8.7

Part of 2001 All-Russian Olympiad Regional Round

Problems(1)

4 colors in 5x5 board - All-Russian MO 2001 Regional (R4) 8.7

Source:

Is it possible to paint the cells of a

5\times 5

4

colors so that the cells standing at the intersection of any two rows and any two columns were painted in at least

3

combinatoricsColoring