;;11/9/21

(defun sumlist (l)
  (cond
    ( (null l) 0)
    ( t (+ (car l) (sumlist (cdr l))))
  )
)

(defun multlist (l)
  (cond
    ( (null l) 1)
    ( t (* (car l) (multlist (cdr l))))
  )
)

(sumlist '(2 4 6))

(multlist '(2 4 6))

(defun rember (x l)
 ( cond
   ( (null l) l)
   ( (eq x (car l)) (rember x (cdr l)))
   ( t (cons (car l) (rember x (cdr l))))
 )
)

(rember 2 '(2 3 7))
(rember 2 '(3 2 4 5))
(rember 2 '(3 2 4 2 5))

(defun firsts (l)
  ( cond
    ( (null l) l)
    ( t (cons (car (car l)) (firsts (cdr l))))
  )
)

(firsts '((4 5) (6 3) (8 3 1)))

(defun replace (new old l)
  ( cond
    ( (null l) l)
    ( (eq old (car l)) (cons new (cdr l)))
    ( t (cons (car l) (replace new old (cdr l))))
  )
)

(defun replaceall (new old l)
  ( cond
    ( (null l) l)
    ( (eq old (car l)) (cons new (replaceall new old (cdr l))))
    ( t (cons (car l) (replaceall new old (cdr l))))
  )
)

(replace 3 6 '(9 4 6 5))
(replace 3 6 '(6 5 7 6))

(replaceall 3 6 '(6 5 7 6))

(defun replace (new old l)
  ( cond
    ( (null l) l)
    ( (eq old (car l)) (cons new (cdr l)))
    ( t (cons (car l) (replace new old (cdr l))))
  )
)

(defun insertallR (new old l)
  ( cond
    ( (null l) l)
    ( (eq old (car l)) (cons (car l) (cons new (insertallR new old (cdr l)))))
    ( t (cons (car l) (insertallR new old (cdr l))))
  )
)

(insertR 3 6 '(6 5 2))
(insertR 3 6 '(6 7 8))
(insertR 3 6 '(1 4 6 7 6))
(insertallR 3 6 '(1 4 6 7 6))