In this case, when player O has just played to send player X at the center but this sub-board has already been won:
Player X can choose which sub-board to play on. Every sub-board can is fair game except the center one which has already been won. In this case every sub-board except the center one should be highlighted.
In this case, when player O has just played to send player X at the center but this sub-board has already been won:
Player X can choose which sub-board to play on. Every sub-board can is fair game except the center one which has already been won. In this case every sub-board except the center one should be highlighted.