(defun duplicatep (list)
  (labels ((find-elt (list elt)
             (cond ((null list) nil)
                   ((= (car list) elt) t)
                   (t (find-elt (cdr list) elt)))))
    (cond ((null list) nil)
          ((find (car list) (cdr list)) t)
          (t (duplicatep (cdr list))))))



LIST-NAMED-CLASS> (duplicatep '(1 2 3 4 5 6 7 8 9 10))
NIL
LIST-NAMED-CLASS> (duplicatep '(1 2 3 4 5 6 7 8 9 10 1))
T
LIST-NAMED-CLASS> (duplicatep '(1 2 3 4 5 6 7 8 9 10 8))
T