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min no of convex sets whose union is M (plane - 3 vertices of triangle)

Source: Czech and Slovak Olympiad 1980, National Round, Problem 3

September 13, 2024
combinatoricscombinatorial geometrygeometryConvex Set

Problem Statement

The set MM was formed from the plane by removing three points A,B,CA, B, C, which are vertices of the triangle. What is the smallest number of convex sets whose union is MM?
[hide=original wording] Množina M Vznikla z roviny vyjmutím tří bodů A, B, C, které jsou vrcholy trojúhelníka. Jaký je nejmenší počet konvexních množin, jejichž sjednocením je M?