Why does setf (top-left board) fails?

test.lisp

(in-package :cl-user)

;;; Everything now works thanks to Bike and http://stackoverflow.com/questions/11457071/defining-setf-expanders-in-common-lisp
;;; Learned something new today


(defun top-center (board)
  (car (cdr board)))

(defun (setf top-center) (value board)
  (setf (car (cdr board)) value))

(let ((board (list :1 :2 :3 :4))
      (player :empty))
  (format t "Board: ~A~%" board)
  (setf (top-center board) player)
  (format t "Board: ~A~%" board))