2013 IMO Problems/Problem 2
Problem
A confi�guration of 
points in the plane is called Colombian if it consists of 
red points and 
blue points, and no three of the points of the confi�guration are collinear. By drawing some lines, the plane is divided into several regions. An arrangement of lines is good for a Colombian
con�guration if the following two conditions are satis�fied:
�**no line passes through any point of the con�guration;
�**no region contains points of both colours.
Find the least value of 
such that for any Colombian con�guration of points, there is a good
arrangement of lines.
Solution
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