Here is a solution for the "Who owns the zebra?" puzzle in Allegro Prolog:

  (<-- (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))
  (<-- (zebra ?h ?w ?z)
       ;; Each house is of the form:
       ;; (house nationality pet cigarette drink house-color)
       (= ?h ((house norwegian ? ? ? ?)
	      ?
	      (house ? ? ? milk ?) ? ?))
       (member (house englishman ? ? ? red) ?h)
       (member (house spaniard dog ? ? ?) ?h)
       (member (house ? ? ? coffee green) ?h)
       (member (house ukrainian ? ? tea ?) ?h)
       (iright (house ? ? ? ? ivory)
	       (house ? ? ? ? green) ?h)
       (member (house ? snails winston ? ?) ?h)
       (member (house ? ? kools ? yellow) ?h)
       (nextto (house ? ? chesterfield ? ?)
	       (house ? fox ? ? ?) ?h)
       (nextto (house ? ? kools ? ?)
	       (house ? horse ? ? ?) ?h)
       (member (house ? ? luckystrike oj ?) ?h)
       (member (house japanese ? parliaments ? ?) ?h)
       (nextto (house norwegian ? ? ? ?)
	       (house ? ? ? ? blue) ?h)
       (member (house ?w ? ? water ?) ?h)
       (member (house ?z zebra ? ? ?) ?h)
       )
  ;; This runs the query:
  (?- (zebra ?houses ?water-drinker ?zebra-owner))

For comparison, here is how the first few rules above would be expressed in Edinburgh syntax:

  nextto(X, Y, List) :- iright(X, Y, List).
  nextto(X, Y, List) :- iright(Y, X, List).
  iright(Left, Right, [Left, Right | _]).
  iright(Left, Right, [_ | Rest]) :- iright(Left, Right, Rest).