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set Τ: Every two triangles in T have either two common vertices, or none.

Source: Mexican Mathematical Olympiad 1991 OMM P6

July 29, 2018
combinatorial geometrygeometryset

Problem Statement

Given an nn-gon (n≥4n\ge 4), consider a set TT of triangles formed by vertices of the polygon having the following property: Every two triangles in T have either two common vertices, or none. Prove that TT contains at most nn triangles.
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