zebra-puzzle.lisp

(<- (member ?item (?item . ?rest)))

(<- (member ?item (?x . ?rest)) (member ?item ?rest))

(<- (nextto ?x ?y ?list) (iright ?x ?y ?list))

(<- (nextto ?x ?y ?list) (iright ?y ?x ?list))

(<- (iright ?left ?right (?left ?right . ?rest)))

(<- (iright ?left ?right (?x . ?rest))
    (iright ?left ?right ?rest))

(<- (= ?x ?x))


(<- (zebra ?h ?w ?z)
    (= ?h  ((house norwegian ? ? ? ?)                          ; 1, 10
	    ?
	    (house ? ? ? milk ?) ? ? ))                        ; 9 
    (member (house englishman ? ? ? red) ?h)                   ; 2
    (member (house spaniard dog ? ? ?) ?h)                     ; 3
    (member (house ? ? ? coffee green) ?h)                     ; 4
    (member (house ukrainian ? ? tea ?) ?h)                    ; 5
    (iright (house ? ? ? ? ivory)                              ; 6
	    (house ? ? ? ? green) ?h)
    (member (house ? snails winston ? ?) ?h)                   ; 7
    (member (house ? ? kools ? yellow) ?h)                     ; 8
    (nextto (house ? ? chesterfield ? ?)                       ; 11
	    (house ? fox ? ? ?) ?h)
    (nextto (house ? ? kools ? ?)                              ; 12
	    (house ? horse ? ? ?) ?h)
    (member (house ? ? luckystrike orange-juice ?) ?h)         ; 13
    (member (house japanese ? parliaments ? ?) ?h)             ; 14
    (nextto (house norwegian ? ? ? ?)                          ; 15
	    (house ? ? ? ? blue) ?h)
    ;; Now for the questions:
    (member (house ?w ? ? water ?) ?h)                         ; Q1
    (member (house ?z zebra ? ? ?) ?h))                        ; Q2

;; Query:

(?- (zebra ?houses ?water-drinker ?zebra-owner))