towers of hanoi | Takeuchi function | combinations of a set | letrec macro
; Towers of Hanoi
; HANOI - solve for N disks from X to Y via Z
; HANOI1 - solve for N disks
(defun hanoi (n x y z)
(cond ((zerop n) nil)
(t (append (hanoi (sub1 n) x z y)
(list (list x y))
(hanoi (sub1 n) z y x)))))
(defun hanoi1 (n)
(hanoi n 'left 'middle 'right))