In the game Four-in-a-Row, two players take it in turns to place
counters on the 5x5 board. The winner is the first player to have
4 adjacent counters in a line across or down (but not
diagonally).
It is Black's turn to play next. Where should she play her
fourth counter to be certain of winning on her fifth turn
whatever White plays?
This problem is taken from the UKMT Intermediate Mathematical
Challenges.