def make_move(self, move):
        """Apply move to current game.

           Arguments:
           move:  A pair (r, c) representing square self._state[0][r][c]

           Assumptions:
           (r, c) are valid coordinates for self._state[0].  If they represent
           a valid move for current player, then the current player occupies
           that position and the opponent becomes the current player.
           Otherwise self._state is left unchanged.

           Returns:
           New TicTacToe gamestate with move recorded on
           self._state[0] and current player replaced by opponent, if
           this is legal.  Otherwise return None.
        """

        #If given spot is not valid move, return None
        if move not in self.next_move():

            return None

        #Otherwise, put current player in that spot and return new gamestate
        else:

            state = list(copy.deepcopy(self._state[0]))
            state[move[0]][move[1]] = self.player()
            return TicTacToe((tuple(state), self.opponent()))