Minimum number of 'good' intersection points
Source: Japanese MO Finals 2000
February 10, 2011
combinatorial geometrycombinatorics proposedcombinatorics
Problem Statement
Finitely many lines are given in a plane. We call an intersection point a point that belongs to at least two of the given lines, and a good intersection point a point that belongs to exactly two lines. Assuming there at least two intersection points, find the minimum number of good intersection points.