Question 9
We have a $7 \times 7$ board. Julián colours 29 cells black. Then Pilar must place on the board an L-shaped piece (an "elbow") that covers exactly three cells, like those in the figure (oriented in any way). If the three cells covered by the elbow are black, Pilar wins.
Determine whether Julián can make the colouring in such a way that it is impossible for Pilar to win.
Determine whether Julián can make the colouring in such a way that it is impossible for Pilar to win.