(define insert
  L      0 E -> [E|L]
  [L|Ls] N E -> [L|(insert Ls (- N 1) E)])

(define seq
  Start Start -> [Start]
  Start End   -> [Start|(seq (+ Start 1) End)])

(define append-lists
  []    -> []
  [A|B] -> (append A (append-lists B)))

(define permutate
  []    -> [[]]
  [H|T] -> (append-lists (map (/. P
                                  (map (/. N
                                           (insert P N H))
                                       (seq 0 (length P))))
                              (permute T))))