I'm not sure if this works, so here's a test blather.... I rather like Isoptikon, a free Geometry program. It can be gotten for windows or Mac at http://itia.math.uch.gr/%7Epamfilos/#iso . Dan Hoey has shown the Reid hexagon is unique. A Reid polygon is a set of Golumb rulers with 0, 1, 2, ..., n-1 marks that measure every distance from 1 to BinomialCoefficent(n+2,3). 1,4,25,6,14,3 - 8,10,16,12,9 - 2,22,19,13 - 7,33,11 - 15,27 - 39 New Scientist magazine: By firing Beryllium-14 atoms at a carbon target, investigators seemingly got Beryllium-10 and tetraneutrons. --Ed Pegg Jr