit.edu>
- Sender: news@galois.mit.edu
- Nntp-Posting-Host: riesz
- Organization: MIT Department of Mathematics, Cambridge, MA
- References: <1992Nov5.001930.24516@galois.mit.edu> <1992Nov5.031326.11279@CSD-NewsHost.Stanford.EDU>
- Date: Thu, 5 Nov 92 21:05:04 GMT
- Lines: 40
-
- In article <1992Nov5.031326.11279@CSD-NewsHost.Stanford.EDU> pratt@Sunburn.Stanford.EDU (Vaughan R. Pratt) writes:
- >In article <1992Nov5.001930.24516@galois.mit.edu> jbaez@riesz.mit.edu (John C. Baez) writes:
- >>Some of you may remember the post in which I described a system of logic
- >>with a predicate T such that T(P) means "P is trivial". T(P) -> P
- >>but not vice-versa. (Well, in real life T(P) does not imply P, but
- >>we're just joking around here.) T(P) -> T(T(P)), though.
- >
- >Isn't T->TT contradicted by the example of Norbert Wiener? After being
- >challenged about T(P) for some P that probably no one remembers any
- >more, Wiener wandered away in deep thought and returned 20 minutes
- >later to announce triumphantly that it was indeed trivial.
- >
- >Or did you mean Trivial(P) -> Triumphantly(Trivial(P))?
- >
- >(MIT is the official repository of Wiener stories, so I fully expect a
- >suitable counterstory from John.)
-
- I'll have to make up an apocryphal one. Upon his return, the students
- asked if it was *trivially* true that his statement was trivial. Wiener
- wandered off for another couple of hours and returned saying, yes, it
- was indeed trivial.
-
- I've gotten 2 emails so far reminding me of this joke, actually. My
- opinioni is that this joke is funny precisely because it violates the
- principle that T(P) -> T(T(P)).
-
- I was also reminded that T(P) -> T(T(P)) is one of the properties that a
- provability predicate must satisfy to derive Loeb's theorem. This says
- that (P -> T(P)) -> P.
-
- I.e., "this statement is provable," suitably mathematized by
- Goedel-number, is in fact provable.
-
- Similarly, "if this statement is true, it's trivial" is trivial.
- (Now I am joking again, just in case anyone's having trouble keeping
- things straight.) Why? Let P = "if this statement is true, it's
- trivial." If P is true, then if P is true, it's trivial. In other
- words, if P is true, it's trivial! We have just shown that P is true.
- So it follows trivially that P is trivial.
-
-