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BIRDS.PL
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1991-10-31
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960b
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42 lines
/* From the book PROLOG PROGRAMMING IN DEPTH
by Michael A. Covington, Donald Nute, and Andre Vellino.
Copyright 1988 Scott, Foresman & Co.
Non-commercial distribution of this file is permitted. */
/* Modified for Quintus Prolog by Andreas Siebert */
/* BIRDS.PL */
/* For use with DREASON.PL */
/*
* N.B.: This file will not reconsult properly in Arity Prolog
* and in some other Prologs because the interpreter will
* take the two defeasible rules to be facts for the
* predicate := instead of rules for the predicate flies.
* Since these rules are not contiguous in the file, the
* first rule will be retracted when the second rule is
* added to the database.
*/
:- no_style_check(discontiguous).
:- dynamic (neg)/1, bird/1, penguin/1.
:- multifile (neg)/1.
flies(X) :=
bird(X).
neg flies(X) :-
penguin(X).
neg flies(X) :^
sick(X).
flies(buzz) :=
true.
bird(woody).
bird(X) :-
penguin(X).
penguin(chilly).