(defun factorial (x)
  (cond ((= x 1) 1)
	(t (* x (factorial (- x 1))))))

(factorial 5)

(defun fib (x)
  (cond ((zerop x) 0)
	((= x 1) 1)
	(t (+ (fib (- x 1)) (fib (- x 2))))))

(fib 9)

(defun my-member (U lst)
  (cond ((null lst) nil)
	((equal U (car lst)) lst)
	(t (my-member U (cdr lst)))))

(my-member 'flower '(tree flower power))

(defun trim-head (l n)
  (cond ((zerop n) l)
	(t (trim-head (cdr l) (- n 1)))))

(trim-head '(a b c d) 1)

(defun trim-tail (l n)
  (cond ((zerop n) l)
	(t (trim-tail (reverse (cdr (reverse l))) (- n 1)))))

(trim-tail '(a b c d) 2)

(listp (car '( (a b c) d e f)))

(defun count-atoms (l)
  (cond ((null l) 0)
	 ((atom (car l)) (+ 1 (count-atoms(cdr l))))
	 ((listp (car l)) (+ (count-atoms(car l)) (count-atoms(cdr l))))))

(count-atoms '(a b c (a b c d) ()))

(defun inc (x)
  (+ x 1))

(defun dec (x)
  (- x 1))

(defun plus (a b)
  (cond ((zerop b) a)
	(t (plus (inc a) (- b 1)))))

(plus 322 10)


(defun my-reverse (l)
  (cond ((null l) nil)
	( t (append (my-reverse (cdr l)) (list (car l))))))

(my-reverse '(a b c d e f g h ( y o k o) h a))
(reverse '(a b c d e f g h ( y o k o) h a))

(defun my-presentp (U l)
  (cond ((null l) nil)
	((equal (car l) U) t)
	((listp (car l)) (or (my-presentp U (car l)) (my-presentp U (cdr l))))
	(t (my-presentp U (cdr l) ))))

(my-presentp 'flowers '(yea ( croc (flowerss beauty flowers) jumbo mumbo ) flowerss))

(defun squash (l)
  (cond ((null l) nil)
	((atom (car l)) (append (list (car l)) (squash (cdr l))))
	((listp (car l)) (append (squash (car l)) (squash (cdr l))))))

(squash '(yea ( croc (flowerss beauty ( ( ()))) () jumbo mumbo )))
(car (cdr  '(yea '( croc) '((flowerss beauty '())) '() jumbo mumbo )))
(car (cdr '(yea (crocodile))))