(zebra)
=> (((norwegian kools _.0 fox yellow)
(ukrainian chesterfields tea horse blue)
(englishman oldgolds milk snails red)
(japanese parliaments coffee zebra green)
(spaniard luckystrikes orangejuice dog ivory)))
(load "amk.scm")
(define (lefto x y l)
(fresh (h t ht)
(any (all (caro l h)
(cdro l t)
(caro t ht) ; ht = head of tail
(== h x)
(== ht y))
(all (cdro l t)
(lefto x y t)))))
(define (nexto x y l)
(any (lefto x y l)
(lefto y x l)))
(define (zebra)
(fresh (h)
(run* (h)
(all
(== h (list (list 'norwegian (_) (_) (_) (_))
(_)
(list (_) (_) 'milk (_) (_))
(_)
(_)))
(memo (list 'englishman (_) (_) (_) 'red) h)
(lefto (list (_) (_) (_) (_) 'green)
(list (_) (_) (_) (_) 'ivory) h)
(nexto (list 'norwegian (_) (_) (_) (_))
(list (_) (_) (_) (_) 'blue) h)
(memo (list (_) 'kools (_) (_) 'yellow) h)
(memo (list 'spaniard (_) (_) 'dog (_)) h)
(memo (list (_) (_) 'coffee (_) 'green) h)
(memo (list 'ukrainian (_) 'tea (_) (_)) h)
(memo (list (_) 'luckystrikes 'orangejuice (_) (_)) h)
(memo (list 'japanese 'parliaments (_) (_) (_)) h)
(memo (list (_) 'oldgolds (_) 'snails (_)) h)
(nexto (list (_) (_) (_) 'horse (_))
(list (_) 'kools (_) (_) (_)) h)
(nexto (list (_) (_) (_) 'fox (_))
(list (_) 'chesterfields (_) (_) (_)) h)
; (memo (list (_) (_) 'water (_) (_)) h)
(memo (list (_) (_) (_) 'zebra (_)) h)))))