MathDB

We want to draw a number of straight lines such that for each square of a chessboard, at least one of the lines passes through an interior point of the square. What is the smallest number of lines needed for a (a)

3\times 3

; (b)

4\times 4

chessboard? Use a picture to show that this many lines are enough, and prove that no smaller number would do.
(M Vyalyi)

Problem Statement