;; Sample Solution to Question 4

(defun three-in-a-row-p ( board )
  (cond
    ((check-win board 'x) 1)
    ((check-win board 'o) -1)
    (t 0)
  )
)

(defun check-win ( board player )
  (or
    (check-row board player 0)
    (check-row board player 3)
    (check-row board player 6)
  )
)

(defun check-row ( board player where )
  (and
    (equal player (nth where board))
    (equal player (nth (+ where 1) board))
    (equal player (nth (+ where 2) board))
  )
)