Before revision: Let R and B be sets of n red and n blue points in the plane, respectively, with P = R \cup B. Let M be a perfect matching between points from R and B, using n straight line segments to match the points, that is, each point is an endpoint of exactly one line segment, and each line segment has one red and one blue endpoint.
After revision: Let R and B be sets of n red and n blue points in the plane, we are interested in matching red points with blue points by straight line segments to match the points, that is, each point is an endpoint of exactly one line segment, and each line segment has one red and one blue endpoint.