(defun negative (n)
  (cond
   ((> 0 n) t)
   )
  )

(negative -4)
; t
(negative 3)
; nil


(defun addAllNegative (l)
  (cond
   ( (null l) 0)
   ( (negative (car l)) (+ (car l) (addAllNegative (cdr l))))
   ( (addAllNegative (cdr l)))
   ))

(addAllNegative '(-4 -2 4 6 -7))
; -13


(defun allNegative (l)
  (cond
   ((null l) l)
   ( (negative (car l)) (cons (car l) (allNegative (cdr l))))
   ( (allNegative (cdr l)))
   ))

(allNegative '(-4 -2 4 6 -7))
; (-4 -2 -7)

(defun isEven (n)
  (cond
   (t (eq (+ (/ n 2) (/ n 2)) n))
   )
  )

(isEven 4)
; t
(isEven 5)
; nil


(defun allEven (l)
  (cond
   ( (null l) l)
   ( (isEven (car l)) (cons (car l) (allEven (cdr l))))
   ( (allEven (cdr l)))
   ))

(allEven '(5 2 3 4))
; (2 4)


(defun addAllEven (l)
  (cond
   ( (null l) 0)
   ( (isEven (car l)) (+ (car l) (allEven (cdr l))))
   ( (allEven (cdr l)))
   ))

(addAllEven '(5 2 3 4))
; 6