Let n be an odd natural number. We consider an n×n grid which is made up of n2 unit squares and 2n(n+1) edges. We colour each of these edges either <spanclass=′latex−italic′>red</span> or <spanclass=′latex−italic′>blue</span>. If there are at most n2<spanclass=′latex−italic′>red</span> edges, then show that there exists a unit square at least three of whose edges are <spanclass=′latex−italic′>blue</span>.