;-*- Mode:  Lisp; Syntax: Common-lisp -*-

;;;; N-Queens rules, JTRE version
;;; Last edited 1/29/93, by KDF.

;;; Copyright (c) 1986 --- 1992 Kenneth D. Forbus, Northwestern University,
;;; Johan de Kleer and Xerox Corporation.
;;; All rights reserved.

;;; See the file legal.txt for a paragraph stating scope of permission
;;; and disclaimer of warranty.  The above copyright notice and that
;;; paragraph must be included in any separate copy of this file.

(in-package :cl-user)

(contradiction 'queens-capture *jtre*)

(rule ((:in (queen ?column1 ?row1) :var ?q1)
       (:in (queen ?column2 ?row2) :var ?q2
         :test (not (or (= ?column1 ?column2)
			(queens-okay? ?column1 ?row1
				      ?column2 ?row2)))))
      (rassert! queens-capture (death ?q1 ?q2)))