(fact (insert ?a ?r (?a . ?r)))
(fact (insert ?a (?b . ?r) (?b . ?s))
      (insert ?a ?r ?s))

(fact (anagram () ()))
(fact (anagram (?a . ?r) ?b)
      (insert ?a ?s ?b)
      (anagram ?r ?s))

; (query (anagram ?s (s t a r)))

(fact (append () ?s ?s))
(fact (append (?f . ?r) ?s (?f . ?t))
      (append ?r ?s ?t))

(fact (palindrome ?s)
      (reverse ?s ?s))

(fact (reverse () ()))
(fact (reverse (?first . ?rest) ?rev)
      (reverse ?rest ?rest-rev)
      (append ?rest-rev (?first) ?rev))

(fact (accrev (?first . ?rest) ?acc ?rev)
      (accrev ?rest (?first . ?acc) ?rev))
(fact (accrev () ?acc ?acc))
(fact (accrev ?s ?rev)
      (accrev ?s () ?rev))

; NOTE: You may need to shrink the size of the list on your own interpreter
; (query (reverse (1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50) ?reversed))
; (query (accrev (1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50) ?reversed))

(fact (+ 0 ?n ?n))
(fact (+ (+ 1 ?x) ?y (+ 1 ?z))
      (+ ?x ?y ?z))
; (query (+ (+ 1 (+ 1 (+ 1 0))) (+ 1 (+ 1 0)) ?z))
; (query (+ (+ 1 (+ 1 0)) (+ 1 (+ 1 (+ 1 0))) ?z))

(fact (* 0 ?n 0))
(fact (* (+ 1 ?x) ?y ?z)
      (+ ?xy ?y ?z)
      (* ?x ?y ?xy))
; (query (* (+ 1 (+ 1 (+ 1 0))) (+ 1 (+ 1 (+ 1 (+ 1 0)))) ?z))
; (query (* (+ 1 (+ 1 (+ 1 (+ 1 0)))) (+ 1 (+ 1 (+ 1 0))) ?z))

(fact (- ?x ?y ?z)
      (+ ?y ?z ?x))
(fact (/ ?x ?y ?z)
      (* ?y ?z ?x))
; (query (- (+ 1 (+ 1 0)) (+ 1 0) ?z))
; (query (/ (+ 1 (+ 1 (+ 1 (+ 1 0)))) (+ 1 (+ 1 0)) ?z))

; (query (?op ?arg1 ?arg2 (+ 1 (+ 1 (+ 1 (+ 1 (+ 1 (+ 1 0))))))))