I am stuck on problem 39 in brualdi 's book Ch-1 4edition. It's: Take any set 2n of points in the plane with no three collinear and then arbitrarily color each point red or blue. Prove that it's always possible to pair up the red points with the blue points by drawing line segments connecting them so that no two of the line segments intersect. I do not want the solution . I just want to understand the problem.