emacs lisp sandbox. see if all characters in a string are unque

dupes.el

(defun are-any-chars-duplicated (char-array &optional top-char)
  "Takes in a list of characters and returns true if there's a dupe char. returns false if all chars are unique"
  (message "top char: %s and array is" top-char)
  (princ char-array)
  (cond ((null char-array) false)
	((null top-char) (are-any-chars-duplicated (cdr char-array) (car char-array)))
	((equal (length char-array) 1) 
	 (progn 
		 (message "1 comparing %s %s" top-char (car char-array))
      		 (equal top-char (car char-array))		 
		)
	 )
	(t
	 (progn
	   (message "2 comparing %s %s" top-char (car char-array))
      	   (or (equal top-char (car char-array))
	      (or (are-any-chars-duplicated (cdr char-array) top-char)
	       (are-any-chars-duplicated  (cdr char-array) (car char-array)))
	       )
	   )
	 )
	)
  )
(message "result %s" (are-any-chars-duplicated '("a" "b" "z" "z")))