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There are n triangles inscribed in a circle and all 3n of their vertices are dif

Source: 2016 239 J8

October 11, 2020
combinatoricscombinatorics unsolvedcombinatorial geometry

Problem Statement

There are nn triangles inscribed in a circle and all 3n3n of their vertices are different. Prove that it is possible to put a boy in one of the vertices in each triangle, and a girl in the other, so that boys and girls alternate on a circle.