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exists a monochromatic simple path of length n

Source: Israel Grosman Memorial Mathematical Olympiad 1997 p6

February 15, 2020
combinatoricsColoring

Problem Statement

In the plane are given n2+1n^2 + 1 points, no three of which lie on a line. Each line segment connecting a pair of these points is colored by either red or blue. A path of length kk is a sequence of kk segments where the end of each segment (except for the last one) is the beginning of the next one. A path is simple if it does not intersect itself. Prove that there exists a monochromatic simple path of length nn.