(defun fact(n) ; Problema 1
    (cond ((zerop n) 1)
          ((equal n 1) 1)
          (t (* n (fact (- n 1))))
    )
)

(defun fibonacci(n) ; Problema 2
    (cond ((zerop n) 0)
          ((equal n 1) 1)
          (t (+ (fibonacci(- n 1)) (fibonacci(- n 2))))
    )
)

(defun my_member(x lst) ; Problema 3
    (cond ((null lst) nil)
          ((equal (car lst) x) t)
          (t (my_member x (cdr lst)))
    )
)

(defun trim-head (lst n) ; Problema 4
    (cond ((> n (length lst)) '(nil))
          ((null lst) '(nil))
          ((zerop n) lst)
          (t (trim-head (cdr lst) (- n 1)))
    )
)

(defun trim-tail (lst n) ; Problema 5
    (reverse (trim-head (reverse lst) n))
)

(defun count-atoms (lst) ; Problema 6
    (cond ((null lst) 0)
          (t (+ (cond ((atom (car lst)) 1)
                      ((count-atoms (car lst))))
               (count-atoms (cdr lst))))
    )
)

(defun squash (lst) ; Problema 10
    (cond ((null lst) nil)
          ((atom lst) (list lst))
          (t (append (squash (car lst)) (squash (cdr lst))))
    )
)

(defun presentp (n lst) ; Problema 9
    (cond ((null lst) nil)
          ((cond ((atom (car lst)) (equal (car lst) n))
                 ((presentp n (car lst)))))
          (t (presentp n (cdr lst)))
    )
)

(defun rev (lst a) ; Problema 8
    (cond ((null lst) a)
          (t (rev (cdr lst) (cons (car lst) a)))
    )
)

(defun my_reverse(lst) (rev lst nil))

(defun inc (n) (+ n 1)) ; Problema 7
(defun my_add(n1 n2 ac)
    (cond ((equal ac (+ n1 n2)) ac)
          (t (my_add n1 n2 (inc ac)))
    )
)