私のはこう。

>>65
(defun pos+ (lst)
(let ((n -1))
(mapcar #'(lambda (x)
(setf n (+ n 1))
(+ n x))
lst))))

>>67
(defun occurrences-help (count lst)
(let* ((elem (car lst))
(a (assq elem count)))
(cond
((null lst) (sort count #'(lambda (a b) (> (cdr a) (cdr b)))))
(a (setf (cdr a) (+ (cdr a) 1))
(occurrences-help count (cdr lst)))
(t (occurrences-help (cons (cons elem 1) count) (cdr lst))))))

(defun occurrences (lst)
(occurrances-help '() lst))