; -*- Mode: Lisp; -*- ;;;; N-Queens rules, FTRE version ;;;; Modified: forbus on Tue Apr 2 10:24:59 1996 ;;; Copyright (c) 1992-1996 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 :COMMON-LISP-USER) (rule ((queen ?column1 ?row1) (queen ?column2 ?row2) :TEST (not (or (= ?column1 ?column2) (queens-okay? ?column1 ?row1 ?column2 ?row2)))) (rassert! Contradiction))