Determine all integers n≥3 for which there exists a con guration of n points in the plane, no three collinear, that can be labelled 1 through n in two different ways, so that the following
condition be satis fied: For every triple (i,j,k),1≤i<j<k≤n, the triangle ijk in one labelling has the same orientation as the triangle labelled ijk in the other, except for (i,j,k)=(1,2,3). combinatorial geometryorientationTrianglescombinatoricsRMM Shortlistdouble counting