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Re: NPR, Godel, Semantic Web

• From: John Cowan <jcowan@r...>
• To: "C. M. Sperberg-McQueen" <cmsmcq@a...>
• Date: Tue, 08 May 2001 11:34:56 -0400

C. M. Sperberg-McQueen wrote:


> Sure.  Prolog texts don't talk about them in these
> terms (as Goedel sentences), but Prolog texts almost
> always mention, at some point, that depending on
> how you write your predicates some things which
> obviously follow from your program (viewed declaratively)
> cannot in fact be inferred by the Prolog system
> (working procedurally).

But is this a fact expressible *in Prolog*?
I suppose it is, since you can write a meta-circular
Prolog interpreter.

[Prolog example snipped]

> This will (I think -- I'm kind of rusty and haven't
> run this), when provided with a suitable set of facts
> involving 'parent', produce the expected result.
> It will for example, infer that 'abel' is human.
> 
> Change the order of the rules for 'human', however,
> to 3412, however, and the system will have trouble
> figuring out even that 'adam' is human.

I fed both versions into GNU Prolog 1.2.1 and it
handled both with no problem.


>    append([],L,L).
>    append([A|B],C,[A|D]) :- append(B,C,D).
> 
> and next the restricted one:
> 
>    append([],L,L) :- !.
>    append([A|B],C,[A|D]) :- append(B,C,D).
> 
> The second one works only when at the initial call the
> first two arguments are instantiated and the third is
> possibly not instantiated.

Again, I cannot provoke gprolog into returning the wrong
answer with the second definition, and I tried many cases.

-- 
There is / one art             || John Cowan <jcowan@r...>
no more / no less              || http://www.reutershealth.com
to do / all things             || http://www.ccil.org/~cowan
with art- / lessness           \\ -- Piet Hein

• Follow-Ups:
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    • From: Richard Tobin <richard@c...>
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