Question 51
Mari and Jüri play the following game on an infinite grid: They take turns with Mari starting, Mari colours one uncolored square red in each of her turns, Jüri colours one uncolored square blue in each of his turns. If the centers of any four squares of the same colour form the corners of some square, then this player wins. Does either player have a winning strategy? If so, what is the least number of turns to guarantee a victory?