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From: reddy@uiucdcs.CS.UIUC.EDU
Newsgroups: net.lang.prolog
Subject: Re: Standard behavior?
Message-ID: <29700030@uiucdcs>
Date: Sat, 7-Jun-86 20:19:00 EDT
Article-I.D.: uiucdcs.29700030
Posted: Sat Jun  7 20:19:00 1986
Date-Received: Mon, 9-Jun-86 03:06:28 EDT
References: <6500005@uicsl>
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Nf-From: uiucdcs.CS.UIUC.EDU!reddy    Jun  7 19:19:00 1986


/* Written  6:10 pm  Jun  1, 1986 by blenko@burdvax.UUCP in uiucdcs:net.lang.prolog */
So the discussion reduces to establishing the logical or non-logical
character of call() and negation-by-failure(). I will speculate that
the meaning of call() can be captured by a suitable application of
first-order logic, due to its definition in terms of constructive
proofs (I have something along the lines of Perlis' AIJ (1985) article
in mind here). I am side-stepping the problem of incompleteness of
logic-programming interpreters w.r.t resolution.

	Tom
/* End of text from uiucdcs:net.lang.prolog */

We should be careful about what we mean by negation-by-failure.  If it is
applied to ground atoms, it is certainly logical (see for example Lloyd's
book).  But when it is applied to non-ground atoms, it messes up with the
quantification of variables in the atoms.  Hence, it should not be
surprising that it is possible to define cut etc using it.