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n points in plane, convex heptagon and pentagon conditions

Source: Ukraine TST 2015 p9

May 2, 2020
Heptagonpentagonconvexpointscombinatoricscombinatorial geometry

Problem Statement

The set MM consists of nn points on the plane and satisfies the conditions: \bullet there are 77 points in the set MM, which are vertices of a convex heptagon, \bullet for arbitrary five points with MM, which are vertices of a convex pentagon, there is a point that also belongs to MM and lies inside this pentagon. Find the smallest possible value that nn can take .