Question 2
Suppose we have a board with sixteen boxes arranged in four rows and four columns.
a) proves that seven tiles can be placed, never two in the same box, so that when you delete two rows and any two columns, there is always a piece left without deleting.
b) proves that if six tiles are placed, never two in the same box, you can always delete two rows and two columns so that all the tiles are deleted.
a) proves that seven tiles can be placed, never two in the same box, so that when you delete two rows and any two columns, there is always a piece left without deleting.
b) proves that if six tiles are placed, never two in the same box, you can always delete two rows and two columns so that all the tiles are deleted.