(defparameter *moves*
  '((1 2)
    (2 1)
    (-1 2)
    (-2 1)
    (-1 -2)
    (-2 -1)
    (1 -2)
    (2 -1))
  "List of possible moves")

(defun position-valid-p (position)
  (and (> (first position) 0)
       (< (first position) 8)
       (> (second position) 0)
       (< (second position) 8)))

(defun move (position move)
  (mapcar #'+ position move))

 (defun positi target)
  (every #'identity (mapcar #'equal position target)))

(defun knight-moves (init-position target-position max-n
       &key; (unique nil))
  "Return path from INIT-POSITION to TARGET-POSITION in MAX-N moves.  

Path must not reach TARGET-POSITION in fewer than MAX-N moves

If UNIQUE is T, path must not revist already visited places"
  (let (path)
    (labels
 ((evaluate-next (current-position n)
    #+skip1 (format t "~a: ~a~%" n current-position)
    (push current-position path)
    (if (zerop n)
         (if (positi target-position)
     (return-from knight-moves (nreverse path))
     (pop path))
         (if (positi target-position)
     (pop path)
     (dolist (move *moves* (pop path))
       (let ((new-position (move current-position move)))
         (when (and (position-valid-p new-position)
      (if (and unique
        path)
          (not (find current-position path :test #'equal))
          t))
    (evaluate-next new-position (1- n)))))))))
      (evaluate-next init-position max-n))
    (rest path)))