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Re: How to use not in gprolog?

From: ED-DBALI AbdelAli
Subject: Re: How to use not in gprolog?
Date: Tue, 30 Oct 2001 14:26:27 -0500

Carfield Yim a écrit :
> Hi, I need to find the negation of a clause, e.g.:
> e.g: if Z is a member of list T and Y is not a member of T, member(Z,T) 
> should return true and member(Y,T) should return false.
> I would like to get the negation of this clause, i.e.: not(member(Z,T))
> return false and not(member(Y,T)) return true. But it doesn't work. So I
> try member(X,T)\=true. and once(member(X,T))\=true. But both don't work.
> So I would like to ask how to get the negation of a clause?

Try the negation by failure (\+) (also called "not provable". see 6.18.2
in the manual):

\+ member(Y,T) will succed if Y is not member of T.

Hope this help.


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