The plane is divided by three infinite sets of parallel lines into equilateral triangles of equal area. Let M be the set of their vertices, and A and B be two vertices of such an equilateral triangle. One may rotate the plane through 120o around any vertex of the set M. Is it possible to move the point A to the point B by a number of such rotations(N Vasiliev, Moscow) geometrygeometric transformationrotationcombinatoricscombinatorial geometry